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FOUS11 KWBC 090725
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
324 AM EDT MON APR 09 2018

VALID 12Z MON APR 09 2018 - 12Z THU APR 12 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE NORTHERN
ROCKIES...

A RIDGE OF HIGH PRESSURE AND DRY CONDITIONS ARE EXPECTED TO
PREVAIL ACROSS MUCH OF THE WESTERN U.S. THROUGH MON. BY EARLY
TUE...MODELS SHOW THE RIDGE BEGINNING TO GIVE WAY TO A NEGATIVELY
TILTED UPPER TROUGH LIFTING FROM THE EASTERN PACIFIC INTO WESTERN
CANADA AND PACIFIC NORTHWEST. LIGHT TO MODERATE PRECIPITATION IS
EXPECTED TO ACCOMPANY THE ASSOCIATED COLD FRONT AS IT MOVES MOVES
ACROSS THE NORTHWEST INTO THE NORTHERN ROCKIES LATE TUE INTO EARLY
WED. SNOW LEVELS ARE EXPECTED TO BE QUITE HIGH AHEAD OF THE
FRONT...WITH ACCUMULATING SNOWS CONFINED MAINLY TO THE HIGHER
PEAKS OF THE NORTHERN CASCADES ON TUE. HOWEVER...POST-FRONTAL
ONSHORE FLOW ALONG WITH FALLING SNOW LEVELS MAY SUPPORT SOME HEAVY ACCUMULATIONS ACROSS THE OLYMPICS AND NORTHERN CASCADES BY EARLY
WED. THIS SYSTEM IS EXPECTED TO QUICKLY MOVE EAST...WITH SNOW
LEVELS RISING AHEAD OF THE NEXT SYSTEM APPROACHING THE COAST ON
WED. THIS NEXT SYSTEM IS EXPECTED TO BE STRONGER THAN THE
PREVIOUS...WITH SNOW LEVELS DROPPING DRAMATICALLY AS A DEEP UPPER
TROUGH AND ITS ASSOCIATED FRONT MOVE INLAND WED NIGHT. BY THU
MORNING...THE HEAVY SNOW THREAT IS EXPECTED TO EXTEND SOUTH INTO
THE SOUTHERN CASCADES...NORTHWEST CA COASTAL RANGES AND THE
NORTHERN SIERRA.

THE PROBABILITY OF SIGNIFICANT ICING (0.25 INCH OR MORE) IS LESS
THAN 10 PERCENT.

PEREIRA

$$




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FOUS11 KWBC 091958
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 PM EDT MON APR 09 2018

VALID 00Z TUE APR 10 2018 - 00Z FRI APR 13 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE NORTHERN
ROCKIES...

A SHORTWAVE AND COLD FRONT WILL MOVE INTO THE PACIFIC NORTHWEST ON TUESDAY...WITH MOISTURE SPREADING INTO THE NORTHERN ROCKIES AS
WELL. SNOW LEVELS WILL BE HIGH WITH THIS INITIAL SYSTEM...BUT WILL
DROP AS COLDER AIR MOVES IN BEHIND IT. THUS WHEN THE STRONGER
TROUGH MOVES ASHORE ON WEDNESDAY WE SHOULD SEE MORE IN THE WAY OF
ACCUMULATING SNOWFALL IN THE MOUNTAINS. OVER THE NEXT THREE DAYS
WILL THUS HAVE MODERATE TO HIGH PROBABILITIES OF 8"+ OF SNOW
ACROSS THE HIGHER ELEVATIONS OF THE WA/OR CASCADES...THE WA
OLYMPICS...SOUTH INTO THE SIERRAS AND THE KLAMATH MOUNTAINS...AND
EAST INTO THE NORTHERN ROCKIES. LIGHTER ACCUMULATIONS ARE ALSO
POSSIBLE BY DAY 3 INTO THE MT PLAINS TO THE NORTHWEST OF A
DEVELOPING LOW PRESSURE SYSTEM.


...NORTHERN PLAINS INTO THE UPPER MS VALLEY AND NORTHERN GREAT
LAKES...

SHORTWAVE ENERGY MOVING INTO THE PACIFIC NORTHWEST MONDAY NIGHT
WILL TRAVERSE THE ROCKIES AND EJECT INTO THE PLAINS ON WEDNESDAY.
THIS ENERGY SHOULD HELP SPAWN A SURFACE LOW THAT WILL TRACK EAST
ACROSS THE UPPER MS VALLEY INTO THE GREAT LAKES. EXPECT THAT WE
WILL SEE A SWATH OF ACCUMULATING SNOWFALL NORTH OF THIS LOW. MODEL
SPREAD HAS BEEN QUITE LARGE WITH THIS FEATURE...WITH THE GFS/NAM
FURTHER SOUTH THAN THE ECMWF. HOWEVER NOTED THAT BOTH THE 12Z
ECMWF AND UKMET DID INDEED TREND A BIT SOUTH...WHICH WOULD
INCREASE THE SNOW THREAT OVER PORTIONS OF NORTHERN MN/WI/MI BY
LATER WEDNESDAY INTO EARLY THURSDAY. THINK WE WILL SEE A SWATH OF
2-4" ACROSS THIS AREA...ALTHOUGH THE EXACT AXIS TO BE IMPACTED
REMAINS UNCERTAIN...WITH MORE LOCALIZED 4-6" AMOUNTS POSSIBLE. WPC
KEPT OUR SNOWFALL AXIS GENERALLY IN THE MIDDLE OF THE MODEL SPREAD
(NORTH OF THE GFS AND A BIT SOUTH OF THE ECMWF). WARM BOUNDARY
LAYER TEMPERATURES MAY LOWER RATIOS ON THE SOUTHERN PERIPHERY OF
THE RAIN/SNOW LINE SO WAS HESITANT TO GO TOO FAR SOUTH WITH OUR
HIGHER AMOUNTS...BUT WILL NEED TO CONTINUE TO MONITOR TRENDS TO
SEE IF THE SOUTHWARD SHIFT CONTINUES.

SOME LIGHT ICING IS POSSIBLE ALONG THE TRANSITION ZONE ACROSS ND
AND THE NORTHERN GREAT LAKES...BUT NOT EXPECTING ANYTHING MAJOR
WITH ONLY A NARROW CORRIDOR POTENTIALLY FAVORABLE FOR ICE AND
MARGINAL SURFACE TEMPERATURES LIKELY LIMITING IMPACTS.

CHENARD




$$




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FOUS11 KWBC 100847
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
446 AM EDT TUE APR 10 2018

VALID 12Z TUE APR 10 2018 - 12Z FRI APR 13 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE NORTHERN
ROCKIES...

BY EARLY TUE...MODELS SHOW AN UPPER RIDGE BEGINNING TO GIVE WAY TO
A NEGATIVELY TILTED UPPER TROUGH LIFTING FROM THE EASTERN PACIFIC
INTO WESTERN CANADA AND PACIFIC NORTHWEST. LIGHT TO MODERATE
PRECIPITATION IS EXPECTED TO ACCOMPANY THE ASSOCIATED COLD FRONT
AS IT MOVES MOVES
ACROSS THE NORTHWEST INTO THE NORTHERN ROCKIES LATE TUE INTO EARLY
WED. SNOW LEVELS ARE EXPECTED TO BE QUITE HIGH AHEAD OF THE
FRONT...WITH ACCUMULATING SNOWS CONFINED MAINLY TO THE HIGHER
PEAKS OF THE NORTHERN CASCADES ON TUE. HOWEVER...POST-FRONTAL
ONSHORE FLOW ALONG WITH FALLING SNOW LEVELS MAY SUPPORT SOME HEAVY ACCUMULATIONS ACROSS THE OLYMPICS AND NORTHERN CASCADES BY EARLY
WED. THIS SYSTEM IS EXPECTED TO QUICKLY MOVE EAST...WITH SNOW
LEVELS RISING AHEAD OF THE NEXT SYSTEM APPROACHING THE COAST ON
WED. THIS NEXT SYSTEM IS EXPECTED TO BE STRONGER THAN THE
PREVIOUS...WITH SNOW LEVELS DROPPING DRAMATICALLY AS A DEEP UPPER
TROUGH AND ITS ASSOCIATED FRONT MOVE INLAND WED NIGHT. BY THU
MORNING...THE HEAVY SNOW THREAT IS EXPECTED TO EXTEND SOUTH INTO
THE SOUTHERN CASCADES...NORTHWEST CA COASTAL RANGES AND THE
NORTHERN SIERRA.

...NORTHERN PLAINS TO THE UPPER GREAT LAKES...

LEADING SHORTWAVE EMANATING FROM THE WESTERN U.S. IS EXPECTED TO
MOVE ACROSS THE REGION...SUPPORTING A STRIPE OF LIGHT TO MODERATE
SNOWS FROM EASTERN NORTH DAKOTA TO NORTHERN MICHIGAN. WPC DAY 2
PROBABILITIES (ENDING 12 UTC THU) SHOW A SLIGHT RISK FOR
ACCUMULATIONS OF 4-INCHES OR MORE ACROSS THE REGION.

...NORTHERN ROCKIES TO THE PLAINS...

MODELS SHOW THE SECOND SYSTEM ENTERING THE WEST CONTINUING TO
AMPLIFY AS IT MOVES ACROSS THE WESTERN U.S. ON THU WITH A CLOSED
LOW UPPER LOW DEVELOPING OVER THE CENTRAL HIGH PLAINS THU
NIGHT-FRI MORNING. STRONG EASTERLY LOW LEVEL INFLOW TO THE NORTH
OF A DEVELOPING POWERFUL SURFACE CYCLONE IS EXPECTED TO DIRECT
AMPLE MOISTURE INTO AN AREA OF STRONG LIFT SUPPORTED BY LOW TO MID
LEVEL FRONTOGENESIS AND AN UPPER JET COUPLET. BY FRI
MORNING...WIND-DRIVEN HEAVY SNOWS CAN BE EXPECTED ACROSS PORTIONS
OF THE NORTHERN HIGH PLAINS...WITH THE THREAT FOR HEAVY
ACCUMULATIONS INCREASING NEAR THE END OF THE PERIOD. WPC DAY 3
PROBABILITIES (ENDING 12 UTC FRI)...SHOW A SIGNIFICANT THREAT FOR
ACCUMULATIONS OF 8-INCHES OR MORE...WITH LOCALLY HEAVIER AMOUNTS
POSSIBLE ACROSS SOUTHEAST MONTANA BACK INTO THE CENTRAL AND
WESTERN RANGES. FURTHER EAST...RAIN IS EXPECTED TO CHANGE TO SNOW
ACROSS THE DAKOTAS...MARKING THE ONSET OF WHAT IS EXPECTED TO
BECOME A MAJOR WINTER STORM FOR THE REGION. REFER TO THE WPC
MEDIUM RANGE PRODUCTS FOR FURTHER DETAILS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA

$$




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FOUS11 KWBC 102025
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
425 PM EDT TUE APR 10 2018

VALID 00Z WED APR 11 2018 - 00Z SAT APR 14 2018


DAYS 1-3...

...WEST INTO NORTHERN HIGH PLAINS/UPPER MIDWEST...

A POWERFUL UPPER TROUGH AND DYNAMIC SHORT WAVE WITHIN THE LARGE
SCALE ANOMALY WILL PLOW INTO THE WEST COAST ON WED, SLICE THROUGH
THE INTER-MOUNTAIN WEST AND GREAT BASIN ON THURS BEFORE DEVELOPING
AS A DEEP CYCLONE OVER THE PLAINS LATE THURS INTO FRI. THE OVERALL
RESULTANT WILL BE HEAVY SNOWFALL FOR THE WESTERN TERRAIN AND A
POTENTIAL BLIZZARD ACROSS THE NORTHERN HIGH PLAINS. THE MAJORITY
OF THE MODEL GUIDANCE CAPTURES THIS LARGE SCALE SYSTEM RATHER WELL
WITH SPREAD ONLY SHOWING UP FRI, AS THE SYSTEM ARRIVES AND DEEPENS
OVER THE PLAINS. OVERALL WPC FAVORED THE SLOWER GUIDANCE, ECMWF
AND UKMET, RATHER THAN THE SLIGHTLY MORE PROGRESSIVE SOLUTIONS,
GFS AND NAM.

THE HEAVY SNOW ACROSS THE WEST ON WED WILL BE SOMEWHAT LIMITED TO
HIGHER ELEVATIONS DESPITE THE INCREASE IN PAC MOISTURE TRANSPORT.
HOWEVER, THE CRASHING LOWER HEIGHTS SHIFTING DOWNSTREAM ON THURS
WILL RESULT IN WIDESPREAD HEAVY SNOWFALL FROM THE WA/OR CASCADES
AND NORTHERN CA MTNS/SIERRA INTO MUCH OF THE INTER-MOUNTAIN WEST.
AS THE AMPLIFIED UPPER TROUGH AND CLOSING MID TO UPPER LOW REACHES
THE PLAINS ON FRI, A SIGNIFICANT AMOUNT OF GULF OF MEXICO MOISTURE
WILL BECOME CONSUMED BY THE LARGE CYCLONE. SO FROM THURS EVENING
THROUGH FRI EVENING, SIGNIFICANT SNOWFALL ACCUMULATIONS ARE
ANTICIPATED ACROSS WESTERN SD UP INTO SERN/SOUTH CENTRAL MT. ADD
IN THE AIR TEMP ALONG WITH THE STRONG NERLY WINDS AND BLIZZARD
CRITERIA MAYBE MET, PLUS ENHANCED UPSLOPE REGIME ESPECIALLY INTO
THE BLACK HILLS OF SD. OVERALL WPC PREFERRED ECMWF/UKMET THERMALS
OVER THE GFS/NAM.


...UPPER MS VALLEY AND GREAT LAKES...

UPPER DYNAMICS STREAMING INTO THE WEST TODAY WILL EMERGE OUT OVER
THE UPPER MIDWEST ON WED AND BECOME BETTER ORGANIZED, AS AN UPPER
JET ROUNDS THE STATIONARY UPPER VORTEX OVER UPPER CENTRAL CANADA.
EXPECT A RELATIVELY DEEP SURFACE LOW TO DEVELOP AND STREAK FROM
THE UPPER MS VALLEY THROUGH THE UPPER GREAT LAKES INTO NORTHERN
NEW ENGLAND LATE WED THROUGH THURS/VERY EARLY FRI. AS A RESULT...
INCREASING MOISTURE CONTENT AND DECENT FRONTOGENESIS WILL PRODUCE
A NARROW ZONE OF HEAVY SNOWFALL. THE CONSENSUS OF THE GUIDANCE
CAPTURES THIS ZONE FROM NERN ND THROUGH NORTHERN MN INTO THE UP OF
MI AND EVENTUALLY IN NORTHERN MAINE.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER

$$




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FOUS11 KWBC 110838
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 AM EDT WED APR 11 2018

VALID 12Z WED APR 11 2018 - 12Z SAT APR 14 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND NORTHERN CALIFORNIA...

AN AMPLIFYING UPPER TROUGH AND ASSOCIATED COLD FRONT ARE EXPECTED
TO MOVE INTO THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA WED
NIGHT...WITH SNOW LEVELS DROPPING SIGNIFICANTLY ACROSS THE REGION
BY THU MORNING. THIS WILL RAISE PROBABILITIES FOR LOCALLY HEAVY
SNOW AMOUNTS ACROSS THE OLYMPICS AND CASCADES TO THE NORTHWEST CA
COASTAL RANGES AND NORTHERN SIERRA. THE UPPER TROUGH IS EXPECTED
TO SHIFT FURTHER EAST ON THU...HOWEVER CONTINUED ONSHORE FLOW
AHEAD OF AN APPROACHING WARM FRONT WILL CONTINUE TO SUPPORT
LOCALLY HEAVY ACCUMULATIONS ACROSS THE OLYMPICS AND PORTIONS OF
THE CASCADES INTO FRI. BY LATE FRI...THE THREAT IS EXPECTED TO
WANE ACROSS THE SOUTHERN CASCADES AS AN UPPER RIDGE BEGINS TO
BUILD AHEAD OF THE NEXT APPROACHING SHORTWAVE -- PUSHING SNOW
LEVELS HIGHER AND DIRECTING DEEPER MOISTURE FURTHER NORTH INTO
NORTHWEST WA AND SOUTHERN BRITISH COLUMBIA.

...NORTHERN ROCKIES TO THE HIGH PLAINS AND UPPER MIDWEST...

THERE REMAINS A STRONG MODEL SIGNAL FOR THE DEVELOPMENT OF A
STRONG SPRING STORM...PRODUCING STRONG WINDS AND HEAVY SNOW
ACCUMULATIONS ACROSS PORTIONS OF THE NORTHERN ROCKIES...PLAINS AND
UPPER MIDWEST THU-SAT.

THE PREVIOUSLY NOTED TROUGH ENTERING THE WESTERN U.S. WED NIGHT IS
FORECAST TO CONTINUE AMPLIFYING AS IT MOVES ACROSS THE WESTERN
U.S. THU...WITH AN UPPER LOW CLOSING OFF OVER THE NORTHERN ROCKIES
BY FRI MORNING. SHORTWAVE ENERGY LIFTING ALONG THE LEADING EDGE
OF THE TROUGH...IN ADDITION TO LOW LEVEL FORCING ALONG THE
ASSOCIATED FRONTAL BAND...IS EXPECTED TO PRODUCE LOCALLY HEAVY
MOUNTAIN SNOWS FROM THE WASATCH NORTHWARD INTO THE WESTERN WY AND
MONTANA RANGES ON THU. HEAVIEST AMOUNTS ON THU INTO EARLY FRI ARE
EXPECTED CENTER FROM THE SOUTHWEST MONTANA RANGES EASTWARD INTO
THE ADJACENT HIGH PLAINS. GUIDANCE CONTINUES TO SHOW ENHANCED LOW
LEVEL CONVERGENCE AHEAD OF A WAVE LIFTING NORTHEAST INTO THE
REGION AND ALONG A LOW-MID LEVEL BAROCLINIC ZONE/TROUGH EXTENDING
TO THE NORTHWEST. WPC DAY 2 PROBABILITIES (ENDING 12 UTC FRI)
CONTINUE TO SHOW THE WIDESPREAD POTENTIAL FOR SNOW ACCUMULATIONS
OF 8-INCHES OR MORE...WITH LOCALLY HEAVIER AMOUNTS...ACROSS THE
REGION. BY FRI MORNING...THE HEAVY THREAT IS EXPECTED TO BEGIN
SHIFTING FURTHER SOUTH AND EAST ACROSS THE NORTHERN PLAINS AS A
POWERFUL SURFACE CYCLONE MOVES ACROSS THE CENTRAL PLAINS. STRONG
DIVERGENCE ALOFT AFFORDED BY AN UPPER JET COUPLET...ALONG WITH LOW
TO MID LEVEL FRONTOGENESIS...IS EXPECTED TO SUPPORT AN EXPANDING
AREA OF PRECIPITATION NORTHWEST OF THE LOW...WITH RAIN CHANGING TO
SNOW AS THE LOW PULLS COLDER AIR SOUTH THROUGH THE HIGH PLAINS.
OVERNIGHT GUIDANCE SHOWED HEAVIEST ACCUMULATIONS CENTERING OVER
WESTERN TO CENTRAL SOUTH DAKOTA WITH WPC DAY 3 PROBABILITIES
(ENDING 12 UTC SAT) SHOWING A MODERATE RISK FOR 8-INCHES AND
SLIGHT RISK FOR A FOOT OR MORE ACROSS THE REGION. THERE IS THE
POTENTIAL FOR HEAVY AMOUNTS EXTENDING FURTHER EAST ALONG A FRONTAL
BAND STRETCHING ACROSS THE UPPER MS VALLEY INTO THE UPPER GREAT
LAKES. EXPECT RAIN CHANGING TO SNOW ALONG THE NORTHERN EXTENT OF
THE PRECIPITATION SHIELD AS A SHORTWAVE TROUGH PIVOTING ACROSS
ONTARIO PUSHES COLDER FURTHER SOUTH INTO REGION ON FRI.

THE PROBABILITY OF SIGNIFICANT ICING (0.25 INCH OR MORE) IS LESS
THAN 10 PERCENT.

PEREIRA

$$




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FOUS11 KWBC 112033
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
432 PM EDT WED APR 11 2018

VALID 00Z THU APR 12 2018 - 00Z SUN APR 15 2018


DAYS 1-3...

...UPPER MS VALLEY AND GREAT LAKES...

UPPER DYNAMICS EMERGING THIS AFTERNOON/EVENING OUT OVER THE
NORTHERN PLAINS/UPPER MIDWEST BECOME BETTER ORGANIZED, AS THE
NORTHERN POLAR JET ROUNDS THE STATIONARY UPPER VORTEX OVER UPPER
CENTRAL CANADA. EXPECT A RELATIVELY DEEP SURFACE LOW TO STREAK
FROM THE UPPER MS VALLEY THROUGH THE UPPER GREAT LAKES INTO
NORTHERN NEW ENGLAND THROUGH THURS/VERY EARLY FRI. AS A RESULT...
INCREASING MOISTURE CONTENT AND DECENT FRONTOGENESIS WILL PRODUCE
A NARROW ZONE OF HEAVY SNOWFALL AND LIGHT ICING. THE CONSENSUS OF
THE GUIDANCE CAPTURES THIS ZONE FROM EASTERN ND THROUGH NORTHERN
MN INTO THE UP OF MI AND EVENTUALLY IN NORTHERN MAINE.

...WEST INTO HIGH PLAINS AND UPPER MIDWEST...

A CLASSIC MULTIPLE FACETED SPRING CYCLONE WILL IMPACT THE MIDDLE
OF THE COUNTRY LATE THIS WORK WEEK INTO THE WEEKEND FEATURING
WIDESPREAD HEAVY SNOW AND POSSIBLE FREEZING RAIN.

A POWERFUL UPPER TROUGH AND DYNAMIC SHORT WAVE WITHIN THE LARGE
SCALE ANOMALY WILL PLOW INTO THE WEST COAST THIS
AFTERNOON/EVENING, SLICE THROUGH THE INTER-MOUNTAIN WEST AND GREAT
BASIN ON THURS BEFORE DEVELOPING AS A DEEP CYCLONE OVER THE PLAINS
LATE THURS INTO FRI AND THROUGH SAT. THE OVERALL RESULTANT WILL BE
HEAVY SNOWFALL FOR THE WESTERN TERRAIN AND A LIKELY BLIZZARD
ACROSS THE NORTHERN HIGH PLAINS. THE MAJORITY OF THE MODEL
GUIDANCE CAPTURES THIS LARGE SCALE SYSTEM RELATIVELY WELL WITH
LESS SPREAD THAN 24 HRS AGO. OVERALL WPC FAVORED THE MIDDLE OF THE
ROAD SOLUTION OR UKMET/ECMWF MEAN AND GEFS MEAN PER MASS FIELDS.
THE ECMWF REMAINS SLIGHTLY SLOWER AND GFS SLIGHTLY MORE
PROGRESSIVE.

THE CRASHING LOWER HEIGHTS MOVING THROUGH THE WEST ON THURS WILL
RESULT IN WIDESPREAD HEAVY SNOWFALL FROM THE WA/OR CASCADES AND
NORTHERN CA MTNS/SIERRA INTO MUCH OF THE INTER-MOUNTAIN WEST. AS
THE AMPLIFIED UPPER TROUGH AND CLOSING MID TO UPPER LOW REACHES
THE PLAINS ON FRI, A SIGNIFICANT AMOUNT OF GULF OF MEXICO MOISTURE
WILL BECOME CONSUMED BY THE LARGE CYCLONE. SO FROM THURS EVENING
THROUGH FRI EVENING, SIGNIFICANT SNOWFALL ACCUMULATIONS ARE
ANTICIPATED ACROSS WESTERN SD UP INTO SERN/SOUTH CENTRAL MT. ADD
IN THE AIR TEMP ALONG WITH THE STRONG NERLY WINDS AND BLIZZARD
CRITERIA WILL LIKELY BE MET, PLUS ENHANCED UPSLOPE REGIME
ESPECIALLY INTO THE BLACK HILLS OF SD. FINALLY ON SAT, THE CYCLONE
WILL CRAWL DOWNSTREAM, OCCLUDE AND DEPART THE FRONT RANGE OF THE
ROCKIES INTO THE MID MS VALLEY. STRONG DYNAMIC COOLING OF THE NWRN
QUAD OF THE SYSTEM SHOULD HELP ESTABLISH A WELL-DEVELOPED AND
PERSISTENT TROWAL. THE HEAVIEST SNOWS WILL OCCUR FROM NORTHERN
CENTRAL NE UP INTO SERN SD AND ACROSS SOUTHERN MN INTO WI. ALSO ON
FRI AND SAT, EXPECT A POSSIBLE TRANSITION ZONE OF SLEET-FREEZING
RAIN TO SET UP FROM SERN SD THROUGH SOUTHERN MN/NORTHERN IA INTO
WI AND PARTS OF MI, AS ANOMALOUS SURFACE HIGH PRESSURE WEDGES IN
FROM THE NORTH. OVERALL WPC PREFERRED AN ENSEMBLE APPROACH TO
THERMALS EACH DAY.

MUSHER

$$




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FOUS11 KWBC 120816
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
415 AM EDT THU APR 12 2018

VALID 12Z THU APR 12 2018 - 12Z SUN APR 15 2018


DAYS 1-3...

A MAJOR WINTER STORM IS EXPECTED OVER THE NORTHERN PLAINS AND
UPPER MS VALLEY WITH AREAS OF HEAVY SNOW AND FREEZING RAIN...AND
POSSIBLE BLIZZARD CONDITIONS...

...NORTHERN ROCKIES/GREAT BASIN ACROSS NORTHERN PLAINS...UPPER MS
VALLEY AND GREAT LAKES/NORTHERN NEW YORK...

DAY 1...THU/THU NIGHT...

A POWERFUL UPPER TROUGH AND DYNAMIC SHORT WAVE WILL MOVE EAST
ACROSS THE NORTHERN ROCKIES AND GREAT BASIN EAST INTO THE NORTHERN
HIGH PLAINS. PEAK 700 MB CONVERGENCE DEPARTS NORTHWEST MT ACROSS
CENTRAL MT WITH THE CIRCULATION AND ALSO DOWNSTREAM OVER SOUTHEAST
MT AND THE DAKOTAS ON THE DOWNSTREAM WARM FRONT. HEAVY SNOWFALL
IS CENTERED OVER THE LONGER DURATION CONVERGENCE OVER SOUTHEAST
MT...WITH SECONDARY MAXIMA IN THE WA/OR CASCADES AND ALONG THE
TRAILING FRONT CROSSING WESTERN WY AND NORTHERN UT. THE MODELS ARE
STARTING TO CONVERGE ON A COMMON SOLUTION...SUPPORTING A CONSENSUS
BASED APPROACH. WPC FAVORED THE MIDDLE OF THE ROAD SOLUTION OR
UKMET/ECMWF MEAN AND GEFS MEAN.

DAY2...FRI-FRI NIGHT...

AS THE AMPLIFIED UPPER TROUGH AND CLOSING MID TO UPPER LOW REACHES
THE PLAINS ON FRI, A SIGNIFICANT AMOUNT OF GULF OF MEXICO MOISTURE
WILL BECOME ADVECTED NORTH INTO THE COLD SECTOR OF THE CYCLONE.
AS THE UPPER TOUGH MOVES OUT OF THE HIGH PLAINS ACROSS THE
NORTHERN AND CENTRAL PLAINS...UPPER DIVERGENCE MAXIMA AND MID
LEVEL FRONTOGENESIS/THETA-E ADVECTION MAXIMA FOCUS HEAVY SNOW
POTENTIAL IN SOUTHERN/EASTERN SOUTH DAKOTA TO ADJACENT NORTHERN
NEBRASKA. HEIGHT FALLS LEAD TO TEMPERATURE DROPS WITH RAIN
CHANGING TO SNOW IN MUCH OF SOUTHEAST WY TO WESTERN AND NORTHERN
NE/NORTHEAST CO/NORTHWEST KS. MOISTURE ALOFT INCREASES IN THE
COLD SECTOR WITH WARM FRONTAL LIFT PRODUCING MIXED PRECIP
(SLEET/FREEZING RAIN) IN SOUTHEAST MN TO CENTRAL WI...BECOMING
SNOW IN CENTRAL MN TO NORTHERN WI AND THE UP OF MI.


DAY 3...SAT-SAT NIGHT...

ON SAT, THE CYCLONE DRIFTS EAST FROM IS ACROSS IL AND IN. A STRONG
1040 MB HIGH NORTH UP IN HUDSON BAY PROVIDES REINFORCEMENT OF COLD
AIR ACROSS THE UPPER GREAT LAKES...WITH SNOW CONTINUING IN
SOUTHEAST MN/NORTHERN WI/UP OF MI IN WELL-DEVELOPED AND PERSISTENT
TROWAL. EXPECT A POSSIBLE TRANSITION ZONE OF SLEET-FREEZING RAIN
TO SET UP FROM THROUGH SOUTHERN WI/ CENTRAL TO NORTHERN LOWER
MI...POSSIBLY EXTENDING DOWNSTREAM INTO PARTS OF WESTERN AND
NORTHERN NEW YORK TO NORTHERN VT. THE POSSIBILITY OF MULTIPLE
PRECIP TYPES ELEVATES THE UNCERTAINTY ACROSS SOUTHERN WI/LOWER
MI/WESTERN TO NORTHERN NY/VT.

THE PROBABILITY OF SIGNIFICANT ICING (0.25 INCHES) IS LESS THAN 10
PERCENT ON DAY 1...BUT AN ENHANCED RISK IS SHOWN OVER PORTIONS OF
SOUTHERN WI DAY 2 AND CENTRAL LOWER MI DAY 2 AND ON DAY 3.

...WA CASCADES/OLYMPICS DAYS 2/3...

A SLOW CYCLONIC CIRCULATION IS FORECAST TO DRIFT EAST SOUTHEAST
ACROSS THE NORTH PACIFIC. A DOWNSTREAM UPPER JET MAXIMA MOVES
ONSHORE DAY 2 ACROSS VANCOUVER ISLAND AND THEN WA STATES. UPPER
DIVERGENCE MAXIMA WITHIN THE MOIST SOUTHWEST FLOW IS FORECAST TO
BRING WIDESPREAD PRECIPITATION WITH LOCALLY HEAVY SNOW POSSIBLE IN
THE NORTHERN WA CASCADES. HEIGHTS AND TEMPERATURES ALOFT BEGIN TO
DECLINE DAY 3 AS THE CIRCULATION DRAWS NEARER...SO SEVERAL
ADDITIONAL INCHES OF SNOW ARE POSSIBLE IN THE WA CASCADES. THE
STRENGTH OF THE LIFT DECLINES LATER SAT NIGHT AS THE JET MAXIMA
MOVES FURTHER SOUTH ACROSS OR INTO CA BY SUN MORNING.

PETERSEN


$$




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FOUS11 KWBC 122016
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
415 PM EDT THU APR 12 2018

VALID 00Z FRI APR 13 2018 - 00Z MON APR 16 2018


DAYS 1-3...

A CLASSIC AND MAJOR MULTI-FACET SPRING STORM FEATURING WIDESPREAD
HEAVY SNOW AND TRANSITION ZONE WILL IMPACT MUCH OF THE MIDWEST
FRIDAY THROUGH THE WEEKEND.

A POWERFUL UPPER TROUGH AND DYNAMIC SHORT WAVE WITHIN THE LARGE
SCALE NEG ANOMALY IS ADVANCING THROUGH THE WEST THIS AFTERNOON AND
WILL LATER EJECT OUT INTO THE HIGH PLAINS LATER THIS EVENING INTO
THE OVERNIGHT HRS. A SYNOPTIC SCALE DEEP CYCLONE WILL FORM AND
SLIDE VERY SLOWLY DOWNSTREAM, ONLY REACHING THE GREAT LAKES BY SUN
EVENING. THE OVERALL RESULTANT WILL BE HEAVY SNOWFALL FOR THE
FRONT RANGE OF THE NORTHERN TO CENTRAL ROCKIES THROUGH THE UPPER
MIDWEST INTO THE UPPER GREAT LAKES WITH LIKELY BLIZZARD CONDITIONS
ACROSS WESTERN AND CENTRAL PORTIONS OF SD AND NE. THE MAJORITY OF
THE MODEL GUIDANCE CAPTURES THIS LARGE SCALE SYSTEM RELATIVELY
WELL WITH SMALL SPREAD. OVERALL WPC FAVORED A SLOWER SOLUTION OR ECMWF/UKMET/ECMWF MEAN AND GEFS MEAN PER MASS FIELDS. THE GFS
REMAINS SLIGHTLY MORE PROGRESSIVE AND AN OUTLIER AT THE MOMENT.

THE AMPLIFIED UPPER TROUGH AND CLOSING MID TO UPPER LOW MOVES INTO
THE PLAINS ON FRI, A SIGNIFICANT AMOUNT OF GULF OF MEXICO MOISTURE
WILL BE CONSUMED BY THE LARGE LOW PRESSURE SYSTEM. SO FROM THURS
EVENING THROUGH FRI EVENING, SIGNIFICANT SNOWFALL ACCUMULATIONS
ARE ANTICIPATED ACROSS WESTERN NE/SD UP INTO SERN/SOUTH CENTRAL
MT. ADD IN NEAR FREEZING TEMPS ALONG WITH THE STRONG NERLY WINDS
AND BLIZZARD CRITERIA WILL BE MET, PLUS ENHANCED UPSLOPE REGIME
ESPECIALLY INTO THE BLACK HILLS OF SD SOUTH INTO NE WILL BE
PUMMELED. THEN ON SAT, THE CYCLONE WILL CRAWL DOWNSTREAM THROUGH
THE MID MS VALLEY, WHILE OCCLUDING. STRONG DYNAMIC COOLING OF THE
NWRN QUAD OF THE SYSTEM SHOULD HELP ESTABLISH A WELL-DEVELOPED AND
ALMOST STATIONARY TROWAL AND DEFORMATION ZONE. THE HEAVIEST SNOWS
WILL BE POSSIBLE FROM NORTH CENTRAL NE TO SERN SD AND SWRN MN/NWRN
IA. FINALLY ON SUN, THE TRIPLE POINT LOW WILL LIFT UP INTO MI AND
SNOW REMAINS POSSIBLE FROM MI INTO THE UPPER MS VALLEY, ESPECIALLY
OVER THE UP OF MI. ALSO, EXPECT A POSSIBLE TRANSITION ZONE OF
SLEET-FREEZING RAIN TO SET UP FROM SERN SD THROUGH SOUTHERN
MN/NORTHERN IA INTO PARTS OF WI/MI AND UPSTATE NY/NORTHERN NEW
ENGLAND. THESE TYPE OF SYSTEMS TYPICALLY FEATURE MAINLY RAIN TO
SNOW WITH PERHAPS A NARROW TRANSITION ZONE, BUT THIS ZONE COULD BE
MORE EXTENSIVE AS A ANOMALOUS SURFACE HIGH PRESSURE WEDGES IN
FROM THE NORTH. OVERALL WPC PREFERRED AN ENSEMBLE APPROACH TO
THERMALS EACH DAY AND BY THE END OF THE WEEKEND, THIS COULD BE A
HISTORICAL STORM.

MUSHER


$$




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FOUS11 KWBC 130820
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
419 AM EDT FRI APR 13 2018

VALID 12Z FRI APR 13 2018 - 12Z MON APR 16 2018


DAYS 1-3...

...NORTHERN TO CENTRAL PLAINS/UPPER MS VALLEY/GREAT LAKES NEW
YORK/NEW ENGLAND...

WIDESPREAD HEAVY SNOW EXPECTED OVER SD..NE...AND SOUTHERN MN WITH
MESSY MULTIPLE PRECIP TYPES ACROSS THE GREAT LAKES TO NEW YORK AND
NEW ENGLAND FRIDAY THROUGH THE WEEKEND.

DAY 1...
THE MODELS FORECAST THE DEVELOPMENT OF A CLOSED 700 MB LOW OVER
NEBRASKA THAT MOVES SLOWLY EAST SOUTHEAST ACROSS THE STATE AND
ADJACENT KS. THE HEIGHT FALLS WITH THE LOW DEVELOPING CAUSES
TEMPERATURES OVER THE CENTRAL TO NORTHERN PLAINS TO DROP...WITH
PRECIP CHANGING TO SNOW ACROSS SD/NE/EASTERN CO/NORTHWEST KS. AS A
STRONG DEFORMATION ZONE SETS UP AND PERSISTS NEAR THE SD/NE
BORDER...HEAVY SNOW IS EXPECTED IN THIS AREA WITH A FOOT TO 18
INCHES POSSIBLE IN SOUTH CENTRAL SD TO ADJACENT NORTH CENTRAL NE.

THE TRICKIER ASPECT OF THE FORECAST IS FURTHER NORTH WITH A TIGHT
PRECIPITATION GRADIENT ON THE NORTH EDGE OF THE PRECIP SHIELD IN
NORTHERN SD NEAR THE ND BORDER AND CENTRAL MN/NORTHERN WI/UP OF MI
AS COLD DRY AIR FILTERS SOUTH FROM CANADA INTO THESE AREAS.

FURTHER SOUTHEAST...THE SHORTER DURATION OF SNOW IN EASTERN
NEBRASKA/SOUTHEAST SD/SOUTHEAST MN/SOUTHERN WI LEAD TO LIGHTER
AMOUNTS. WITHIN THE PRECIP TYPE TRANSITION ZONE A PERIOD OF MIXED SLEET/FREEZING RAIN IS POSSIBLE IN THESE LOCATIONS...WITH LIGHT
AMOUNTS OF MIXED FROZEN PRECIP POSSIBLY EXTENDING AS FAR SOUTH AS
NORTHERN IOWA.

...DAY 2...

THE MODELS FORECAST THE 700 MB LOW TO MOVE SLOWLY EAST FROM NEAR
THE KS/NE BORDER ACROSS NORTHERN MO. THE MID LEVEL DEFORMATION
MAXIMA DRIFTS EAST OUT OF SD/NORTHEAST NE ACROSS SOUTHERN MN AND
NORTHERN WI...SO THIS WILL BE THE TARGETED AREA FOR BANDS OF
LOCALLY HEAVY SNOW.

AS HIGH PRESSURE BUILDS ACROSS SOUTHERN CANADA WITH A 1040 MB HIGH
THERE...COLD AIR FILTERS SOUTH ACROSS THE UPPER MS VALLEY AND
LAKES INTO NEW YORK ND NEW ENGLAND SAT.
PRECIP OF MULTIPLE TYPES IS EXPECTED ACROSS NORTHERN IL TO LOWER MI...CONTINUING IN WESTERN AND NORTHERN NY AND ADJACENT WESTERN
NEW ENGLAND. SIGNIFICANT ACCUMULATIONS OF A HALF INCH OF MIXED
SLEET AND FREEZING RAIN ARE POSSIBLE IN LOWER MI TO
WESTERN/NORTHERN NY.
LOW CONFIDENCE EXISTS IN THE AMOUNTS DUE TO QPF BEING SPLIT UP
INTO MULTIPLE PRECIP TYPES.

OVERALL WITH THE GFS BEING WARMER AND TRENDING COLDER...MORE
WEIGHTING WAS GIVEN TO THE COLDER SREF/NAM/ECMWF FORECASTS.

...DAY 3...

ON SUN-SUN NIGHT, THE TRIPLE POINT LOW WILL LIFT UP INTO MI AND
SNOW REMAINS POSSIBLE NORTHWEST OF THE LOW IN NORTHERN WI TO THE
UP OF MI.
HOW FAR NORTH INTO MI LOW PRESSURE DEVELOPS WILL HELP DETERMINE
THE NORTHWEST EXTENT OF HEAVY SNOW ON DAY 3 AS THE GFS/UKMET DO
NOT EXTEND THE SNOW AXIS AS FAR WEST AS THE NAM/ECMWF/SREF MEAN.

DOWNSTREAM....MID LEVEL WARM ADVECTION OVER THE DAMMED COLD AIR
OVER WESTERN AND NORTHERN NY AND MUCH OF INTERIOR NEW ENGLAND
CONTINUES TO LEAD TO A MIXED SLEET/FREEZING RAIN
EPISODE...GRADUALLY EXPANDING SOUTH INTO NORTHEAST PA. VEERING
FLOW LEADS TO A GRADUAL WARMUP IN NEW YORK/INTERIOR NEW
ENGLAND..LIKELY POINTING TOWARDS LESS SLEET AND IN SOME CASES
MIXING BACK WITH FREEZING RAIN AND RAIN. ACCUMULATIONS OF ICE ARE
POSSIBLE ON EXPOSED SURFACES IN NORTHERN NY/VT/NH/INTERIOR MAINE
AND IN LOWER MI. THE WARM INVERSION ALOFT ABOVE FREEZING PREVENTS
MUCH ACCUMULATING SNOW ON DAY 3 IN INTERIOR NY/NEW ENGLAND.


...PACIFIC NORTHWEST/CALIFORNIA...

A SLOW CYCLONIC CIRCULATION IS FORECAST TO DRIFT EAST SOUTHEAST
ACROSS THE NORTH PACIFIC. A DOWNSTREAM UPPER JET MAXIMA MOVES
ONSHORE FRI ACROSS VANCOUVER ISLAND AND THEN WA STATE BY SAT
MORNING. UPPER DIVERGENCE MAXIMA WITHIN THE MOIST SOUTHWEST FLOW
IS FORECAST TO
BRING WIDESPREAD PRECIPITATION WITH LOCALLY HEAVY SNOW LIKELY IN
THE NORTHERN WA CASCADES.
THE MULTI-MODEL ENSEMBLE NOW IS CONVERGING ON POTENTIAL FOR A FOOT
OF SNOW IN THE HIGHER ELEVATIONS OF THE NORTHERN WA CASCADES.
HEIGHTS AND TEMPERATURES ALOFT BEGIN TO DECLINE DAY 2 AS THE
CIRCULATION DRAWS NEARER...SO SEVERAL ADDITIONAL INCHES OF SNOW
ARE POSSIBLE IN THE WA CASCADES. THE JET DRIFTS SOUTH ACROSS OR
AND THEN INTO CA BY 12Z SUN. UPPER DIVERGENCE MAXIMA IN THE
VICINITY OF THE UPPER JET COMBINE WITH MOIST ONSHORE FLOW TO
PRODUCE SNOW IN THE HIGHER ELEVATIONS OF THE RANGES OF SOUTHWEST
OR/NORTHERN CA AND INTO THE CA SIERRA NEVADA RANGE. THE SLOW
MOVEMENT OF THE JET CORE COULD LEAD TO LOCALLY HEAVY SNOW IN THE
MOUNTAINS OF THE SHASTA/SISKIYOUS/CASCADE OF SOUTHERN
OR/NORTHWESTERN CA.

PETERSEN


$$




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FOUS11 KWBC 132133
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
533 PM EDT FRI APR 13 2018

VALID 00Z SAT APR 14 2018 - 00Z TUE APR 17 2018


DAYS 1-3...

...NORTHERN TO CENTRAL PLAINS/UPPER MS VALLEY/GREAT LAKES NEW
YORK/NEW ENGLAND...

WIDESPREAD HEAVY SNOW EXPECTED OVER SD...NE...AND SOUTHERN MN WITH
MESSY MULTIPLE PRECIP TYPES ACROSS THE GREAT LAKES TO NEW YORK AND
NEW ENGLAND FRIDAY THROUGH THE WEEKEND. SIGNIFICANT ICE AND SLEET
ACCUMULATIONS ARE EXPECTED FROM SRN WI...LOWER MI INTO UPSTATE NY
AND NRN NEW ENGLAND.

...DAY 1...

A CLOSED MID-LEVEL LOW WILL TRACK THROUGH THE CNTRL PLAINS INTO
THE MIDWEST TONIGHT/SATURDAY AS AN ATTENDANT SURFACE LOW SLOWLY
EDGES EAST FROM THE ERN NE/KS BORDER. A STRONG STATIONARY FRONT
CURRENTLY EXTENDING EAST OF THE SURFACE LOW...FROM WEST TO EAST
ACROSS THE MID-MS VALLEY AND SRN NEW ENGLAND...WILL SLOWLY DROP
SOUTH AS A COLD FRONT THROUGH SATURDAY AS A 1040+ MB HIGH SITS
OVER ONTARIO...ASSOCIATED WITH AN ANOMALOUSLY COLD AIR MASS FOR
MID-APRIL.

HEAVY SNOW IS STILL ON TRACK FOR NE INTO SERN SD INTO SRN MN AND
WI AS AN ONGOING DEFORMATION AXIS PIVOTS EWD AND LOW LEVEL TEMPS
CONTINUE TO COOL ACROSS THE UPPER MS VALLEY. LIFT SHOULD BE
ENHANCED WITH LEFT EXIT REGION UPPER LEVEL JET DYNAMICS AND
INCREASING UPPER LEVEL DIFFLUENCE AS THE CLOSED LOW SHIFTS EWD.

THERE WAS GOOD AGREEMENT FROM THE MODELS ON MASS FIELD DETAILS
THROUGH DAY 1 (00Z/15) BUT A REGION OF MIXED P-TYPES IS WHERE THE
GREATEST UNCERTAINTY LIES THROUGH DAY 1 ACROSS THE MS VALLEY INTO
LOWER MICHIGAN AND UPSTATE NY. THE NAM WAS COLDEST IN THE NEAR
SURFACE LAYER WITH THE SREF MEAN NEXT COLDEST...WITH THE GFS
WARMEST. WHILE THE NAM TYPICALLY IS BEST AT THE HANDLING OF
SHALLOW COLD AIR LAYERS NEAR THE SURFACE...TYPICAL EXTREME
TEMPERATURE BIASES IN THE NAM WERE A CONSIDERATION ALONG WITH
EARLY MORNING OBSERVATIONS WARMER THAN PREVIOUS NAM FORECASTS
ACROSS THE PLAINS. THEREFORE...A BLENDED APPROACH FOR THERMALS WAS
USED LED BY A MIXTURE OF NAM/SREF/GFS/EC.

FORECASTS SOUNDINGS ACROSS WI SHOWED THE POTENTIAL FOR A NARROW
SWATH OF HEAVY ICING WITH SLEET/FREEZING RAIN MIXTURE TO THE NORTH
(CENTRAL WI) AND SNOW OVER NRN WI.

...DAY 2...

THE CLOSED MID-LEVEL LOW OVER THE CENTER OF THE COUNTRY WILL
CONTINUE EAST SATURDAY THROUGH SUNDAY NIGHT WITH AN ELONGATION
FORECAST FROM SOUTH TO NORTH...WHILE THE TROUGH AXIS ACROSS THE
SOUTH ACQUIRES A NEGATIVE TILT WHILE SWINGING INTO THE SOUTHEAST.
A DRY SLOT IS EXPECTED TO POKE UP INTO THE UPPER MIDWEST ON SUNDAY
WITH THE HEAVIEST LIFT JUST EAST OF THE DRY SLOT...EVENTUALLY
CUTTING OFF BETTER MOISTURE FROM REACHING THE REMNANT COMMA HEAD
OVER THE MIDWEST. A CONVECTIVE ELEMENT TO THE PRECIPITATION ADDS
AN EXTRA CHALLENGE TO MIXED P-TYPE AMOUNTS ACROSS SRN LOWER
MICHIGAN INTO IL/IN/NWRN OH.

THE NAM BEGINS TO STRAY FROM THE PREFERRED CONSENSUS DURING THE
DAY 2 TIME FRAME AS ITS MID-LEVEL LOW BECOMES DISPLACED TO THE
SOUTH WHICH RESULTS IN COLDER TEMPERATURES TO THE SOUTH...MORE SO
THAN WHAT WOULD BE FORECAST IF THE NAM SHOWED MASS FIELD AGREEMENT
WITH THE REMAINING MODEL GUIDANCE. GIVEN THE NAM TENDS TO HAVE THE
BETTER HANDLING OF THE NEAR-SFC COLD LAYER...AND THE GFS TENDS TO
BE TOO WARM WITH 2 METER TEMPERATURES...A BLENDED APPROACH WAS
CONTINUED TO BE USED BUT CONFIDENCE CONTINUES TO BE LOW WITH THE
MIXED P-TYPE TRANSITION. NONETHELESS...THE MODEL CONSENSUS WAS FOR SIGNIFICANT...0.25 TO 0.50+ FREEZING RAIN ICE ACCUMULATIONS ACROSS
LOWER MI. IT IS LIKELY THAT HEAVIER 1-HR RAINFALL RATES WILL NOT
ALL TRANSLATE TO EQUAL ICE ACCRETION SO STAYED SOMEWHAT
CONSERVATIVE COMPARED TO SOME OF THE MODEL ICE FORECASTS FROM SRN
WI INTO LOWER MI AND EVEN PORTIONS OF UPSTATE NY.

MEANWHILE...HEAVY SNOW WILL LIKELY CONTINUE INTO NRN WI AND THE
U.P. OF MICHIGAN WITH A BLEND OF THE 12Z GFS/00Z ECMWF USED FOR
THERMALS FOLLOWING 100% WPC QPF FOR LIQUID EQUIVALENTS.

ACROSS THE NORTHEAST...IT APPEARS THAT A A COLD WEDGE WILL ALLOW A
MIXTURE OF SLEET AND FREEZING RAIN WITH FORECAST SOUNDINGS
INDICATING HEAVY SLEET ACCUMULATIONS GIVEN POTENTIALLY SUFFICIENT
REFREEZING LAYER DEPTH BUT TEMPERATURES PEAKING NEAR OR ABOVE +5 C
IN THE 850-700 MB LAYER. UNCERTAINTIES ALSO IN PLAY WITH SHALLOWER
NEAR-SFC REFREEZING LAYERS TO THE SOUTH AND 2 METER TEMPERATURES
ABLE TO SUPPORT FREEZING RAIN GIVEN THE TIME OF YEAR AND HIGHER
SUN ABLE OF MID-APRIL DURING THE DAY ON SUNDAY.

...DAY 3...

STARTING SUN NIGHT...THE MAIN CONCERN WILL BE FREEZING RAIN/SLEET
ACROSS NEW ENGLAND WITH ANY LINGERING SNOW ON THE BACK SIDE OF THE
LOW EXPECTED TO BE LIGHT IN NATURE ACROSS THE GREAT LAKES REGION.
AGAIN...NOT FOLLOWING THE NAM AT ALL FOR DAY 3 GIVEN DIFFERENCES
IN SYNOPTIC EVOLUTION COMPARED TO THE PREFERRED GFS/ECMWF COMBO
RESULTS IN A LOWER THAN AVERAGE FORECAST FOR DAY 3 ACROSS THE
NORTHEAST. AS STRONG WARM ADVECTION CONTINUES TO ERODE THE NEAR
SURFACE COLD WEDGE...AM EXPECTING A SLEET AND/OR FREEZING RAIN
MIXTURE TO TRANSITION TO ALL RAIN FOR MUCH OF THE NORTHEAST DURING
THE DAY ON MONDAY EXCEPT FOR PERHAPS THE FAR NRN EDGE OF NEW
HAMPSHIRE INTO MAINE.

...PACIFIC NORTHWEST/CALIFORNIA...

A SLOW CYCLONIC CIRCULATION IS FORECAST TO DRIFT EAST SOUTHEAST
ACROSS THE NORTH PACIFIC THROUGH THE WEEKEND. CONCERNS FOR HEAVIER
COVERAGE AND AMOUNTS OF SNOW RAMP UP SUNDAY INTO MONDAY AS COLDER
AIR FILTERS IN BEHIND THE STRONG PACIFIC COLD FRONT. THE LEFT EXIT
REGION OF A MID-UPPER LEVEL JET ROUNDING THE BASE OF THE CLOSED
LOW IS EXPECTED TO ENHANCE LIFT ACROSS THE INTERIOR NORTHWEST
ALONG WITH INCREASING UPPER DIFFLUENCE. HEAVY SNOW...10+
INCHES...IS EXPECTED FOR THE HIGHER ELEVATIONS OF SRN OR INTO NRN
CA AS WELL AS THE SIERRA NEVADA RANGE. A BLEND OF THE GFS/ECMWF
WAS USED FOR THIS SYSTEM GIVEN THEIR BLENDED PLACEMENT IN THE
MIDDLE OF THE LATEST SPREAD.

OTTO


$$




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FOUS11 KWBC 140817
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
416 AM EDT SAT APR 14 2018

VALID 12Z SAT APR 14 2018 - 12Z TUE APR 17 2018


DAYS 1-3...

...NORTHERN TO CENTRAL PLAINS/UPPER MS VALLEY/GREAT LAKES NEW
YORK/NEW ENGLAND...

HEAVY SNOW IS EXPECTED OVER NORTHEAST NE...NORTHWEST
IA...SOUTHEAST SD...SOUTHERN MN..AND NORTHERN WI/UP OF MI WITH
MESSY MULTIPLE PRECIP TYPES FROM SOUTHERN WI ACROSS THE GREAT
LAKES TO NEW YORK AND NEW ENGLAND. SIGNIFICANT ICE AND SLEET
ACCUMULATIONS ARE EXPECTED FROM SRN WI...LOWER MI INTO UPSTATE NY
AND NRN NEW ENGLAND.

...DAY 1 SAT...

HEAVY SNOW IS STILL ON TRACK FOR NE INTO SERN SD INTO SRN MN AND
NORTHERN WI AS AN ONGOING DEFORMATION AXIS PIVOTS NEWD AND LOW
LEVEL TEMPS CONTINUE TO COOL ACROSS THE UPPER MS VALLEY. LIFT
SHOULD BE ENHANCED WITH LEFT EXIT REGION UPPER LEVEL JET DYNAMICS.

A REGION OF MIXED P-TYPES IS WHERE THE GREATEST UNCERTAINTY LIES
THROUGH DAY 1 ACROSS SOUTHERN WI INTO LOWER MICHIGAN AND UPSTATE
NY AND VT. THE NAM WAS COLDEST IN THE BOUNDARY LAYER WITH THE
ECMWF AND SREF MEAN NEXT COLDEST...AND THE GFS WARMEST AND GIVEN
LESS WEIGHT AS A RESULT OF THE STRONG 1044 MB HIGH IN EASTERN
CANADA IN PLACE TO ADVECT COLD AIR INTO THE NORTHEAST. HALF TO ONE
INCH LIQUID EQUIVALENT IS FORECAST IN THE FORM OF ICE PELLETS IN
NORTHERN NY TO CENTRAL VT...A RARITY FOR MID APRIL.

FORECAST SOUNDINGS ACROSS WI/LOWER MI SHOWED THE POTENTIAL FOR A
NARROW SWATH OF HEAVY ICING WITH SLEET/FREEZING RAIN MIXTURE TO
THE NORTH (CENTRAL AND SOUTHERN WI) AND SNOW OVER NRN WI. THE
MODEL CONSENSUS WAS FOR SIGNIFICANT...0.25 TO 0.50+ FREEZING RAIN
ICE ACCUMULATIONS ACROSS LOWER MI INTO WESTERN NY. HEAVIER
RAINFALL RATES WILL LED TO RUNOFF AND NOT TO LEAD TO ICE ACCRETION
SO STAYED SOMEWHAT CONSERVATIVE COMPARED TO SOME OF THE MODEL ICE
FORECASTS FROM SRN WI INTO LOWER MI AND WESTERN TO CENTRAL NY.

...DAY 2 SUN...

HEAVY SNOW WILL LIKELY CONTINUE INTO NRN WI AND THE U.P. OF
MICHIGAN WITH A PERSISTENT BAND OF MID LEVEL DEFORMATION MOVING
NORTHEAST ACROSS NORTHERN WI INTO THE CENTRAL AND EASTERN UP OF
MI. MANUAL PROGS USED A BLEND OF THE 12Z ECMWF/00Z NAM/21Z SREF
MEAN FOR TEMPERATURE PROFILES.

ACROSS THE NORTHEAST...IT APPEARS THAT COLD AIR DAMMING WILL ALLOW
A MIXTURE OF SLEET AND FREEZING RAIN WITH FORECAST SOUNDINGS
INDICATING HEAVY SLEET ACCUMULATIONS IN NORTHERN NY AND VT GIVEN A
SUBFREEZING LAYER SEVERAL DEGREES COOLER THAN FREEZING BUT
TEMPERATURES PEAKING NEAR OR ABOVE +5 C IN THE 850-700 MB LAYER.
UNCERTAINTIES ALSO IN PLAY WITH CHANGING TEMPERATURES RESULTING IN
A MIXTURE OF PRECIP TYPES...WITH SLEET CHANGING TO FREEZING
RAIN...AND PLAIN RAIN IN PARTS OF SOUTHERN AND CENTRAL NY AND
SOUTHERN NEW ENGLAND.


...PACIFIC NORTHWEST/CALIFORNIA/NORTHERN ROCKIES ...

A SLOW CYCLONIC CIRCULATION IS FORECAST TO DRIFT EAST SOUTHEAST
ACROSS THE NORTH PACIFIC THROUGH THE WEEKEND. GREATER COVERAGE AND
AMOUNTS OF SNOW RAMP UP SUNDAY AS COLDER AIR FILTERS IN BEHIND THE
STRONG PACIFIC COLD FRONT. THE LEFT EXIT REGION OF A MID-UPPER
LEVEL JET ROUNDING THE BASE OF THE CLOSED LOW IS EXPECTED TO
ENHANCE LIFT ACROSS THE INTERIOR NORTHWEST ALONG WITH INCREASING
UPPER DIFFLUENCE. HEAVY SNOW IS EXPECTED FOR THE HIGHER ELEVATIONS
OF SRN OR INTO NRN CA AS WELL AS THE SIERRA NEVADA RANGE...WITH A
MULTI-DAY TOTAL OF A FOOT POSSIBLE.


...DAY 3 MON...

...PACIFIC NORTHWEST/CALIFORNIA/NORTHERN ROCKIES AND GREAT BASIN...

THE MODELS ARE CLUSTERED ON THE 700 MB LOW CENTERED OVER WA STATE
BY 12Z MON...WHICH MOVES SLOWLY NORTHEAST TOWARDS THE BC/ALBERTA
BORDER...WITH THE TRAILING FRONT MOVING EAST ACROSS WESTERN
MT/ID/EASTERN NV/UT/WY. SEVERAL ADDITIONAL INCHES OF SNOW ARE
POSSIBLE IN THE WA/OR CASCADES IN THE POST FRONTAL ENVIRONMENT AS
STEEP LAPSE RATES ARE IN PLACE 850-700 MB WITH NEAR 7 DEG C/KM
PLUS DEEP MOISTURE WITH LAYER RH 90-99 PERCENT EARLY IN THE
PERIOD. LOW LEVEL WESTERLY FLOW DEVELOPS WITH WINDWARD TERRAIN
ACTING T PROVIDE LIFT...WITH A RESPONSE AIDED BY THE FAVORABLE
LAPSE RATES.

FURTHER INLAND IN THE RANGES OF ID/MT/NORTHWEST WY/UT THE FALLING
HEIGHTS AND FRONTAL CONVERGENCE LEAD TO A PERIOD OF SNOW WITH
ACCUMULATIONS FOCUSED ON HIGHER ELEVATIONS
SLIGHT TIMING DIFFERENCES LEAD TO DIFFERENCES CONCERNING HOW FAR
EAST ACROSS MT THE THREAT OF ACCUMULATING SNOW EXTENDS. THE UPPER
TROUGH MOVING ONSHORE AND INLAND IN CA LEADS TO DRYING ALOFT AND
DYING ASCENT...BRINGING THE EVENT TO A CLOSE THERE.


...NEW ENGLAND...
AS THE TRIPLE POINT CYCLOGENESIS OCCURS OVER THE MID ATLANTIC
STATES AND THE HIGH DEPARTS THROUGH THE CANADIAN
MARITIMES...STRONG LOW-MID LEVEL WARM ADVECTION CONTINUES ACROSS
INTERIOR NEW ENGLAND. THE IN PLACE COLD AIR GETS ERODED OVER
TIME...WITH A PERIOD OF ICE PELLETS AND FREEZING RAIN OVER
INTERIOR MAINE AND NORTHERN NH/VT/NY BEFORE THE TRANSITION BACK TO
RAIN. THE UNCERTAINTY CONTINUES TO BE THE EXPECTATION OF MULTIPLE
PRECIP TYPES AND THE DURATION OF EACH TYPE.

PETERSEN


$$




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FOUS11 KWBC 141947
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EDT SAT APR 14 2018

VALID 00Z SUN APR 15 2018 - 00Z WED APR 18 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND CALIFORNIA TO THE NORTHERN ROCKIES...

SNOW WILL BECOME INCREASINGLY WIDESPREAD FROM THE PACIFIC
NORTHWEST AND CALIFORNIA TO THE NORTHERN ROCKIES LATE THIS WEEKEND
AND INTO EARLY NEXT WEEK AS HEIGHTS AND SNOW LEVELS LOWER WITH AN
UPPER TROUGH MOVING INLAND OVER THE WESTERN U.S.. THERE IS STILL
SOME UNCERTAINTY WITH THE TIMING OF THE TROUGH, BUT THERE WAS A
DECENT CONSENSUS THAT THE GREATEST CHANCE FOR ACCUMULATIONS TO
EXCEED 8-INCHES WILL BE ALONG THE WASHINGTON CASCADES, SIERRA
NEVADA, SAWTOOTH MOUNTAINS, AND BITTERROOT RANGE, WHICH IS
SUPPORTED BY THE LATEST WPC PROBABILITIES.

SNOW COULD POTENTIALLY SPREAD OUT INTO THE NORTHERN HIGH PLAINS ON
TUESDAY AS THE UPPER TROUGH EJECTS EAST OF THE ROCKIES AND AN
INVERTED TROUGH AXIS EXTENDS NORTHWESTWARD FROM A SURFACE LOW
DEEPENING IN THE CENTRAL PLAINS. HOWEVER, THERE IS LIMITED
PREDICTABILITY WITH ACCUMULATIONS GIVEN THE UNCERTAINTY WITH THE
TIMING OF THE UPPER TROUGH. WPC PROBABILITIES CURRENTLY KEEP THE
DAY 3 SLIGHT RISK FOR ACCUMULATIONS TO EXCEED 4-INCHES CONFINED TO
EXTREME NORTHEASTERN MONTANA AND NORTHWESTERN NORTH DAKOTA.



...UPPER MISSISSIPPI VALLEY TO THE GREAT LAKES AND NORTHEAST...

A POWERFUL SPRING STORM WILL CONTINUE TO IMPACT THE EASTERN HALF
OF THE NATION OVER THE NEXT FEW DAYS AS A HIGHLY AMPLIFIED UPPER
TROUGH AND A SPRAWLING SURFACE SYSTEM EDGE EASTWARD OUT OF THE
MISSISSIPPI VALLEY ON SUNDAY, BEFORE PIVOTING NORTHEASTWARD
THROUGH THE GREAT LAKES AND NEW ENGLAND ON MONDAY.

MODERATE TO HEAVY SNOW IS EXPECTED WITHIN THE DEFORMATION
AXIS/COMMA HEAD, WHICH SHOULD ALIGN OVER THE UPPER MISSISSIPPI
VALLEY SATURDAY NIGHT INTO SUNDAY. DETERMINISTIC GUIDANCE IS
SHOWING SOME SPREAD WITH THE RESULTING SWATH OF ACCUMULATING SNOW,
BUT WPC PROBABILISTIC GUIDANCE IS SHOWING AT LEAST A MODERATE RISK
OF GREATER THAN 8-INCH SNOWFALL ACCUMULATIONS ACROSS MUCH OF
WISCONSIN AND THE U.P. OF MICHIGAN AND A NARROW MODERATE RISK OF
SNOWFALL ACCUMULATIONS IN EXCESS OF A FOOT EXTENDING FROM NORTHERN
WISCONSIN INTO WESTERN PORTIONS OF THE U.P..

FARTHER EAST, A MESSY MIX OF SNOW, SLEET, AND FREEZING RAIN IS
EXPECTED WITHIN PRECIPITATION DEVELOPING TO THE NORTH OF A STRONG
SURFACE FRONT STRETCHED THROUGH THE OHIO VALLEY AND NORTHERN
MID-ATLANTIC STATES SATURDAY NIGHT INTO SUNDAY. THERE REMAINS
PLENTY OF UNCERTAINTY WITH THE FORECAST AND IMPORTANT DETAILS OF
THERMAL PROFILES AND COLD AIR DAMMING IN THE NORTHEAST, BUT THE
LATEST MODEL GUIDANCE STILL SUGGESTS A STRONG SURFACE HIGH
CENTERED NEAR JAMES BAY IN CANADA WILL PROVIDE ENOUGH LOW LEVEL
COLD AIR TO ALLOW FOR RARE MID-APRIL FREEZING RAIN/ACCUMULATING
ICE. THE WINTRY MIX OF PRECIPITATION, AND THREAT FOR ACCUMULATING
ICE, SHOULD GRADUALLY SPREAD NORTHWARD THROUGH MAINE AS THE SYSTEM
BEGINS TO PIVOTS NORTHEASTWARD SUNDAY NIGHT INTO TUESDAY. WPC
PROBABILITIES CONTINUE TO SHOW A STRONG SIGNAL FOR ICE
ACCUMULATIONS TO EXCEED 0.25" ACROSS PORTIONS OF LOWER MICHIGAN
AND NEW YORK DURING THE DAY 1 PERIOD (00Z SUN - 00Z MON), BUT
AGAIN, GIVEN THE UNCERTAINTY, THE FORECAST SHOULD BE CLOSELY
MONITORED.


GERHARDT


$$




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FOUS11 KWBC 150810
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
409 AM EDT SUN APR 15 2018

VALID 12Z SUN APR 15 2018 - 12Z WED APR 18 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND CALIFORNIA TO THE NORTHERN ROCKIES...

SNOW WILL BECOME INCREASINGLY WIDESPREAD FROM THE PACIFIC
NORTHWEST AND CALIFORNIA TO THE NORTHERN ROCKIES SUN TO TUE AS
HEIGHTS AND SNOW LEVELS LOWER WITH AN UPPER TROUGH MOVING ONSHORE
AND THEN INLAND OVER THE WESTERN U.S.. THERE WAS A CONSENSUS THAT
THE GREATEST CHANCE FOR ACCUMULATIONS TO EXCEED 8-INCHES WILL BE
ALONG THE WASHINGTON-OR CASCADES, CA SIERRA NEVADA, SAWTOOTH
MOUNTAINS, AND BITTERROOT RANGE, WHICH IS SUPPORTED BY THE LATEST
WPC PROBABILITIES. THE GREATEST AMOUNTS ARE FORECAST TO BE 1-2
FEET OVER THE NORTHERN WA CASCADES AND CA SIERRA NEVADA MOUNTAINS.
MOST ACCUMULATIONS FALL SUN-MON WITH A BREAK COMING TUE AS THE
UPPER TROUGH MOVES EAST ON TO THE NORTHERN PLAINS AND AN UPPER
RIDGE APPROACHES AND CROSSES THE PACIFIC NORTHWEST.

THE NORTHWEST MT FRONT RANGE HAS A BETTER CHANCE OF RECEIVED
SEVERAL ADDITIONAL INCHES OF SNOW TUE. ALSO...ONCE THE UPPER
RIDGE PASSES YET ANOTHER UPPER TROUGH APPROACHES WA STATE FROM THE
EASTERN PACIFIC...SO SNOW MAY REDEVELOP IN ADVANCE OF THE UPPER
TROUGH AS THE GFS/ECMWF INDICATE DIFLUENT FLOW ALOFT WITH EMBEDDED
UPPER DIVERGENCE MAXIMA IN PLACE TO SUPPORT LIFT.


...CENTRAL AND NORTHERN PLAINS TUE...

THE MODELS INDICATE A 700 MB WAVE AND ASSOCIATED FRONT TO MOVE
EAST ACROSS WY AND CO TUE WITH SURFACE LOW PRESSURE DEVELOPING AND
MOVING ACROSS KS TO NEAR THE KS/NE BORDER BY 12Z TUE. NORTH OF
THE LOW...MID LEVEL FRONTOGENESIS AND DEFORMATION DEVELOPS ALONG
WITH 700 MB CONVERGENCE...SO PRECIP BREAKS OUT ON THE CENTRAL
PLAINS AS THE WAVE APPROACHES. INITIAL TEMPS AHEAD OF THE WAVE
ARE TOO WARM FOR SNOW...WITH FALLING HEIGHTS/TEMPS ALOFT CHANGING
RAIN OVER TO SNOW. SEVERAL INCHES OF SNOW IS POSSIBLE OVER
PORTIONS OF SOUTHEAST SD TO ADJACENT NORTHEAST NEBRASKA. THE
UNCERTAINTY RELATES TO THE WAVE TIMING/SFC LOW DEVELOPMENT...WITH
THE GFS/CANADIAN FASTER IN MOVING THE WAVE EAST THAN THE PREFERRED
ECMWF/UKMET. THE 00Z NAM HAD SIMILAR TIMING WITH A LOW TRACK
FURTHER SOUTH. LIGHT SNOWS ARE POSSIBLE AHEAD OF THE ASSOCIATED
LOW LEVEL FRONT IN THE NORTHERN PLAINS AS WELL.


...UPPER MISSISSIPPI VALLEY TO THE GREAT LAKES AND NORTHEAST...

HEAVY SNOW IS EXPECTED WITHIN THE DEFORMATION AXIS OVER NORTHERN
WI INTO THE UP OF MI...WHERE A LAKE ENHANCEMENT FROM LONG CROSS
LAKE TRAJECTORIES ON NORTHEAST WINDS ADDS TO THE QPF AND RESULTANT
SNOW. 12-18 INCHES IS EXPECTED OVER THE UP OF MI. ON SUN-SUN
NIGHT...SUPPORTED BY THE GLOBAL MODELS CONSENSUS AND THE HIGH RES
ENSEMBLES MEMBERS SHOWING AS MUCH AS 2 INCHES LIQUID EQUIVALENT
JUST OFF LK SUPERIOR IN THE CENTRAL UP OF MI. WITH THE MODELS
STILL SHOWING MID LEVEL WARMING ABOVE FREEZING...AND AREA OF ICE
PELLETS IS EXPECTED IN NORTHERN LOWER MI...GRADUALLY TRANSITIONING
TO FREEZING RAIN OVER CENTRAL LOWER MI...WHERE MULTIPLE MODELS
STILL INDICATE POTENTIAL FOR QUARTER TO HALF INCH LIQUID
EQUIVALENT INT HE FORM OF FREEZING RAIN ON EXPOSED SURFACES.

A FEW MORE INCHES OF SNOW IS POSSIBLE MONDAY MORNING BEFORE THE
LOW DEPARTS INTO CANADA AND THE PRECIPITATION COVERAGE/INTENSITY
TAPERS.

FARTHER EAST, A MESSY MIX OF SLEET AND FREEZING RAIN IS EXPECTED
WITHIN PRECIPITATION DEVELOPING TO THE NORTH OF A STRONG SURFACE
FRONT STRETCHED THROUGH THE OHIO VALLEY AND NORTHERN MID-ATLANTIC
STATES SUNDAY. THERE REMAINS PLENTY OF UNCERTAINTY WITH THE
FORECAST AND IMPORTANT DETAILS OF THERMAL PROFILES AND COLD AIR
DAMMING IN THE NORTHEAST
THE LATEST MODEL GUIDANCE STILL SUGGESTS A STRONG SURFACE HIGH
CENTERED NEAR JAMES BAY IN CANADA WILL PROVIDE ENOUGH LOW LEVEL
COLD AIR TO ALLOW FOR FREEZING RAIN/ACCUMULATING ICE CENTERED ON
TERRAIN OF EASTERN NY AND VT/ADJACENT MA.

ON TUESDAY...WITH THE TRIPLE POINT LOW MOVING NORTH...THE WINTRY
MIX OF PRECIPITATION, AND THREAT FOR ACCUMULATING ICE, SHOULD
GRADUALLY SPREAD NORTHWARD THROUGH INTERIOR MAINE TUESDAY. THE
LOW DEPARTING NORTH OF THE BORDER ALTER TUE SIGNS THAT THE PRECIP
EVENT SHOULD BE WINDING DOWN.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT DAY 3
(TUE).

PETERSEN


$$




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FOUS11 KWBC 152115
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
514 PM EDT SUN APR 15 2018

VALID 00Z MON APR 16 2018 - 00Z THU APR 19 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND CALIFORNIA TO THE NORTHERN AND CENTRAL
ROCKIES...

WIDESPREAD SNOWFALL IS EXPECTED WITH AN UPPER TROUGH MOVING INLAND
OVER THE WESTERN U.S. SUNDAY NIGHT. MODEL GUIDANCE REMAINED IN
AGREEMENT THAT LOWERING HEIGHTS AND SNOW LEVELS WITH THE TROUGH
WILL SUPPORT PERIODS OF MODERATE TO HEAVY SNOW ALONG THE CASCADES,
SIERRA NEVADA, AND SAWTOOTH RANGE SUNDAY NIGHT INTO MONDAY, WITH
ACTIVITY SHIFTING INTO THE NORTHERN/CENTRAL ROCKIES MONDAY NIGHT
INTO TUESDAY AS THE ASSOCIATED COLD FRONT PROGRESSES EASTWARD OUT
OF THE GREAT BASIN. THE RISK FOR ANY WIDESPREAD SNOWFALL
ACCUMULATIONS TO EXCEED A FOOT SHOULD BE LIMITED TO THE WASHINGTON
CASCADES AND SIERRA NEVADA DURING THE DAY 1 PERIOD (VALID 00Z SUN
- 00Z MON).


...CENTRAL AND NORTHERN PLAINS TO THE UPPER MISSISSIPPI VALLEY...

ANOTHER ROUND OF LATE SEASON SNOWFALL WILL BE POSSIBLE OVER
PORTIONS OF THE CENTRAL/NORTHERN PLAINS AND UPPER MISSISSIPPI
VALLEY TUESDAY NIGHT INTO WEDNESDAY AS A VIGOROUS UPPER TROUGH
EJECTS OUT OF THE ROCKIES AND CLOSES OFF OVER NEBRASKA/IOWA. SNOW
WILL BE POSSIBLE WITHIN AN AXIS OF MOISTURE AND CONVERGENCE
ALIGNING OVER NORTH AND SOUTH DAKOTA, BUT THE GREATEST CHANCE FOR
SNOW (AND HIGHEST ACCUMULATIONS) SHOULD BE WITHIN A DEFORMATION
ZONE SETTING UP TO NORTH/NORTHWEST OF A RAPIDLY DEEPENING SURFACE
CYCLONE. THERE CONTINUES TO BE A FAIR AMOUNT OF MODEL SPREAD WITH
THE TIMING AND WHOLE EVOLUTION OF THE MID-LEVEL ENERGY, WHICH IS
CURRENTLY LIMITING THE PREDICTABILITY OF THE DETAILS OF THE
FORECAST. HOWEVER, WPC PROBABILITIES ARE ALREADY ADVERTISING AT
LEAST A SLIGHT RISK FOR SNOWFALL ACCUMULATIONS TO EXCEED 8-INCHES
WITH THIS EVENT.


...GREAT LAKES AND NORTHEAST...

A POWERFUL SPRING STORM WILL CONTINUE TO IMPACT LOCATIONS ACROSS
THE GREAT LAKES AND NORTHEAST SUNDAY NIGHT INTO MONDAY AS A HIGHLY
AMPLIFIED UPPER TROUGH AND AN OCCLUDED COLD FRONT GRADUALLY PIVOT
NORTHEASTWARD THROUGH THE REGION. MODERATE TO HEAVY SNOW WITHIN
THE DEFORMATION ZONE LIFTING THROUGH THE UPPER GREAT LAKES SHOULD
RESULT IN AT LEAST AN ADDITIONAL 4-INCHES ACROSS THE MINNESOTA
ARROWHEAD, U.P., AND NORTHERN LOWER MICHIGAN, WHICH IS HIGHLIGHTED
BY THE MODERATE RISK OF SNOWFALL ACCUMULATIONS TO EXCEED 4-INCHES
IN THE LATEST DAY 1 WPC PROBABILITIES (VALID 00Z MON-00Z TUE).

FARTHER EAST, A MESSY MIX OF SLEET AND FREEZING RAIN IS EXPECTED
WITHIN THE NORTHERN EDGE OF PRECIPITATION SPREADING NORTHWARD
THROUGH THE NORTHEAST SUNDAY NIGHT INTO MONDAY. DESPITE A MELTING
LAYER ALOFT, MODEL GUIDANCE IS IN AGREEMENT THAT COLD AIR IN THE
LOWER LEVELS SHOULD REMAIN WEDGED IN LONG ENOUGH TO ALLOW FOR
ACCUMULATING ICE OVER MUCH OF INTERIOR NEW ENGLAND. WPC
PROBABILITIES SUGGEST THAT THERE IS AT LEAST A SLIGHT RISK FOR ICE ACCUMULATIONS TO EXCEED 0.25" ACROSS THE REGION.

THE THREAT FOR SNOW AND ICE WITH THIS STORM SHOULD FINALLY COME TO
AN END LATE MONDAY/EARLY TUESDAY AS THE BEST MOISTURE AND FORCING
LIFT INTO CANADA. HOWEVER, BROAD CYCLONIC FLOW ALOFT SHOULD HELP
FOSTER SNOW SHOWERS DOWNWIND OF THE LAKES AND ALONG PORTIONS THE
APPALACHIANS THROUGH TUESDAY.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT DAY 3
(TUE).

GERHARDT


$$




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FOUS11 KWBC 160819
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
419 AM EDT MON APR 16 2018

VALID 12Z MON APR 16 2018 - 12Z THU APR 19 2018


DAYS 1-3...

...PACIFIC NORTHWEST AND CALIFORNIA TO THE NORTHERN AND CENTRAL
ROCKIES...

WIDESPREAD SNOWFALL IS EXPECTED WITH AN UPPER TROUGH MOVING INLAND
OVER THE NORTHWESTERN U.S. MODEL GUIDANCE REMAINED IN AGREEMENT
THAT LOWERING HEIGHTS AND SNOW LEVELS WITH THE TROUGH WILL SUPPORT
PERIODS OF MODERATE TO HEAVY SNOW ALONG THE WA-OR CASCADES, SIERRA
NEVADA, AND SAWTOOTH RANGE TODAY, WITH ACTIVITY INTO THE
NORTHERN/CENTRAL ROCKIES MONDAY NIGHT INTO TUESDAY AS THE
ASSOCIATED COLD FRONT PROGRESSES EASTWARD OUT OF THE GREAT BASIN
AND UPPER DIVERGENCE MAXIMA MOVING NORTH ACROSS ID AND WESTERN MT.
THE HEAVIEST SNOW IS FORECAST TO BE 1- FEET OVER THE WASHINGTON
CASCADES.
SEVERAL INCHES ARE EXPECTED ON TUE IN THE RANGES OF WY AS THE AREA
EXPERIENCES PRE-FRONTAL CONVERGENCE AS THE 700 MB FRONT APPROACHES
AND THEN ARRIVES. A BREAK COMES WED AS THE UPPER TROUGH MOVES EAST
ON TO THE PLAINS.

SNOWS MAY REDEVELOP AS THE NEXT UPPER TROUGH FROM THE EASTERN
PACIFIC APPROACHES WESTERN OR AND CA. THERE IS A SPREAD IN TROUGH TIMING/AMPLITUDE AND THUS PRECIP AND SNOW AMOUNTS TO BE RESOLVED
LATER. CONSEQUENTLY A LOW RISK OF HEAVY SNOW IS INDICATED IN THE PROBABILITIES.

...CENTRAL AND NORTHERN PLAINS TO THE UPPER MISSISSIPPI VALLEY...

AN AREA OF SNOWFALL WILL BE POSSIBLE OVER PORTIONS OF THE
CENTRAL/NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY TUESDAY NIGHT
INTO WEDNESDAY AS A VIGOROUS UPPER TROUGH EJECTS OUT OF THE
ROCKIES AND A CLOSED OFF MOVES FROM KANSAS TO NEAR THE
NEBRASKA/IOWA/MISSOURI BORDER INTO IOWA. SNOW WILL BE POSSIBLE
WITHIN AN AXIS OF MOISTURE AND CONVERGENCE ALIGNING WITHIN A
DEFORMATION ZONE SETTING UP TO NORTH/NORTHWEST OF THE DEEPENING
SURFACE CYCLONE. THERE CONTINUES TO BE A FAIR AMOUNT OF MODEL
SPREAD WITH THE TIMING AND EVOLUTION OF THE SYSTEM, WHICH IS
IMPACTING BOTH THE AXIS/ORIENTATION AND POTENTIAL AMOUNTS.
GREATER WEIGHTING WAS GIVEN TO THE NAM/UKMET/ECMWF AND ECMWF
ENSEMBLE MEAN SOLUTIONS...WITH THE GFS SHOWING FASTER MOVEMENT AND
MORE NORTHERN AXIS OF THE FORECAST SNOWFALL. THE PREFERRED
CLUSTER PROVIDES POTENTIAL FOR 6-10 INCHES OF SNOW.

...UPPER GREAT LAKES...

THE AREA OF HEAVY SNOW OCCURRING IN AREAS ADJACENT TO LAKE
SUPERIOR IS EXPECTED TO PERSIST MONDAY INTO MONDAY NIGHT INTO
MONDAY AS THE LOW LEVEL CYCLONE DRIFTS SLOWLY
NORTHEAST....ALLOWING AN EXTENDED PERIOD OF LEE AREA CONVERGENCE
TO OCCUR IN THE UP OF MI.
SEVERAL ADDITIONAL INCHES OF SNOW IS EXPECTED TODAY BEFORE
TAPERING TONIGHT AS THE LOW MOVES ACROSS THE BORDER INTO CANADA.
AS THE LOW DEPARTS...NORTHWEST FLOW DEVELOPS IN THE UP OF MI
ACROSS NORTHERN LAKE MICHIGAN....WITH ENHANCED MOISTURE AND LEE
SHORE CONVERGENCE RESULTING IN SEVERAL INCHES OF SNOW IN NORTHWEST
LOWER MICHIGAN.

...NORTHEAST...

A MESSY MIX OF SLEET AND FREEZING RAIN IS EXPECTED WITHIN THE
NORTHERN EDGE OF PRECIPITATION SPREADING NORTHWARD THROUGH MONDAY
ACROSS NORTHERN NEW YORK AND NORTHERN NEW ENGLAND. DESPITE A
MELTING LAYER ALOFT, MODEL GUIDANCE IS IN AGREEMENT THAT COLD AIR
IN THE LOWER LEVELS SHOULD REMAIN DAMMED IN LONG ENOUGH TO ALLOW
FOR ACCUMULATING ICE OVER MUCH OF INTERIOR NORTHERN NEW ENGLAND.
WPC PROBABILITIES SUGGEST THAT THERE IS A SLIGHT TO MODERATE RISK
FOR ICE ACCUMULATIONS TO EXCEED 0.25" ACROSS INTERIOR MAINE AND NH.

THE THREAT FOR SNOW AND ICE WITH THIS STORM SHOULD FINALLY COME TO
AN END LATE MONDAY/EARLY TUESDAY AS THE GREATEST MOISTURE AND
FORCING LIFT INTO CANADA. HOWEVER, BROAD CYCLONIC FLOW ALOFT
SHOULD HELP SUPPORT SNOW SHOWERS DOWNWIND OF THE LAKES INTO THE
CENTRAL APPALACHIANS.
THROUGH TUESDAY.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT DAY 2
(TUE) and 3 (WED).

PETERSEN


$$




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FOUS11 KWBC 162103
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
503 PM EDT MON APR 16 2018

VALID 00Z TUE APR 17 2018 - 00Z FRI APR 20 2018


DAYS 1-3...

...GREAT LAKES/NORTHEAST...

A BROAD UPPER LOW...RESPONSIBLE FOR THE WIDESPREAD MODERATE TO
HEAVY PRECIPITATION ACROSS THE CENTRAL-EASTERN U.S. THE PAST FEW
DAYS IS EXPECTED TO GRADUALLY LIFT NORTHEAST ACROSS THE
NORTHEASTERN U.S. MON NIGHT AND TUE. COLD AIR WRAPPING AROUND THE
BACKSIDE OF A CONSOLIDATING SURFACE LOW OVER SOUTHEASTERN CANADA
WILL SUPPORT RAIN CHANGING TO SNOW...WITH GUIDANCE SHOWING THE
POTENTIAL FOR SOME LOCALLY HEAVY ACCUMULATIONS...PARTICULARLY
ACROSS PORTIONS OF THE WESTERN U.P. OF MI...NORTHWEST PA AND
UPSTATE NY...WHERE OROGRAPHIC LIFT/LAKE-ENHANCEMENT MAY HELP TO
BOLSTER AMOUNTS. WPC DAY 1 PROBABILITIES (ENDING 00 UTC WED) SHOW
AT LEAST A SLIGHT RISK FOR ACCUMULATIONS OF 4-INCHES OR MORE
ACROSS THESE AREAS. AHEAD OF THE LOW...ACCUMULATING FREEZING RAIN
IS POSSIBLE...WITH DAY 1 PROBABILITIES SHOWING A SLIGHT RISK FOR
ACCUMULATIONS OF 0.25 INCH OR MORE ACROSS PORTIONS OF NORTHERN
MAINE.

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A DEEP UPPER TROUGH IS FORECAST TO MOVE ACROSS THE WESTERN U.S.
MON NIGHT AND TUE...WITH LOCALLY HEAVY MOUNTAIN SNOWS POSSIBLE IN
THE WAKE OF A WELL-DEFINED COLD FRONT TRAVERSING THE REGION.
HEAVIEST ACCUMULATIONS ARE EXPECTED TO FALL ALONG THE NORTHERN CASCADES...NORTHERN IDAHO...WESTERN MONTANA AND NORTHWESTERN
WYOMING RANGES...WITH WPC DAY 1 PROBABILITIES SHOWING THE
POTENTIAL FOR 8-INCHES OR MORE ACROSS SOME OF THE HIGHER TERRAIN.

INITIAL TROUGH IS FORECAST TO MOVE PROGRESSIVELY INTO THE CENTRAL
U.S. TUE NIGHT. HOWEVER...PRECIPITATION IS EXPECTED TO RETURN TO
PORTIONS OF THE WEST BY LATE WED AS A CLOSED LOW DROPS SOUTHEAST
INTO NORTHERN CA. WITH LIMITED MOISTURE...WIDESPREAD HEAVY SNOW
TOTALS ARE NOT EXPECTED...HOWEVER GUIDANCE DOES SHOW THE POTENTIAL
FOR SOME LOCALLY HEAVY TOTALS...WITH WPC DAY 3 PROBABILITIES
(ENDING 00 UTC FRI) SHOWING AT LEAST A SLIGHT RISK FOR
ACCUMULATIONS OF 4-INCHES OR MORE ACROSS CENTRAL INTO NORTHEAST NV.

...NORTHERN PLAINS AND UPPER MIDWEST...

THE LEADING TROUGH TRAVERSING THE WESTERN U.S. ON DAY 1 IS
EXPECTED TO ASSUME A NEGATIVE-TILT AS IT MOVES INTO THE CENTRAL
U.S....WITH AN UPPER LOW CLOSING OFF OVER THE DAKOTAS TUE NIGHT.
IN ADDITION TO THE STRONG UPPER FORCING...LOW TO MID LEVEL
CONVERGENCE AND BAROCLINICITY ALONG A TROUGH EXTENDING NORTHWEST
OF THE ASSOCIATED SURFACE CYCLONE LIFTING NORTHEAST INTO THE MID
MS VALLEY IS EXPECTED TO SUPPORT A BROADENING AREA OF MODERATE
PRECIPITATION ACROSS THE DAKOTAS INTO SOUTHERN MN AND IA TUE
NIGHT. COLD AIR DRAWN SOUTH BY THE AMPLIFYING CYCLONE IS EXPECTED
TO SUPPORT RAIN CHANGING TO SNOW ACROSS EASTERN SD AND ALONG THE
MN/IA BORDER INTO SOUTHERN WI TUE NIGHT INTO EARLY WED. LOCALLY
HEAVY SNOW ACCUMULATIONS ARE POSSIBLE...WITH WPC DAY 2
PROBABILITIES (ENDING 00 UTC THU) SHOWING A MODERATE RISK FOR
ACCUMULATIONS OF 4-INCHES OR MORE AND A SLIGHT RISK FOR 8-INCHES
OR GREATER ACROSS THE REGION.

PEREIRA



$$




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FOUS11 KWBC 170728
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 AM EDT TUE APR 17 2018

VALID 12Z TUE APR 17 2018 - 12Z FRI APR 20 2018


DAYS 1-3...

...PACIFIC NORTHWEST/NORTHERN TO CENTRAL ROCKIES/GREAT BASIN...

COVERAGE AND INTENSITY OF SNOW IS LIMITED ON DAY 1 AS THE UPPER
TROUGH DEAMPLIFIES OVER THE NORTHWEST US AND A MID-UPPER RIDGE
APPROACHES FROM THE EASTERN PACIFIC. SEVERAL INCHES OF SNOW ARE
POSSIBLE IN THE WA CASCADES TUE AS DEEP WESTERLY FLOW AND HIGH
LAYER RELATIVE HUMIDITY INITIALLY NEAR 90 PERCENT GET LIFTED IN
WINDWARD TERRAIN WITH SNOW SHOWERS FOCUSED ON THE EARLY PART OF
TUE BEFORE DRIER AIR ALOFT MOVES INTO THE REGION. FURTHER
INLAND...
MOUNTAIN SNOWS POSSIBLE IN THE WAKE OF A WELL-DEFINED COLD FRONT
MOVING EAST OUT OF THE ROCKIES ON TO THE NORTHERN PLAINS. SEVERAL
INCHES ARE POSSIBLE IN THE
RANGES OF NORTHERN IDAHO...WESTERN MONTANA AND NORTHWESTERN
WYOMING RANGES...WITH WPC DAY 1 PROBABILITIES SHOWING THE
POTENTIAL FOR 8-INCHES OR MORE ACROSS SOME OF THE HIGHER TERRAIN.

LIGHT SNOW DEVELOPS IN THE RANGES OF SOUTHWEST OR AND NORTHWEST CA
ON WED AS THE NEXT EASTERN PACIFIC TROUGH MOVES EAST SOUTHEAST AND
PRODUCES COUPLED LOW-MID LEVEL CONVERGENCE AND UPPER DIVERGENCE
WED NIGHT AS THE TROUGH COMES ONSHORE.
WITH LIMITED MOISTURE...WIDESPREAD HEAVY SNOW TOTALS ARE NOT
EXPECTED.

ON DAY 3 LOW LEVEL CONVERGENCE IN THE VICINITY OF THE 700 MB LOW
AS IT CROSSES NV LEADS TO DEVELOPMENT OF HIGHER ELEVATION
SNOWS....WITH WPC DAY 3 PROBABILITIES SHOWING AT LEAST A SLIGHT
RISK FOR ACCUMULATIONS OF 4-INCHES OR MORE ACROSS CENTRAL INTO
NORTHEAST NV.
AS THE LOW MOVES EAST TOWARDS UT...MOIST SOUTHERLY DEEP LAYERED
FLOW DEVELOPS ACROSS THE RANGES OF SOUTHWEST CO...WITH LIFT
ACCOMPANYING THE WARM/MOISTURE ADVECTION IN TO THE SAN JUAN MNTNS.
SEVERAL INCHES ARE POSSIBLE FOLLOWING AN EARLY DRY PERIOD A
SUSTAINED MOISTURE AND LIFT PERSISTS LATE THU NIGHT TO FRI MORNING.

...NORTHERN TO CENTRAL PLAINS AND UPPER MIDWEST...

A MID-UPPER TROUGH ON DAY 1 IS EXPECTED TO ASSUME A NEGATIVE-TILT
AS IT MOVES INTO THE CENTRAL U.S....WITH A 700 MB LOW CLOSING OFF
OVER SOUTH DAKOTA TO SOMEWHERE EITHER IN IOWA OR MN WED BEFORE
MERGING WITH THE NORTHERN STREAM WAVE AS IT CROSSES THE UPPER
GREAT LAKES ON WED NIGHT-EARLY THU. IN ADDITION TO THE STRONG
UPPER FORCING...LOW TO MID LEVEL CONVERGENCE AND FRONTOGENESIS
ALONG A TROUGH EXTENDING NORTHWEST OF THE ASSOCIATED SURFACE
CYCLONE LIFTING NORTHEAST INTO THE MID MS VALLEY IS EXPECTED TO
SUPPORT A BROADENING AREA OF PRECIPITATION ACROSS SOUTH DAKOTA
INTO SOUTHERN MN AND NORTHERN IA TUE NIGHT INTO WI AND IL WED.
LIGHT AMOUNTS ARE ALSO EXPECTED IN ADVANCE OF THE FRONT IN NORTH
DAKOTA ON TUE.

COLD AIR ADVECTED SOUTH BY THE AMPLIFYING CYCLONE IS EXPECTED TO
SUPPORT RAIN CHANGING TO SNOW ACROSS EASTERN SD AND POSSIBLY
ADJACENT NORTHEAST NE TO NORTHERN IOWA/SOUTHERN MN...CONTINUING
INTO WI WED. LOCALLY HEAVY SNOW ACCUMULATIONS ARE POSSIBLE...AS
THE 00Z NAM SHOWS COMBINED STRONG 700 MB CONVERGENCE AND THETA-E
ADVECTION IN NORTHERN IA TO ADJACENT SOUTHERN MN WITH WPC DAY 2
PROBABILITIES SHOWING A MODERATE RISK FOR ACCUMULATIONS OF 8
INCHES OR MORE IN THESE AREAS.


...GREAT LAKES/NORTHEAST...

COLD AIR WRAPPING AROUND THE BACKSIDE OF A SURFACE LOW OVER
SOUTHEASTERN CANADA WILL SUPPORT SNOW...WITH GUIDANCE SHOWING THE
POTENTIAL FOR SOME LOCALLY HEAVY ACCUMULATIONS ACROSS PORTIONS OF
THE TUG HILL PLATEAU OF NY...WHERE OROGRAPHIC LIFT AND LAKE
ENHANCEMENT SHOULD HELP TO ENHANCE AMOUNTS ON TUE. LAKE ENHANCED
SNOW ALSO IS EXPECTED DOWNWIND FROM LAKE ERIE TO NORTHWEST PA TO
ADJACENT OH/FAR SOUTHWEST NY.
AS THE LOW IN CANADA MOVES FURTHER EAST...THE SNOW ON DAY 2 IS
FORECAST TO BE LIGHT AND PRIMARY IN WINDWARD TERRAIN OF THE
NORTHERN GREEN MNTNS OF VT AND ACROSS PORTIONS OF WESTERN MAINE.

ON DAY 3...THE MODELS SHOW THE DEVELOPMENT OF A TRIPLE POINT LOW
IN NEW YORK AND NEW ENGLAND...CONTINUING INTO THE GULF OF MAINE.
NORTH OF THE LOW...SNOW IS EXPECTED ACROSS NORTHERN NEW YORK AND
NORTHERN NEW ENGLAND. IF THE LOW IS A BIT STRONGER LIKE THE GFS
AND/OR 00Z ECMWF...THERE IS POTENTIAL FOR SEVERAL INCHES IN
NORTHERN NEW ENGLAND.
LOW LEVEL COLD ADVECTION ACROSS THE LAKES WITH ENHANCED MOISTURE
FLUXES IS EXPECTED TO PRODUCE LAKE ENHANCEMENTS OFF LK ONTARIO
INTO AREAS DOWNSTREAM ALONG THE SOUTHEAST SHORE LINE OF LK ONTARIO
AND LK ERIE THU NIGHT.

THE PROBABILITY OF FREEZING RAIN GREATER THAN 0.25 INCHES IS LESS
THAN 10 PERCENT DAYS 1-3.

PETERSEN



$$




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FOUS11 KWBC 172014
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
413 PM EDT TUE APR 17 2018

VALID 00Z WED APR 18 2018 - 00Z SAT APR 21 2018


DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES...

SNOW WILL RETURN TO PARTS OF THE WESTERN TERRAIN ON THURS AND FRI,
WITH THE RETURN OF A POTENT SHORT WAVE TROUGH ARRIVING FROM THE
PAC. THE GLOBAL MODELS AND ENSEMBLES CAPTURE THIS FEATURE ARRIVING
INTO CENTRAL CA TOWARD THE DESERT SOUTHWEST. EXPECT A FEW INCHES
OF ELEVATED SNOWFALL A FOR THE CENTRAL TO SOUTHERN SIERRA INTO NV.
THEN ON THURS, A LARGE CLOSED 500 MB CIRCULATION WILL SPREAD
DOWNSTREAM THROUGH TH FOUR CORNERS REGION WILL YIELD SOME
DYNAMICALLY DRIVEN AND UPSLOPE SNOWFALL FROM THE SOUTHERN WASATCH
INTO THE CO ROCKIES, ESPECIALLY FOR THE SAN JUANS INTO THE SANGRE
DE CHRISTO RANGE. WPC STAYED CLOSER TO THE SLOWER ECMWF THAN THE
FASTER GFS.


...NORTHERN/CENTRAL PLAINS AND UPPER/MID MS VALLEY INTO GREAT
LAKES AND NEW ENGLAND...

A DYNAMIC SHORT WAVE TROUGH, PUSHING THROUGH WY/CO THIS AFTERNOON,
WILL EJECT OUT ACROSS THE UPPER PLAINS AND PROCEED DOWNSTREAM
THROUGH THE UPPER/MID MS VALLEY TO LAKE MICHIGAN ON WED. A CLOSED
MID TO UPPER LOW ACCOMPANYING THIS COMPACT SYSTEM WILL YIELD A
SWATH OF HEAVY SNOWFALL FROM NERN NE THROUGH NORTHERN IA INTO
SOUTHERN WI. MUCH OF THIS SNOW WILL BE RATHER INTENSE WITH HIGH
RATES, AS STRONG DYNAMIC COOLING TAKES PLACE WITHIN THE NWRN
PORTION OF THE LOW PRESSURE SYSTEM. THE GUIDANCE CAPTURES THIS
OVERALL SCENARIO WITH MINOR DETAIL SPREAD WITH THE HEAVIEST
SNOWFALL TOTALS ACROSS EXTREME NERN NE THROUGH NORTHERN IA.

THEN ON THURS AND FRI, THE MAIN SHORT WAVE TROUGH WILL BEGIN TO
INTERACT WITH A DIGGING NORTHERN STREAM JET. THE PARENT LOW
STREAKING ACROSS THE GREAT LAKES WILL WEAKEN, WHILE A TRIPLE POINT
JUST OFFSHORE OF SOUTHERN NEW ENGLAND DEEPENS AND LIFTS INTO THE
CANADIAN MARITIMES. THIS SHOULD YIELD OVERALL LIGHTER SNOWFALL
AMOUNTS ACROSS PARTS OF THE GREAT LAKES AND NEW ENGLAND.

THE PROBABILITY OF FREEZING RAIN GREATER THAN 0.25 INCHES IS LESS
THAN 10 PERCENT DAYS 1-3.

MUSHER



$$




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------------=_1524039816-17653-5740
Content-Type: text/plain

FOUS11 KWBC 180823
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
423 AM EDT WED APR 18 2018

VALID 12Z WED APR 18 2018 - 12Z SAT APR 21 2018


DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES/HIGH
PLAINS...

SNOW WILL RETURN AS AN EASTERN PACIFIC TROUGH AND JET APPROACHES
LATE WED WITH MOISTURE FLUXES AND LIFT PRODUCING LIGHT SNOWS IN
THE OR CASCADES.
ONCE THE UPPER TROUGH MOVES ONSHORE AN INLAND...EXPECT LIGHT
ELEVATED SNOWFALL FOR THE CENTRAL TO SOUTHERN CA SIERRA NEVADA
ACROSS THE RANGES OF CENTRAL NV. THEN ON THURS, A LARGE CLOSED 500
MB CIRCULATION WILL DRIFT DOWNSTREAM THROUGH THE FOUR CORNERS
REGION TO YIELD SOME DYNAMICALLY DRIVEN AND UPSLOPE SNOWFALL FROM
THE SOUTHERN WASATCH INTO THE CO ROCKIES, ESPECIALLY FOR THE SAN
JUANS INTO THE SANGRE DE CRISTO RANGE. SEVERAL MODELS/ENSEMBLE
MEANS INDICATE LOCALLY HEAVY SNOW IN THE SAN JUANS.

AS THE CIRCULATION DRIFTS EAST INTO THE HIGH PLAINS...LOW-MID
LEVEL CONVERGENCE MAXIMA AND PERSISTENT DEEP LAYERED HIGH RELATIVE
HUMIDITY FAVOR SNOW DEVELOPING FRI-FRI NIGHT IN THE FRONT
RANGE/PALMER RIDGE AND FOOTHILLS OF CENTRAL CO DOWN INTO THE
SANGRE DE CRISTO MOUNTAINS OF NM.

THE MODELS HAVE SLIGHT TEMPERATURE DIFFERENCES IN CO EAST OF THE
MOUNTAINS AND RESULTANT IMPACTS ON SNOW SAT. THE GFS HAS HIGHER
QPF TO ADJACENT WY AND THE NAM OVER IN NORTHEAST UT...WITH THE
RESPECTIVE MEANS GIVEN MORE WEIGHT UNTIL BETTER SUPPORT FOR THE
OPERATIONAL GFS AND NAM DEVELOPS WHERE THEY ARE OUTLIERS. THE
NAM/UKMET/212Z SREF MEAN ARE IN BETTER THAN AVERAGE AGREEMENT IN
PRODUCING SEVERAL INCHES OF SNOW ON FRI NIGHT-SAT IN THE RANGE OF
CO.


...UPPER/MID MS VALLEY ACROSS THE GREAT LAKES AND NEW YORK/NEW
ENGLAND...

A DYNAMIC SHORT WAVE TROUGH WILL PROCEED ACROSS THE UPPER/MID MS
VALLEY TO LAKE MICHIGAN ON WED. A CLOSED MID LEVEL LOW
ACCOMPANYING THIS COMPACT SYSTEM WILL YIELD A SWATH OF HEAVY
SNOWFALL ALONG A LOW LEVEL FRONTOGENESIS AND 700 MB CONVERGENCE
AXIS FROM NERN NE THROUGH NORTHERN IA INTO SOUTHERN WI. BANDS OF
1-2 INCHES PER HOURS ARE POSSIBLE TODAY IN NORTHERN IOWA. THE
GUIDANCE HAS NUDGED THE QPF AXIS A BIT SOUTH AGAIN TONIGHT...
ALTHOUGH AGREEMENT IS NOT AS MUCH AS WE USUALLY SEE ON A DAY 1
FORECAST. TIMING DIFFERENCES PERSIST AS THE CANADIAN GEM AND 12Z
ECMWF END SNOW SOONER IN EASTERN SD/EASTERN NE WHILE THE NAM/HIGH
RES WINDOWS ARE SLOWER AND HEAVIER.

ON THURS, THE MAIN SHORT WAVE TROUGH WILL BEGIN TO INTERACT WITH A
DIGGING NORTHERN STREAM JET. THE PARENT LOW STREAKING ACROSS THE
OHIO VALLEY/PA WILL WEAKEN, WHILE A TRIPLE POINT JUST OFFSHORE OF
SOUTHERN NEW ENGLAND DEEPENS AND LIFTS INTO THE CANADIAN
MARITIMES. THIS SHOULD YIELD OVERALL LIGHTER SNOWFALL AMOUNTS
ACROSS INTERIOR NEW YORK AND NEW ENGLAND. THE 00Z ECMWF TRENDED
FASTER IN MOVING THE LOW OFFSHORE, CUTTING BACK N QPF AND
POTENTIAL SNOW.

THE PROBABILITY OF FREEZING RAIN GREATER THAN 0.25 INCHES IS LESS
THAN 10 PERCENT DAYS 1-3.

PETERSEN



$$




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FOUS11 KWBC 182000
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
400 PM EDT WED APR 18 2018

VALID 00Z THU APR 19 2018 - 00Z SUN APR 22 2018


DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES...

SNOW WILL RETURN TO PARTS OF THE WESTERN TERRAIN THURS THROUGH
SAT, AS A POTENT SHORT WAVE TROUGH ARRIVES FROM THE PAC. THE
GLOBAL MODELS AND ENSEMBLES CAPTURE THIS FEATURE ARRIVING
INTO CENTRAL CA TOWARD THE DESERT SOUTHWEST ON THURS, THEN SLOWLY
PROGRESSING THROUGH THE FOUR CORNERS REGION INTO THE
CENTRAL/SOUTHERN PLAINS ON FRI/SAT. EXPECT A FEW INCHES OF
ELEVATED SNOWFALL ACROSS OR INTO NV AND THE SOUTHERN CA SIERRA ON
THURS, AS SNOW LEVELS GRADUALLY FALL WITH LOWER UPPER HEIGHTS. ON
FRI, A LARGE CLOSED 500 MB CIRCULATION WILL SPREAD DOWNSTREAM INTO
THE FOUR CORNERS REGION AND SHOULD YIELD SOME DYNAMICALLY DRIVEN
AND UPSLOPE SNOWFALL FROM THE SOUTHERN WASATCH INTO THE CO
ROCKIES, ESPECIALLY FOR THE SAN JUANS OF CO. THE CLOSED UPPER LOW
WILL EMERGE OUT OVER THE CENTRAL/SOUTHERN PLAINS ON SAT, WHILE
ENHANCED VERTICAL LIFT FROM THE PASSING MID-LEVEL LOW AND STEADY
UPSLOPE FLOW SHOULD CONTINUE TO PRODUCE HEAVY SNOW ACROSS CO
TERRAIN. PTYPE ISSUES BEGIN TO EMERGE ON SAT, AS A NUMBER OF
SOLUTIONS ALLOW SNOW TO SPREAD DOWN THE FOOTHILLS AND LEE SIDE OF
THE CENTRAL ROCKIES. WPC STAYED CLOSER TO THE SLOWER AND WARMER
ECMWF, WITH MASS FIELDS AND THERMALS.


...GREAT LAKES AND NEW YORK/NEW ENGLAND...

A DYNAMIC SHORT WAVE TROUGH PRODUCING HEAVY SNOW OVER IA/MN AND WI
THIS AFTERNOON WILL TRANSITION DOWNSTREAM TO THE GREAT LAKES INTO
NEW ENGLAND. A CLOSED MID TO UPPER LOW ACCOMPANYING THIS COMPACT
SYSTEM WILL BEGIN TO INTERACT WITH A DIGGING NORTHERN STREAM JET.
THE PARENT LOW STREAKING INTO THE NORTHERN MID-ATL STATES WILL
WEAKEN, WHILE A TRIPLE POINT
JUST OFFSHORE OF SOUTHERN NEW ENGLAND DEEPENS AND LIFTS INTO THE
CANADIAN MARITIMES. THIS SHOULD YIELD OVERALL A LIGHT STREAK OF
SNOW FROM NORTHERN IL/SOUTHERN WI THROUGH SOUTHERN LOWER
MI/NORTHERN IN/OH INTO NORTHERN PA/NY STATE AND NEW ENGLAND ON
THURS AND FRI. THE GUIDANCE SUGGESTS THE HEAVIEST SNOW POTENTIAL
ACROSS NORTHERN PA/SOUTHERN NY, NEAR THE STATE LINE ON THURS.

THE PROBABILITY OF FREEZING RAIN GREATER THAN 0.25 INCHES IS LESS
THAN 10 PERCENT DAYS 1-3.

MUSHER



$$




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------------=_1524126044-23415-262
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FOUS11 KWBC 190820
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
419 AM EDT THU APR 19 2018

VALID 12Z THU APR 19 2018 - 12Z SUN APR 22 2018


DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES...

FORECAST REMAINS GENERALLY UNCHANGED...WITH LOCALLY HEAVY MOUNTAIN
SNOW ACCUMULATIONS LIKELY ACROSS PORTIONS OF CENTRAL ROCKIES AS A
UPPER LEVEL LOW ROLLS ACROSS THE REGION OVER THE NEXT TWO DAYS.

AN UPPER LOW MOVING INTO CA THIS MORNING IS EXPECTED TO MOVE
ACROSS THE SIERRA INTO THE GREAT BASIN ON THU BEFORE REACHING THE
FOUR CORNERS REGION BY EARLY FRI. MOISTURE WILL BE LIMITED AT
FIRST...HOWEVER STRONG DYNAMICS MAY BE ENOUGH TO PRODUCE SOME
LOCALLY SIGNIFICANT ACCUMULATIONS ACROSS PORTIONS OF THE SIERRA
AND THE CENTRAL NV RANGES. BUT OVERALL...WIDESPREAD HEAVY
ACCUMULATIONS ARE NOT EXPECTED. BY EARLY FRI...FAVORABLE DYNAMICS
ALONG THE LEFT-EXIT REGION OF A STRENGTHENING JET MAY BEGIN TO
SUPPORT SOME HEAVY ACCUMULATIONS FURTHER EAST ACROSS THE SAN JUANS.

ON FRI...THE POTENTIAL FOR MORE WIDESPREAD HEAVY ACCUMULATIONS IS
EXPECTED TO INCREASE ACROSS THE CENTRAL ROCKIES AS THE UPPER LOW
MOVES FURTHER EAST AND BEGINS TO INTERACT WITH DEEPER MOISTURE
SURGING NORTH THROUGH THE HIGH PLAINS. WPC DAY 2 PROBABILITIES
(ENDING 12 UTC SAT) SHOW THE POTENTIAL FOR HEAVY MOUNTAIN SNOWS
ACROSS A LARGE EXTENT OF THE CENTRAL CO...NORTH-CENTRAL NM AND
SOUTHEASTERN WY RANGES.

SNOWS ARE EXPECTED TO QUICKLY DIMINISH BY EARLY SAT HOWEVER AS THE
UPPER LOW CONTINUES TO MOVE PROGRESSIVELY EAST ACROSS THE CENTRAL
AND SOUTHERN PLAINS.

FOR DAYS 1-3...THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES
IS LESS THAN 10 PERCENT.

PEREIRA



$$




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------------=_1524171738-23415-439
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FOUS11 KWBC 192102
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
501 PM EDT THU APR 19 2018

VALID 00Z FRI APR 20 2018 - 00Z MON APR 23 2018


DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES...

A STRONG CLOSED MID TO UPPER LOW, CENTERED NEAR SOUTHERN NV THIS
AFTERNOON, WILL DELIVER SNOW TO PARTS OF THE FOUR CORNERS REGION
ON FRI AND SAT. THE GLOBAL MODELS AND ENSEMBLES CAPTURE THIS
FEATURE RATHER WELL WITH OVERALL MINIMAL SPREAD, ESPECIALLY
CONCERNING THE PROGRESSION OF THIS LARGE SCALE FEATURE. THE SYSTEM
WILL THEN SLOWLY PROGRESS INTO THE FOUR CORNERS REGION ON FRI AND
THROUGH THE CENTRAL/SOUTHERN ROCKIES INTO THE CENTRAL/SOUTHERN
PLAINS SAT. ON FRI, THE LARGE CLOSED 500 MB CIRCULATION WILL YIELD
SOME DYNAMICALLY DRIVEN AND UPSLOPE SNOWFALL FROM THE SOUTHERN
WASATCH INTO THE CO ROCKIES, ESPECIALLY FOR THE SWRN SAN JUANS OF
CO. THEN ON SAT, ENHANCED VERTICAL LIFT FROM THE PASSING MID-LEVEL
LOW AND STEADY UPSLOPE FLOW SHOULD CONTINUE TO PRODUCE HEAVY SNOW
ACROSS CO TERRAIN AND PERHAPS SPREAD TO THE PALMER DIVIDE AND
CHEYENNE RIDGE. THIS IS WHERE PTYPE ISSUES BEGIN TO EMERGE, AS A
NUMBER OF SOLUTIONS ALLOW SNOW TO SPREAD DOWN THE FOOTHILLS AND
LEE SIDE OF THE CENTRAL ROCKIES. WPC STAYED CLOSER TO THE ECMWF
THAN ANYTHING ELSE, WITH MASS FIELDS AND THERMALS.


FOR DAYS 1-3...THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES
IS LESS THAN 10 PERCENT.

MUSHER



$$




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FOUS11 KWBC 200840
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
439 AM EDT FRI APR 20 2018

VALID 12Z FRI APR 20 2018 - 12Z MON APR 23 2018

DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES...

A STRONG CLOSED MID TO UPPER LOW, CENTERED NEAR THE
NEVADA/UTAH/ARIZONA BORDER EARLY THIS MORNING WILL DELIVER SNOW TO
PARTS OF THE FOUR CORNERS REGION AND CENTRAL/SOUTHERN ROCKIES FROM
LATER TODAY INTO THE DAY ON SATURDAY.

THE GLOBAL MODELS AND ENSEMBLES STILL CAPTURE THIS FEATURE RATHER
WELL WITH OVERALL MINIMAL SPREAD, ESPECIALLY CONCERNING THE
PROGRESSION OF THIS LARGE SCALE FEATURE. THE SYSTEM WILL THEN
SLOWLY PROGRESS INTO THE FOUR CORNERS REGION TODAY AND THEN
PROGRESS THROUGH THE CENTRAL/SOUTHERN ROCKIES INTO THE
CENTRAL/SOUTHERN PLAINS SAT.

THE LARGE CLOSED 500 MB CIRCULATION WILL YIELD SOME DYNAMICALLY
DRIVEN AND UPSLOPE SNOWFALL FROM THE SOUTHERN WASATCH INTO THE CO
ROCKIES TODAY AND TONIGHT, ESPECIALLY FOR THE SWRN SAN JUANS OF
CO. BY SATURDAY, ENHANCED VERTICAL LIFT FROM THE PASSING MID-LEVEL
LOW AND STEADY UPSLOPE FLOW SHOULD CONTINUE TO PRODUCE HEAVY SNOW
ACROSS CO TERRAIN AND PERHAPS SPREAD TO THE PALMER DIVIDE UP TO
THE CHEYENNE RIDGE.

THIS IS WHERE PTYPE ISSUES BEGIN TO EMERGE, AS A NUMBER OF
SOLUTIONS ALLOW SNOW TO SPREAD DOWN THE FOOTHILLS AND LEE SIDE OF
THE CENTRAL ROCKIES. WPC STAYED CLOSER TO THE ECMWF THAN ANYTHING
ELSE IN TERMS OF BOTH MASS FIELDS AND THERMALS.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

BANN



$$




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FOUS11 KWBC 202009
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 PM EDT FRI APR 20 2018

VALID 00Z SAT APR 21 2018 - 00Z TUE APR 24 2018

DAYS 1-3...

...CENTRAL ROCKIES...

A STRONG CLOSED MID TO UPPER LOW OVER THE FOUR CORNERS REGION IS
DELIVERING HEAVY SNOWFALL FOR THE CO TERRAIN THIS AFTERNOON. THIS
LARGE SCALE CIRCULATION WILL ADVANCE DOWNSTREAM AND ARRIVE INTO
THE CENTRAL TO SOUTHERN PLAINS ON SAT. THE GUIDANCE IS RATHER
UNANIMOUS IN A STEADY UPSLOPE COMPONENT REMAINING INTACT ACROSS CO
THAT SHOULD SUPPORT ADDITIONAL HEAVY SNOWFALL AMOUNTS. THE
UNCERTAINTY IN THE FORECAST IS WITH THERMALS AND WHETHER SNOWFALL
WILL SPREAD FROM THE CO ROCKIES OUT TO THE PALMER DIVIDE AND
CHEYENNE RIDGE. WPC TOOK A COMPROMISE OF THE ECMWF AND GFS FOR
PTYPE AND CARRIED MINIMAL SNOWFALL AMOUNTS.

...NORTHERN INTER-MOUNTAIN WEST...

AS A SHORT WAVE TROUGH MOVES THROUGH THE PAC NW TOWARD CENTRAL
CANADA, ADDITIONAL PAC DYNAMICS WILL REACH THE PAC NW, AMPLIFY AND
SLIDE THROUGH THE INTER-MOUNTAIN WEST LATE SUN THROUGH MON. THIS
SYSTEM WILL CAPITALIZE ON ENHANCED UPSLOPE FLOW FOR HEAVY SNOW
FROM CENTRAL ID THROUGH SOUTHERN MT INTO NORTHERN WY, WHICH
INCLUDES THE NORTHERN TETONS/ABSAROKA ND GIG HORN MTNS. WPC
FOLLOWED A BLEND OF THE ECMWF AND GFS THERMALS FOR HEAVY SNOW
PROBS.


THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

MUSHER



$$




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FOUS11 KWBC 210828
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
427 AM EDT SAT APR 21 2018

VALID 12Z SAT APR 21 2018 - 12Z TUE APR 24 2018

DAYS 1-3...

...CENTRAL ROCKIES...

A STRONG CLOSED MID/UPPER LEVEL LOW MAKING ITS WAY ACROSS THE
ROCKIES FRONT RANGE EARLY THIS MORNING WILL BE MOVING AWAY FROM
THE MOUNTAINS AND OUT OVER THE ADJACENT HIGH PLAINS. ANY
LINGERING SNOW OVER THE MOUNTAINS THIS MORNING SHOULD BE TAPERING
OFF QUICKLY WITH LITTLE THREAT OF ADDITIONAL MODERATE TO HEAVY
SNOWFALL.

...NORTHERN INTER-MOUNTAIN WEST...

AS A SHORT WAVE TROUGH MOVES THROUGH THE PAC NW TOWARD CENTRAL
CANADA, ADDITIONAL PAC DYNAMICS WILL REACH THE PAC NW, AMPLIFY AND
SLIDE THROUGH THE INTER-MOUNTAIN WEST LATE SUN THROUGH MON. THIS
SYSTEM WILL CAPITALIZE ON ENHANCED UPSLOPE FLOW FOR HEAVY SNOW
FROM PARTS OF ID INTO PARTS OF SOUTHWEST MT AND NORTHWEST
WY...INCLUDING THE NORTHERN TETONS/ABSAROKA AND BIG HORN MTNS. WPC
FOLLOWED A BLEND OF THE ECMWF AND GFS THERMALS FOR HEAVY SNOW
PROBS. SOME QUESTION REMAINS HOW FAR OUT OVER THE PLAINS THE
SNOWFALL WILL MAKE IT ON DAY 3. THINKING IS THAT TEMPERATURES
WILL BE TOO WARM FOR SNOW UP UNTIL THE LAST 6 TO PERHAPS 9
HOURS...23/03Z TO 23/12Z. CONSEQUENTLY...WE LEANED TOWARDS THE
GUIDANCE WITH LOWER NUMBERS.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

BANN





$$




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FOUS11 KWBC 211947
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
347 PM EDT SAT APR 21 2018

VALID 00Z SUN APR 22 2018 - 00Z WED APR 25 2018

DAYS 1-3...

...NORTHERN INTER-MOUNTAIN WEST TO NORTHERN HIGH PLAINS...

A SHORT WAVE TROUGH RACING ALONG THE NORTHERN TIER OF THE COUNTRY
TOWARD CENTRAL CANADA WILL BE FOLLOWED BY ADDITIONAL PAC DYNAMICS.
THIS STREAM OF UPPER DYNAMICS WILL PUSH THROUGH THE PAC NW,
AMPLIFY AND SLIDE THROUGH THE INTER-MOUNTAIN WEST LATE SUN THROUGH
MON BEFORE EMERGING INTO THE HIGH PLAINS. THIS SYSTEM WILL
CAPITALIZE ON ENHANCED UPSLOPE FLOW FOR HEAVY SNOW FROM SOUTHERN
MT AND NORTHERN WY...INCLUDING THE NORTHERN TETONS/ABSAROKA AND
BIG HORN MTNS, ON MON AND ACROSS EASTERN WY INTO WESTERN PORTIONS
OF SD/NE INCLUDING THE BLACK HILLS ON TUES. WPC FOLLOWED A BLEND
OF THE ECMWF AND GFS THERMALS FOR HEAVY SNOW PROBS ON MON BUT
REVERTED TO A COMPROMISE OF THE GUIDANCE FOR TUES. THIS IS DUE TO
SPREAD WITH THE GUIDANCE ON PROGRESSION OF THE SYSTEM ALOFT, WHICH
HAS CONSEQUENCES ON THE ADVANCEMENT OF SNOW SPREADING OUT INTO THE
PLAINS.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

MUSHER





$$




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Content-Type: text/plain

FOUS11 KWBC 220854
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
454 AM EDT SUN APR 22 2018

VALID 12Z SUN APR 22 2018 - 12Z WED APR 25 2018

DAYS 1-3...

...NORTHERN INTER-MOUNTAIN WEST TO NORTHERN HIGH PLAINS...

A WAVE RACING ALONG THE NORTHERN TIER OF THE COUNTRY TOWARD
CENTRAL CANADA WILL BE FOLLOWED BY ADDITIONAL DYNAMICS COMING IN
FROM THAT PACIFIC. THIS STREAM OF UPPER DYNAMICS WILL PUSH THROUGH
THE PAC NW, AMPLIFY AND SLIDE THROUGH THE INTER-MOUNTAIN WEST LATE
TONIGHT THROUGH MONDAY BEFORE EMERGING INTO THE HIGH PLAINS.

THIS SYSTEM WILL CAPITALIZE ON ENHANCED UPSLOPE FLOW FOR HEAVY
SNOW FROM SOUTHERN MT AND NORTHERN WY...INCLUDING THE NORTHERN
TETONS/ABSAROKA AND BIG HORN MTNS, ON MON AND ACROSS EASTERN WY
INTO WESTERN PORTIONS OF SD/NE INCLUDING THE BLACK HILLS ON TUES.

WPC FOLLOWED A BLEND OF THE ECMWF AND GFS THERMALS...WEIGHTED
SOMEWHAT MORE HEAVILY TOWARDS THE ECMWF...FOR HEAVY SNOW PROBS ON
MON BUT REVERTED TO A COMPROMISE OF THE GUIDANCE BY LATE TUESDAY.
THIS IS DUE TO CONTINUED SPREAD IN THE GUIDANCE WITH RESPECT TO
PROGRESSION OF THE SYSTEM ALOFT. THIS CLEARLY HAS CONSEQUENCES ON
THE ADVANCEMENT OF SNOW SPREADING OUT INTO THE PLAINS.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

BANN





$$




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Content-Type: text/plain

FOUS11 KWBC 221935
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
335 PM EDT SUN APR 22 2018

VALID 00Z MON APR 23 2018 - 00Z THU APR 26 2018

DAYS 1-3...

...NORTHERN INTER-MOUNTAIN WEST TO NORTHERN HIGH PLAINS...

UPPER DYNAMICS ORGANIZING OVER THE PAC NW AND ON THE TAIL END OF A
POLAR FRONTAL ZONE WILL STREAM THROUGH THE NORTHERN INTER-MOUNTAIN
WEST ON MONDAY BEFORE EMERGING OUT OVER THE NORTHERN TO CENTRAL
HIGH PLAINS. THIS SYSTEM WILL CAPITALIZE ON ENHANCED UPSLOPE FLOW
FOR HEAVY SNOW FROM SOUTHERN MT AND NORTHERN WY ON MON, INCLUDING
THE NORTHERN TETONS/ABSAROKA AND BIG HORN MTNS, AND ACROSS NERN
WY/SERN MT INTO WESTERN PORTIONS OF SD INCLUDING THE BLACK HILLS
ON TUES. WPC FOLLOWED A 50/50 BLEND OF THE ECMWF AND GFS THERMALS
FOR HEAVY SNOW PROBS, AS SPREAD WITH THE GUIDANCE HAS NARROWED.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

MUSHER





$$




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FOUS11 KWBC 230824
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
423 AM EDT MON APR 23 2018

VALID 12Z MON APR 23 2018 - 12Z THU APR 26 2018

DAYS 1-3...

...NORTHERN INTER-MOUNTAIN WEST TO ADJACENT HIGH PLAINS...

UPPER DYNAMICS ORGANIZING OVER THE PAC NW AND ON THE TAIL END OF A
POLAR FRONTAL ZONE WILL STREAM THROUGH THE NORTHERN INTER-MOUNTAIN
WEST THROUGHOUT THE DAY TODAY BEFORE EMERGING OUT OVER THE
NORTHERN TO CENTRAL HIGH PLAINS.

THIS SYSTEM WILL CAPITALIZE ON ENHANCED UPSLOPE FLOW FOR HEAVY
SNOW FROM SOUTHERN MT AND NORTHERN WY...INCLUDING THE NORTHERN
TETONS/ABSAROKA AND BIG HORN MTNS, AND ACROSS NERN WY/SERN
MT...BEFORE SPREADING INTO PORTIONS OF WESTERN SOUTH DAKOTA
INCLUDING THE BLACK HILLS ON TUES.

WPC FOLLOWED A BLEND OF THE ECMWF AND GFS THERMALS FOR HEAVY SNOW PROBS...ALTHOUGH THE NAM/ECMWF WAS GIVEN SOMEWHAT MORE WEIGHT THAN
THE GFS.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

BANN





$$




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FOUS11 KWBC 232015
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
414 PM EDT MON APR 23 2018

VALID 00Z TUE APR 24 2018 - 00Z FRI APR 27 2018

DAYS 1-3...

...NORTHERN ROCKIES TO ADJACENT HIGH PLAINS...

LATE SEASON SNOWFALL WILL CONTINUE WITH A WELL-DEFINED SHORTWAVE
DROPPING THROUGH THE NORTHERN ROCKIES MONDAY NIGHT. THE SYSTEM
WILL CONTINUE TO CAPITALIZE ON ENHANCED UPSLOPE FLOW, BRINGING
PERIODS OF HEAVY SNOW TO SOUTHEASTERN MONTANA AND NORTHEASTERN
WYOMING, BEFORE SINKING SOUTH INTO THE CENTRAL ROCKIES AND PLAINS
ON TUESDAY. THE GREATEST CHANCE FOR SNOWFALL ACCUMULATIONS TO
EXCEED 8-INCHES WILL BE ACROSS THE BLACK HILLS, WHERE WPC
PROBABILITIES ARE SHOWING A MODERATE RISK. SNOW WILL ALSO BE
POSSIBLE WITH AN UPSTREAM SHORTWAVE REACHING MONTANA ON WEDNESDAY,
BUT WPC PROBABILITIES CURRENTLY KEEP THE PROBABILITY OF SNOWFALL
ACCUMULATIONS TO EXCEED 4-INCHES LESS THAN 10 PERCENT.


GERHARDT





$$




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FOUS11 KWBC 232021
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
420 PM EDT MON APR 23 2018

VALID 00Z TUE APR 24 2018 - 00Z FRI APR 27 2018

DAYS 1-3...

...NORTHERN ROCKIES TO ADJACENT HIGH PLAINS...

LATE SEASON SNOWFALL WILL CONTINUE WITH A WELL-DEFINED SHORTWAVE
DROPPING THROUGH THE NORTHERN ROCKIES MONDAY NIGHT. THE SYSTEM
WILL CONTINUE TO CAPITALIZE ON ENHANCED UPSLOPE FLOW, BRINGING
PERIODS OF HEAVY SNOW TO SOUTHEASTERN MONTANA AND NORTHEASTERN
WYOMING, BEFORE SINKING SOUTH INTO THE CENTRAL ROCKIES AND PLAINS
ON TUESDAY. THE GREATEST CHANCE FOR SNOWFALL ACCUMULATIONS TO
EXCEED 8-INCHES WILL BE ACROSS THE BLACK HILLS, WHERE WPC
PROBABILITIES ARE SHOWING A MODERATE RISK. SNOW WILL ALSO BE
POSSIBLE WITH AN UPSTREAM SHORTWAVE REACHING MONTANA ON WEDNESDAY,
BUT WPC PROBABILITIES CURRENTLY KEEP THE PROBABILITY OF SNOWFALL
ACCUMULATIONS TO EXCEED 4-INCHES LESS THAN 10 PERCENT.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAYS 1-3.


GERHARDT





$$




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Content-Type: text/plain

FOUS11 KWBC 240851
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
451 AM EDT TUE APR 24 2018

VALID 12Z TUE APR 24 2018 - 12Z FRI APR 27 2018

DAYS 1 AND 2...

...NORTHERN ROCKIES TO ADJACENT HIGH PLAINS...

LATE SEASON SNOWFALL OVER PARTS OF THE HIGHER TERRAIN IN WESTERN
SOUTH DAKOTA THIS MORNING AS A WELL-DEFINED SHORTWAVE DROPS
SOUTHEAST INTO THE REGION. THE SYSTEM SHOULD THEN LOSE ANY UPSLOPE
FLOW AT THE SAME TIME IT HEADS INTO A WARMER AIRMASS.

AN ADDITIONAL AREA OF LIGHT SNOW IS POSSIBLE IN THE UPSLOPE
REGIONS OF MOUNTAINS IN NORTHERN/CENTRAL COLORADO ONCE LOW LEVEL
WINDS TURN TO THE NORTH/NORTHEAST AND THE REGION GETS BRUSHED BY
THE SOUTHERN EDGE OF THE SHORTWAVE TROUGH MENTIONED ABOVE.
INITIALLY THE LOW LEVELS OVER THE PLAINS SHOULD BE TOO DRY TO
SUPPORT MUCH IN THE WAY OF POST FRONTAL ACCUMULATION.

GENERALLY LIGHT SNOW WILL ALSO BE POSSIBLE OVER PARTS OF MONTANA
AND WYOMING ON WEDNESDAY AS AN UPSTREAM SHORTWAVE APPROACHES THE
REGION. THE AMOUNT OF MOISTURE AVAILABLE WILL BE LIMITED.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT.

DAY 3...

THE PROBABILITY OF HEAVY SNOW OR ICING GREATER THAN 0.25 INCHES IS
LESS THAN 10 PERCENT.

BANN





$$




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FOUS11 KWBC 241915
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 PM EDT TUE APR 24 2018

VALID 00Z WED APR 25 2018 - 00Z SAT APR 28 2018

...DAY 1...

...CO SANGRE DE CRISTO MOUNTAINS...

AN AREA OF LIGHT SNOW IS EXPECTED IN THE UPSLOPE REGIONS OF THE
SANGRE DE CRISTO MOUNTAINS OF SOUTHEAST CO TO THE NM BORDER AS
COMBINED BOUNDARY LAYER CONVERGENCE/300 MB DIVERGENCE AND RELATIVE
HUMIDITY OF 90 PERCENT OVERLAP WITH ASCENT THIS EVENING AS A 700
MB WAVE PASSES ACROSS THE REGION. THE PASSAGE OF THE WAVE AND JET
MAXIMA LATE TONIGHT IS FOLLOWED BY A PERIOD OF DRYING ALOFT AND
CESSATION OF LIFT...WHICH SHOULD BRING THE SNOW TO AN END.


..DAY 2...

...WY BIGHORN MOUNTAINS...

LIGHT SNOW IS EXPECTED OVER THE BIGHORN MOUNTAINS OF WYOMING ON
WEDNESDAY EVENING AS AN UPSTREAM SHORTWAVE APPROACHES THE
REGION....WITH LIFT PROVIDED BY 300 MB DIVERGENCE IN THE LEFT EXIT
REGION OF THE JET STREAM. THIS COINCIDES WITH MODEST LOW LEVEL
CONVERGENCE WITH THE FRONT AND POST-FRONTAL UPSLOPE FLOW AS WINDS
VEER TO THE NORTHWEST. THE SNOW SHOULD TAPER THU AS THE JET AND
MOISTURE POOL MOVES AWAY FROM THE REGION.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT DAYS 1-2.

DAY 3...

THE PROBABILITY OF HEAVY SNOW AND/OR ICING GREATER THAN 0.25
INCHES IS LESS THAN 10 PERCENT.

PETERSEN






$$




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------------=_1524724263-23415-2101
Content-Type: text/plain

FOUS11 KWBC 260630
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
230 AM EDT THU APR 26 2018

VALID 12Z THU APR 26 2018 - 12Z SUN APR 29 2018

...MINNESOTA ARROWHEAD...

A MID LEVEL TROUGH AND AN ASSOCIATED SURFACE COLD FRONT WILL MOVE
ACROSS SOUTHERN CANADA, WITH POST-FRONTAL COLD ADVECTION CHANGING
PRECIPITATION OVER TO SEVERAL HOURS OF WET SNOW. SOME LIGHT
ACCUMULATIONS APPROACHING AN INCH ARE POSSIBLE ON GRASSY SURFACES
IN THE NORTHERN PORTION OF THE MINNESOTA ARROWHEAD REGION THURSDAY
NIGHT.

...RANGES OF NORTHERN CALIFORNIA AND THE CASCADES...

THE MAIN FEATURE OF INTEREST WILL BE A LARGE CLOSED UPPER LOW
SLOWLY PROGRESSING EASTWARD OVER NORTHERN CALIFORNIA AND OREGON
FRIDAY NIGHT AND INTO SATURDAY. COLD AIR ADVECTION AND STEEP
LAPSE RATES OWING TO RAPIDLY COOLING 500-700MB TEMPERATURES WILL
RESULT IN SNOW LEVELS FALLING TO 4000 TO 6000 FEET, AND THE RESULT
WILL BE CONVECTIVE SNOW SHOWERS FOR THE HIGHEST ELEVATIONS OF THE
SISKIYOUS, SHASTA, AND CASCADES. THERE SHOULD BE ENOUGH MOISTURE
AND LIFT AVAILABLE TO SUPPORT 1 TO 2 INCH AMOUNTS, AND POSSIBLY
GREATEST FOR THE HIGHEST SUMMITS.

...IDAHO ROCKIES...

WITH THE CLOSED LOW IMPINGING ON THE NORTHERN ROCKIES BY DAY 3
(SATURDAY NIGHT), DEEP LAYER ASCENT AHEAD OF THE LOW WITH A
SHORTWAVE DISTURBANCE PIVOTING AROUND IT IS EXPECTED TO LEAD TO
MODERATE SNOW OVER THE HIGHER ELEVATIONS OF THE SALMON RIVER AND
SAWTOOTH MOUNTAINS, AND SOME ALSO EXTENDING INTO THE BITTERROOT
RANGE. THIS REGION HAS THE HIGHEST CHANCE OF RECEIVING GREATER
THAN 4 INCHES ANYWHERE NATIONWIDE DURING THE ENTIRE FORECAST
PERIOD, MAINLY ABOVE 6000 FEET.

ELSEWHERE, THERE IS ALSO SOME MODEL SIGNAL FOR LIGHT SNOW OVER THE
HIGHEST ELEVATIONS OF THE SAN JUAN MOUNTAINS OF COLORADO FROM
FRIDAY NIGHT THROUGH SATURDAY.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3 NATIONWIDE.

HAMRICK







$$




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FOUS11 KWBC 261946
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EDT THU APR 26 2018

VALID 00Z FRI APR 27 2018 - 00Z MON APR 30 2018


...RANGES OF NORTHERN CALIFORNIA AND THE CA/OR/WA CASCADES...

A LARGE CLOSED UPPER LOW IS FORECAST TO SLOWLY PROGRESS EASTWARD
OVER OREGON FRIDAY NIGHT AND INTO SATURDAY. COLD AIR ADVECTION
AND STEEP LAPSE RATES OWING TO RAPIDLY COOLING 500-700MB
TEMPERATURES WILL RESULT IN SNOW LEVELS FALLING TO 4000 TO 6000
FEET, AND THE RESULT WILL BE CONVECTIVE SNOW SHOWERS FOR THE
HIGHEST ELEVATIONS OF THE SISKIYOUS, SHASTA, AND CA/OR/WA
CASCADES. THERE SHOULD BE ENOUGH MOISTURE AND LIFT AVAILABLE TO
SUPPORT 1 TO 3 INCH AMOUNTS, WITH SEVERAL INCHES POSSIBLE IN
ISOLATED PEAKS.

...NORTHERN ROCKIES...

WITH THE 700 MB CLOSED LOW CROSSING THE NORTHERN ROCKIES SATURDAY
NIGHT AND SUNDAY, DEEP LAYER ASCENT AHEAD OF THE LOW WITH A
SHORTWAVE DISTURBANCE PIVOTING AROUND IT IS EXPECTED TO LEAD TO
SEVERAL INCHES OF SNOW OVER THE HIGHER ELEVATIONS OF THE SALMON
RIVER AND SAWTOOTH MOUNTAINS, CONTINUING ACROSS THE BITTERROOT
RANGE AND EVENTUALLY INTO THE RANGES OF NORTHWEST MT. THIS REGION
HAS THE HIGHEST CHANCE OF RECEIVING GREATER THAN 4 INCHES. THERE
ARE STILL LATITUDINAL DIFFERENCES WITH THE TRACK OF THE
CIRCULATION WITH THE NAM AND UKMET TRENDING NORTH TOWARDS THE GFS
AND ECMWF SOLUTIONS.

ELSEWHERE, THERE IS ALSO MODEL SIGNAL FOR LIGHT SNOW OVER THE
HIGHEST ELEVATIONS OF THE SAN JUAN MOUNTAINS OF COLORADO FROM
FRIDAY NIGHT THROUGH SATURDAY.

...NEW YORK ADIRONDACKS...

THE MODELS FORECAST A MID-UPPER LEVEL LOW TO CROSS THE GREAT LAKES
SAT AND NEW YORK-NORTHERN NEW ENGLAND SUNDAY. AS THE LOW MOVES
EAST....FALLING HEIGHTS/TEMPS ALLOW PRECIP TO CHANGE OVER TO SNOW
IN THE NY ADIRONDACK MOUNTAINS. A FEW INCHES ARE EXPECTED SUN AS
POST-FRONTAL NORTHWEST WINDS PROVIDE UPSLOPE FLOW IN WINDWARD
FACING TERRAIN. THE MODELS ARE COMING INTO BETTER AGREEMENT ON
THE TIMING OF THE 700-500 MB LOW SO WEIGHTING AMONG SOLUTIONS WAS
SIMILAR.

...MINNESOTA ARROWHEAD...

A MID LEVEL TROUGH AND AN ASSOCIATED SURFACE COLD FRONT WILL MOVE
ACROSS NORTHERN MN, WITH POST-FRONTAL COLD ADVECTION CHANGING
PRECIPITATION OVER TO WET SNOW. SOME LIGHT ACCUMULATIONS NEAR AN
INCH ARE POSSIBLE ON GRASSY SURFACES IN THE NORTHERN PORTION OF
THE MINNESOTA ARROWHEAD REGION TONIGHT.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

PETERSEN









$$




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FOUS11 KWBC 270812
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 AM EDT FRI APR 27 2018

VALID 12Z FRI APR 27 2018 - 12Z MON APR 30 2018

NORTHERN ROCKIES...

A CLOSED MID TO UPPER LEVEL LOW AND AN ASSOCIATED COLD FRONT WILL
SLOWLY MAKE ITS WAY INLAND ACROSS THE PACIFIC NORTHWEST AND THEN
EVOLVING INTO A LONG WAVE TROUGH BY THE END OF THE FORECAST PERIOD
MONDAY MORNING. DEEP LAYER ASCENT AHEAD OF THE LOW WITH A
SHORTWAVE DISTURBANCE PIVOTING AROUND IT IS EXPECTED TO LEAD TO
SEVERAL INCHES OF SNOW OVER THE HIGHER ELEVATIONS OF THE SALMON
RIVER AND SAWTOOTH MOUNTAINS, CONTINUING ACROSS THE BITTERROOT
RANGE AND EVENTUALLY INTO THE RANGES OF NORTHWEST MONTANA. THIS
REGION HAS THE HIGHEST CHANCE OF RECEIVING GREATER THAN 4 INCHES
OF SNOW ON DAY 3. A NON-CMC COMPROMISE WORKED WELL FOR THE
THERMAL PROFILES SINCE THE CMC WAS FARTHER SOUTH THAN THE MODEL
CONSENSUS.


NEW YORK ADIRONDACKS...

THE MODELS FORECAST A MID-UPPER LEVEL LOW TO CROSS THE GREAT LAKES
ON SATURDAY AND THEN NORTHERN NEW ENGLAND ON SUNDAY. AS THE LOW
MOVES EAST, FALLING HEIGHTS/TEMPS ALLOW PRECIPITATION TO CHANGE
OVER TO SNOW FOR THE NEW YORK ADIRONDACK MOUNTAINS. A FEW INCHES
OF ACCUMULATION ARE POSSIBLE ON DAY 3 AS POST-FRONTAL NORTHWEST
WINDS PROVIDE UPSLOPE FLOW OVER WINDWARD FACING TERRAIN,
ESPECIALLY ABOVE 3000 FEET. THE MODELS ARE COMING INTO BETTER
AGREEMENT ON THE TIMING OF THE MID-LEVEL LOW, AND THEREFORE A
BLEND OF THE ECMWF/GFS/EC MEAN WAS USED FOR THE THERMAL PROFILES.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

HAMRICK









$$




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------------=_1524857383-23415-2403
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FOUS11 KWBC 271929
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 PM EDT FRI APR 27 2018

VALID 00Z SAT APR 28 2018 - 00Z TUE MAY 01 2018

NORTHERN ROCKIES...

A CLOSED UPPER LEVEL LOW AND AN ASSOCIATED COLD FRONT OVER THE
PACIFIC NORTHWEST SATURDAY WILL EVOLVE INTO A LONG WAVE TROUGH
OVER THE INTERMOUNTAIN WEST SUNDAY. DEEP LAYER ASCENT AHEAD OF THE
LOW WITH A SHORTWAVE DISTURBANCE PIVOTING AROUND WILL RESULT IN
LOCALLY HEAVY SNOW OVER THE HIGHER MOUNTAINS OF OR/WA/ID SUNDAY
AND UT/ID/MY/WY MONDAY. THE THERMAL PROFILE IS BASED ON A BLEND OF
THE 12Z GFS/NAM AND 00Z ECMWF WITH LOCATIONS/TOTALS ADJUSTED BASED
ON THE DOWNSCALED 5KM MULTI-MODEL ENSEMBLE BLEND FROM WPC.


NEW YORK ADIRONDACKS...

A MID-UPPER LEVEL LOW WILL CROSS THE GREAT LAKES ON SATURDAY AND
THEN NORTHERN NEW ENGLAND ON SUNDAY. AS THE LOW MOVES EAST,
FALLING HEIGHTS/TEMPS ALLOW PRECIPITATION TO CHANGE OVER TO SNOW
FOR THE NEW YORK ADIRONDACK MOUNTAINS. A FEW INCHES OF
ACCUMULATION ARE LIKELY SUNDAY INTO MONDAY AS POST-FRONTAL
NORTHWEST WINDS PROVIDE UPSLOPE FLOW OVER WINDWARD FACING TERRAIN,
ESPECIALLY ABOVE 3000 FEET. DECENT AGREEMENT ON THE TIMING OF THE
MID-LEVEL LOW ALLOWED A BLEND OF THE ECMWF/GFS/NAM FOR THE THERMAL
PROFILES.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

JACKSON









$$




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------------=_1524897646-23415-2486
Content-Type: text/plain

FOUS11 KWBC 280640
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 AM EDT SAT APR 28 2018

VALID 12Z SAT APR 28 2018 - 12Z TUE MAY 1 2018

NORTHERN ROCKIES

THE MAIN WINTER WEATHER MAKER OVER THE NORTHWESTERN QUADRANT OF
THE NATION WILL BE A CLOSED UPPER LEVEL LOW OVER THE PACIFIC
NORTHWEST SATURDAY THAT WILL BE PROGRESSING SLOWLY EASTWARD. THIS
IS FORECAST TO EVOLVE INTO A LONG WAVE TROUGH OVER THE
INTERMOUNTAIN WEST BY SUNDAY NIGHT AND INTO MONDAY. DEEP LAYER
ASCENT AHEAD OF THE LOW, LEFT EXIT JET DYNAMICS, AND LOWERING
HEIGHTS ALOFT WITH A SHORTWAVE PASSING THROUGH WILL RESULT IN
LOCALLY HEAVY SNOW OVER THE HIGHER MOUNTAINS OF IDAHO, WESTERN
MONTANA, AND WESTERN AND CENTRAL WYOMING. THE HEAVIEST
ACCUMULATIONS ARE EXPECTED FROM SUNDAY NIGHT THROUGH MONDAY, WITH
MANY ENSEMBLE MEMBERS INDICATING THE POTENTIAL FOR AT LEAST 4
INCHES OF SNOW, AND SOME ARE SHOWING OVER 8 INCHES, PARTICULARLY
FOR THE ABSAROKA, WIND RIVER, AND BIG HORN MOUNTAINS. THE THERMAL
PROFILE IS BASED ON A BLEND OF THE 00Z GFS/NAM AND 12Z ECMWF WITH
LOCAL ADJUSTMENTS FOR TERRAIN.


NORTHEAST U.S.

A PRONOUNCED NORTHERN STREAM TROUGH OVER THE NORTHERN GREAT LAKES
ON SATURDAY IS FORECAST TO EVOLVE INTO A CLOSED UPPER LOW OVER NEW
ENGLAND BY SUNDAY, AND THEN MOVING OFFSHORE BY MONDAY NIGHT. AS
THE LOW MOVES EAST, FALLING HEIGHTS AND LOWERING FREEZING LEVELS
WILL ALLOW PRECIPITATION TO CHANGE OVER TO SNOW FOR THE NEW YORK
ADIRONDACK MOUNTAINS, AND PROBABLY FOR SOME OF THE CATSKILL
MOUNTAINS AND NORTHERN VERMONT AND NEW HAMPSHIRE AS WELL. A FEW
INCHES OF ACCUMULATION ARE LIKELY SUNDAY INTO MONDAY AS
POST-FRONTAL NORTHWEST WINDS PROVIDE UPSLOPE FLOW OVER WINDWARD
FACING TERRAIN, ESPECIALLY ABOVE 3000 FEET. DECENT AGREEMENT ON
THE TIMING OF THE MID-LEVEL LOW JUSTIFIED A BLEND OF THE
ECMWF/GFS/NAM FOR THE THERMAL PROFILES.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

D. HAMRICK









$$




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FOUS11 KWBC 292040
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
440 PM EDT SUN APR 29 2018

VALID 00Z MON APR 30 2018 - 00Z THU MAY 03 2018

...ROCKY MOUNTAINS AND RANGES OF THE GREAT BASIN...

ON SUNDAY NIGHT-MONDAY...AN AMPLIFYING UPPER LEVEL TROUGH CROSSING
ID AND NV INTO UT
PROVIDES UPPER LEVEL DIVERGENCE MAXIMA THAT INDUCES SYNOPTIC
SCALE ASCENT AHEAD OF THE THE UPPER TROUGH AXIS THAT PRODUCES SNOW
IN THE RANGES OVER SOUTHWEST MT/SOUTHERN ID...WHERE SEVERAL INCHES
MAY OCCUR.

A SHORTWAVE DISTURBANCE TRACKING AROUND THE AFOREMENTIONED UPPER
LOW IS EXPECTED TO RESULT IN A CLOSED 700 MB LOW DEVELOPING OVER
NORTHERN UTAH AND INTO WYOMING BY MONDAY MORNING. THE COMBINATION
OF STRONG 700MB FRONTOGENETICAL FORCING, LEFT EXIT JET DYNAMICS,
AND BOUNDARY LAYER UPSLOPE FLOW IS EXPECTED TO RESULT IN AREAS OF
MODERATE TO HEAVY LATE SEASON SNOW FROM THE NORTHERN WASATCH AND
UINTA MOUNTAINS OF UTAH INTO THE ABSAROKA, WIND RIVER, AND BIG
HORN MOUNTAINS OF WYOMING. THE POTENTIAL EXISTS FOR ACCUMULATIONS
OF 12-18 INCHES MONDAY THROUGH TUESDAY. THE SNOW TAPERS AS THE
700 MB LOW OR WAVE EJECTS NORTHEAST ACROSS THE NORTHERN PLAINS TUE.

LATER TUESDAY A CLOSED LOW IS FORECAST TO DEVELOP AT THE BASE OF
THE TROUGH OVER THE SOUTHWEST US. DEVELOPMENT OF COUPLED UPPER DIVERGENCE/LOWER CONVERGENCE MAXIMA IN THE VICINITY OF THE LOW-MID
LEVEL FRONT AS IT CROSSES THE CA SIERRA NEVADA MOUNTAINS TUE
CONTINUE DOWNSTREAM IN TANDEM WITH THE FRONT ACROSS NV AND THEN
THE UT WASATCH MOUNTAINS.
THE 12Z NAM SHOW POTENTIAL FOR AN INCH LIQUID EQUIVALENT IN THE
FORM OF SNOW IN THE UT UINTAS AND ISOLATED PEAKS OF THE
WASATCH...INDICATING POTENTIAL FOR ANOTHER HEAVY SNOW EVENT TO
DEVELOP. BOTH THE GFS AND ECMWF SHOW 300 MB DIVERGENCE DEVELOPING
IN NORTHERN CO WED AFTERNOON IN NORTHERN CO IN THE LEFT EXIT
REGION OF THE UPPER JET IN SOUTHEAST CO...SO SNOW SHOULD BE
INCREASING IN CONVERGE/INTENSITY THEN.

THE QPF AND THERMAL PROFILES WERE BASED ON A BLEND OF THE 12Z GFS/NAM/ECMWF/UKMET.

...NEW YORK/VERMONT...

A CLOSED UPPER LOW OVER NORTHERN NEW YORK AND SHOULD CROSSING NEW
ENGLAND TONIGHT, BEFORE MOVING OFFSHORE BY MONDAY EVENING. SNOW
HAS BEEN FALLING IN THE NEW YORK ADIRONDACK MOUNTAINS TODAY INTO
SARANAC LAKE NY AND SNOW SHOWERS SHOULD CONTINUE WITHIN THE MID
LEVEL DEFORMATION ZONE TONIGHT INTO MONDAY AND 700 MB VERTICAL
VELOCITY MAXIMA CONTINUING...WITH LOCALLY SEVERAL INCHES POSSIBLE.
A FEW INCHES OF ACCUMULATION ARE LIKELY TONIGHT INTO EARLY MONDAY
IN THE SOUTHERN GREEN MOUNTAINS OF VT AND ALSO THE CATSKILL
MOUNTAINS OF NY AS PERSISTENT DEEP MOISTURE TO AROUND 500 MB
REMAINS IN PLACE WITH NORTHWEST LOW LEVEL WINDS PROVIDING
LOCALIZED UPSLOPE FLOW IN WINDWARD TERRAIN.

COVERAGE IS FORECAST TO DROP QUICKLY MON AS DRIER AIR ALOFT
ADVECTS AROUND THE LOW AND THE DEPARTURE OF THE LOW REMOVES THE
LIFT.

DECENT AGREEMENT ON THE TIMING OF THE MID-LEVEL LOW LED TO A BLEND
OF THE ECMWF/GFS/NAM FOR BOTH QPF AND THE THERMAL PROFILES.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

PETERSEN









$$




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FOUS11 KWBC 292042
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
441 PM EDT SUN APR 29 2018

VALID 00Z MON APR 30 2018 - 00Z THU MAY 03 2018

...ROCKY MOUNTAINS AND RANGES OF THE GREAT BASIN...

ON SUNDAY NIGHT-MONDAY...AN AMPLIFYING UPPER LEVEL TROUGH CROSSING
ID AND NV INTO UT
PROVIDES UPPER LEVEL DIVERGENCE MAXIMA THAT INDUCES SYNOPTIC
SCALE ASCENT AHEAD OF THE THE UPPER TROUGH AXIS THAT PRODUCES SNOW
IN THE RANGES OVER SOUTHWEST MT/SOUTHERN ID...WHERE SEVERAL INCHES
MAY OCCUR.

A SHORTWAVE DISTURBANCE TRACKING AROUND THE AFOREMENTIONED UPPER
LOW IS EXPECTED TO RESULT IN A CLOSED 700 MB LOW DEVELOPING OVER
NORTHERN UTAH AND INTO WYOMING BY MONDAY MORNING. THE COMBINATION
OF STRONG 700MB FRONTOGENETICAL FORCING, LEFT EXIT JET DYNAMICS,
AND BOUNDARY LAYER UPSLOPE FLOW IS EXPECTED TO RESULT IN AREAS OF
MODERATE TO HEAVY LATE SEASON SNOW FROM THE NORTHERN WASATCH AND
UINTA MOUNTAINS OF UTAH INTO THE ABSAROKA, WIND RIVER, AND BIG
HORN MOUNTAINS OF WYOMING. THE POTENTIAL EXISTS FOR ACCUMULATIONS
OF 12-18 INCHES MONDAY THROUGH TUESDAY. THE SNOW TAPERS AS THE
700 MB LOW OR WAVE EJECTS NORTHEAST ACROSS THE NORTHERN PLAINS TUE.

LATER TUESDAY A CLOSED LOW IS FORECAST TO DEVELOP AT THE BASE OF
THE TROUGH OVER THE SOUTHWEST US. DEVELOPMENT OF COUPLED UPPER DIVERGENCE/LOWER CONVERGENCE MAXIMA IN THE VICINITY OF THE LOW-MID
LEVEL FRONT AS IT CROSSES THE CA SIERRA NEVADA MOUNTAINS TUE
CONTINUE DOWNSTREAM IN TANDEM WITH THE FRONT ACROSS NV AND THEN
THE UT WASATCH MOUNTAINS.
THE 12Z NAM SHOW POTENTIAL FOR AN INCH LIQUID EQUIVALENT IN THE
FORM OF SNOW IN THE UT UINTAS AND ISOLATED PEAKS OF THE
WASATCH...INDICATING POTENTIAL FOR ANOTHER HEAVY SNOW EVENT TO
DEVELOP. BOTH THE GFS AND ECMWF SHOW 300 MB DIVERGENCE DEVELOPING
IN NORTHERN CO WED AFTERNOON IN NORTHERN CO IN THE LEFT EXIT
REGION OF THE UPPER JET IN SOUTHEAST CO...SO SNOW SHOULD BE
INCREASING IN CONVERGE/INTENSITY THEN.

THE QPF AND THERMAL PROFILES WERE BASED ON A BLEND OF THE 12Z GFS/NAM/ECMWF/UKMET.

...NEW YORK/VERMONT...

A CLOSED UPPER LOW OVER NORTHERN NEW YORK AND SHOULD CROSSING NEW
ENGLAND TONIGHT, BEFORE MOVING OFFSHORE BY MONDAY EVENING. SNOW
HAS BEEN FALLING IN THE NEW YORK ADIRONDACK MOUNTAINS TODAY INTO
SARANAC LAKE NY AND SNOW SHOWERS SHOULD CONTINUE WITHIN THE MID
LEVEL DEFORMATION ZONE TONIGHT INTO MONDAY AND 700 MB VERTICAL
VELOCITY MAXIMA CONTINUING...WITH LOCALLY SEVERAL INCHES POSSIBLE.
A FEW INCHES OF ACCUMULATION ARE LIKELY TONIGHT INTO EARLY MONDAY
IN THE SOUTHERN GREEN MOUNTAINS OF VT AND ALSO THE CATSKILL
MOUNTAINS OF NY AS PERSISTENT DEEP MOISTURE TO AROUND 500 MB
REMAINS IN PLACE WITH NORTHWEST LOW LEVEL WINDS PROVIDING
LOCALIZED UPSLOPE FLOW IN WINDWARD TERRAIN.

COVERAGE IS FORECAST TO DROP QUICKLY MON AS DRIER AIR ALOFT
ADVECTS AROUND THE LOW AND THE DEPARTURE OF THE LOW REMOVES THE
LIFT.

DECENT AGREEMENT ON THE TIMING OF THE MID-LEVEL LOW LED TO A BLEND
OF THE ECMWF/GFS/NAM FOR BOTH QPF AND THE THERMAL PROFILES.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

PETERSEN









$$




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------------=_1524987983-23415-2680
Content-Type: text/plain

FOUS11 KWBC 290746
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 AM EDT SUN APR 29 2018

VALID 12Z SUN APR 29 2018 - 12Z WED MAY 02 2018

ROCKY MOUNTAINS

THE MAIN WINTER WEATHER MAKER OVER THE NORTHWESTERN QUADRANT OF
THE NATION WILL BE AN AMPLIFYING UPPER LEVEL TROUGH WITH MULTIPLE
SHORTWAVE PERTURBATIONS WITHIN IT THROUGH TUESDAY NIGHT. THE
FIRST FEATURE OF INTEREST IS A CLOSED UPPER LEVEL LOW OVER THE
PACIFIC NORTHWEST SUNDAY MORNING THAT IS FORECAST TO EVOLVE INTO A
LONG WAVE TROUGH OVER THE INTERMOUNTAIN WEST BY MONDAY MORNING.
SYNOPTIC SCALE ASCENT AHEAD OF THIS FEATURE AND LOWERING HEIGHTS
ALOFT IS EXPECTED TO RESULT IN LIGHT TO MODERATE SNOW SHOWERS OVER
THE HIGHER MOUNTAINS OF CENTRAL IDAHO AND SOUTHWESTERN MONTANA ON
DAY 1 (SUNDAY INTO SUNDAY NIGHT), AND ALSO THE HIGHEST ELEVATIONS
OF THE CASCADES.

A SHORTWAVE DISTURBANCE TRACKING AROUND THE AFOREMENTIONED UPPER
LOW IS EXPECTED TO RESULT IN A CLOSED 700MB LOW DEVELOPING OVER
NORTHERN UTAH AND INTO WYOMING BY THE BEGINNING OF THE DAY 2
PERIOD MONDAY MORNING, WITH THE 00Z GFS INDICATING THE GREATEST
REFLECTION OF THIS FEATURE. THE COMBINATION OF STRONG 700MB
FRONTOGENETICAL FORCING, LEFT EXIT JET DYNAMICS, AND BOUNDARY
LAYER UPSLOPE FLOW IS EXPECTED TO RESULT IN SIGNIFICANT LATE
SEASON SNOW FROM THE NORTHERN WASATCH AND UINTA MOUNTAINS OF UTAH,
AND PARTICULARLY THE ABSAROKA, WIND RIVER, AND BIG HORN MOUNTAINS
OF WYOMING. THE POTENTIAL EXISTS FOR ACCUMULATIONS IN EXCESS OF
12 INCHES, AND SOME ENSEMBLE MEMBERS ARE INDICATING THIS SCENARIO.
THE THERMAL PROFILE IS BASED ON A BLEND OF THE 00Z GFS/NAM AND
12Z ECMWF WITH LOCAL ADJUSTMENTS FOR TERRAIN.


NORTHEAST U.S.

A PRONOUNCED NORTHERN STREAM TROUGH IS IN THE PROCESS OF EVOLVING
INTO A CLOSED UPPER LOW OVER UPSTATE NEW YORK AND SHOULD DEVELOP
FURTHER WHILE CROSSING NEW ENGLAND SUNDAY NIGHT, BEFORE MOVING
OFFSHORE BY MONDAY EVENING. FALLING HEIGHTS AND LOWERING FREEZING
LEVELS WILL ALLOW PRECIPITATION TO CHANGE OVER TO SNOW FOR THE NEW
YORK ADIRONDACK MOUNTAINS, AND PROBABLY FOR SOME OF THE CATSKILL
MOUNTAINS AND NORTHERN VERMONT AND NEW HAMPSHIRE AS WELL. A FEW
INCHES OF ACCUMULATION ARE LIKELY SUNDAY INTO EARLY MONDAY AS
POST-FRONTAL NORTHWEST WINDS PROVIDE UPSLOPE FLOW OVER WINDWARD
FACING TERRAIN, ESPECIALLY ABOVE 3000 FEET. THERE IS SOME
ENSEMBLE SUPPORT FOR LOCAL 4+ INCH AMOUNTS. DECENT AGREEMENT ON
THE TIMING OF THE MID-LEVEL LOW JUSTIFIED A BLEND OF THE
ECMWF/GFS/NAM FOR THE THERMAL PROFILES.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

D. HAMRICK









$$




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FOUS11 KWBC 282040
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
439 PM EDT SAT APR 28 2018

VALID 00Z SUN APR 29 2018 - 00Z WED MAY 02 2018

RANGES OF PACIFIC NORTHWEST TO THE NORTHERN ROCKIES

HEAVY SNOW IS EXPECTED TO DEVELOP OVER THE RANGES NEAR THE
SOUTHWEST MT/ID BORDER AND ACROSS THE WIND RIVER/ABSAROKA/BIGHORN
MOUNTAINS OF WY. THERE IS POTENTIAL FOR 1-2 FEET IN THE MOUNTAINS
OF WESTERN AND NORTHERN WY.

THE CLOSED UPPER LEVEL LOW OVER THE PACIFIC NORTHWEST PROGRESSES
SLOWLY EASTWARD. PRECIP AMOUNTS ARE ON THE ORDER OF A QUARTER TO
LOCALLY HALF AN INCH IN THE RANGES OF WESTERN OR TO NORTHERN CA
AND SOUTHERN ID...SO NY HEAVY SOW WILL BE ISOLATED.

AMOUNTS PICK UP SUNDAY NIGHT AS AN UPPER TROUGH ROTATING
UNDERNEATH THE CLOSED LOW CROSSES FROM NV THROUGH NORTHERN UT AND
INTO ADJACENT ID AND WESTERN WY. ENHANCED UPPER DIVERGENCE IN
ADVANCE OF THE APPROACHING WAVE FOCUSES HEAVY SNOW AT HIGHER
ELEVATIONS OF THE UT UINTAS INTO THE MOUNTAINS OF WESTERN WY. THE
WIND RIVER MOUNTAINS ARE A FOCUS AS A FEW MODELS INDICATE A LARGE
300 MB DIVERGENCE/700 MB CONVERGENCE MAXIMA SUN ON MONDAY.

THE NAM/GFS SHOW THE 700 MB WAVE AND POTENTIAL FOR A CLOSED LOW TO
DEVELOP OVER WY AS THE FOCUS FOR MODERATE TO HEAVY SNOW CONTINUING
INTO SUNDAY NIGHT BEFORE THE WAVE DEPARTS AND COLD FRONT MOVES
ACROSS THE REGION...LEADING TO A DECREASE IN SNOW COVERAGE AND
INTENSITY ON TUE. SLIGHT TIMING DIFFERENCES REMAIN WITH THE WAVE
AS THE NAM PRODUCES MORE SNOW THAN THE GFS/GEFS/ECMWF/UKMET
FORECASTS. HIGHER AMOUNTS IN THE BIGHORNS ARE EXPECTED WITH A
LONGER DURATION SNOW.

THE MODELS WERE IN GOOD AGREEMENT ON THE MASS FIELDS WITH THE GFS
INDICATING HIGHER QPF MAXIMA THAT WERE TEMPERED WITH THE MORE
CONSISTENT GEFS MEMBERS...ALONG WITH THE NAM/UKMET/ECMWF QPF AND
TEMPERATURE PROFILES.


NORTHEAST U.S.

A CLOSED LOW IS FORECAST TO DEVELOP ALOFT TONIGHT OVER NORTHERN
NEW YORK AND MOVE SLOWLY EAST
INTO VT AND NH SUNDAY. AS THE LOW MOVES EAST, FALLING HEIGHTS AND
LOWERING FREEZING LEVELS WILL ALLOW PRECIPITATION TO CHANGE OVER
TO SNOW FOR THE NEW YORK ADIRONDACK MOUNTAINS, AND PROBABLY FOR
THE CATSKILL MOUNTAINS AS WELL SUNDAY NIGHT. A FEW INCHES OF
ACCUMULATION ARE LIKELY SUNDAY INTO MONDAY IN THE ADIRONDACKS AS
POST-FRONTAL NORTHWEST WINDS PROVIDE UPSLOPE FLOW OVER WINDWARD
FACING TERRAIN. DECENT AGREEMENT ON THE TIMING OF THE MID-LEVEL
LOW JUSTIFIED A BLEND OF THE ECMWF/GFS/NAM FOR THE THERMAL
PROFILES AND QPF. THE LOW REFORMS OFF THE COAST LATER MON...WITH
WANING PRECIPITATION LOWERING THE SNOW THREAT.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

PETERSEN









$$




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FOUS11 KWBC 300701
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 AM EDT MON APR 30 2018

VALID 12Z MON APR 30 2018 - 12Z THU MAY 3 2018

WITH THE DEPARTURE OF THE HIGHER ELEVATION SNOW ACROSS THE
NORTHEAST U.S. EARLY MONDAY, WINTER WEATHER WILL BE RELEGATED TO
THE INTERMOUNTAIN WEST AND THE ROCKY MOUNTAINS FOR THE BEGINNING
TO MIDDLE OF THE WEEK WITH A LARGE SCALE MID-UPPER LEVEL TROUGH
BECOMING FIRMLY ESTABLISHED OVER THE REGION.

THE FIRST FEATURE OF INTEREST WILL BE AN INVERTED SURFACE TROUGH
AND ACCOMPANYING 700MB LOW DEVELOPING OVER NORTHERN UTAH AND INTO
WYOMING BY THE BEGINNING OF THE DAY 1 PERIOD MONDAY MORNING, AND
THE LAST FEW RUNS OF THE GFS HAVE INDICATED THE GREATEST
REFLECTION OF THIS FEATURE. THE COMBINATION OF STRONG 700MB
FRONTOGENETICAL FORCING, LEFT EXIT JET DYNAMICS, AND BOUNDARY
LAYER UPSLOPE FLOW IS EXPECTED TO RESULT IN SIGNIFICANT LATE
SEASON SNOW FROM THE NORTHERN WASATCH AND UINTA MOUNTAINS OF UTAH,
AND PARTICULARLY THE ABSAROKA, WIND RIVER, AND BIG HORN MOUNTAINS
OF WYOMING. THE POTENTIAL EXISTS FOR ACCUMULATIONS IN EXCESS OF
12 INCHES ABOVE 8000 FEET, AND SOME ENSEMBLE MEMBERS ARE
INDICATING THIS SCENARIO. THE THERMAL PROFILE IS BASED ON A BLEND
OF THE 00Z GFS/NAM AND 12Z ECMWF WITH LOCAL ADJUSTMENTS FOR
TERRAIN.

THE SECOND FEATURE WILL BE A CLOSED LOW THAT IS FORECAST TO
DEVELOP AT THE BASE OF THE TROUGH OVER THE SOUTHWEST US. THE
SHORTWAVE PERTURBATION SHOULD TRACK ROUGHLY PARALLEL TO THE WEST
COAST THROUGH TUESDAY MORNING BEFORE EVOLVING INTO A CLOSED
MID-UPPER LEVEL LOW OVER SOUTHERN NEVADA BY TUESDAY NIGHT.
ENHANCED UPPER LEVEL DIVERGENCE AND BOUNDARY LAYER CONVERGENCE IN
THE VICINITY OF THE LOW-MID LEVEL FRONT IS EXPECTED TO DEVELOP AS
IT CROSSES THE SIERRA NEVADA MOUNTAINS TUESDAY, AND SHOULD
CONTINUE DOWNSTREAM IN TANDEM WITH THE FRONT ACROSS NEVADA AND
THEN THE WASATCH MOUNTAINS. BOTH THE GFS AND ECMWF SHOW 300 MB
DIVERGENCE DEVELOPING IN NORTHERN COLORADO WEDNESDAY AFTERNOON
OWING TO LEFT EXIT JET DYNAMICS, AND THIS WOULD SUPPORT INCREASING
COVERAGE OF SNOW SHOWERS. THE QPF AND THERMAL PROFILES WERE BASED
ON A BLEND OF THE 00Z GFS/NAM AND 12Z ECMWF/EC MEAN.

D. HAMRICK








$$




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FOUS11 KWBC 301943
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 PM EDT MON APR 30 2018

VALID 00Z TUE MAY 01 2018 - 00Z FRI MAY 04 2018

...MOUNTAIN RANGES OF COLORADO...UTAH AND WYOMING...

A CLOSED UPPER LEVEL LOW OVER THE INTERMOUNTAIN WEST WAS IN THE
PROCESS OF OPENING INTO A TROUGH WITH SEVERAL +PV ANOMALIES
CONTINUING TO ROTATE ACROSS THE REGION. ONE PROMINENT PV ANOMALY
WAS LIFTING NORTHEAST FROM UTAH INTO WYOMING...AND IS PROVIDING
THE FOCUS FOR SOME HEAVY PRECIPITATION THAT WILL CONTINUE INTO THE
DAY 1 FORECAST PERIOD (TONIGHT AND TUESDAY). SOME LIGHTNING WAS
EVEN NOTED IN PARTS OF SOUTHWEST WYOMING THIS AFTERNOON JUST AHEAD
OF THE PV ANOMALY...AND WITH SOME CONVECTIVE PRECIP THE LOCALIZED
RATES COULD BE RELATIVELY HIGH. SNOW APPEARS LIKELY AT HIGHER
ELEVATIONS IN WYOMING THROUGH TONIGHT...BUT SHOULD BEGIN TAPERING
OFF DURING THE DAY ON TUESDAY.

PRECIPITATION IN THE WEST ON DAYS 2 AND 3 (TUESDAY NIGHT THROUGH
THURSDAY) WILL BE THE RESULT OF ANOTHER SHORTWAVE...SHARPLY
DIGGING INTO THE WEST COAST OVER THE NEXT 24 HOURS AND REINFORCING
THE LARGE SCALE TROUGH OVER THE WEST. ASSOCIATED DCVA AND
FAVORABLY ALIGNED LEFT EXIT REGION OF AN UPPER LEVEL JET STREAK
SHOULD FOCUS THE HEAVIEST PRECIPITATION FROM UTAH INTO SOUTHWEST
COLORADO ON DAY 2...AND THEN INTO NORTHERN AND EASTERN COLORADO ON
DAY 3.

THROUGH MUCH OF THE PERIOD...SNOW LEVELS APPEAR TO BE AT LEAST
7000-8000 FEET IN MOST LOCATIONS (EXCEPT PERHAPS WYOMING WHERE
THEY COULD BE A LITTLE LOWER). THIS SHOULD RESTRICT HEAVY SNOW TO
THE HIGHEST ELEVATION OF COLORADO...UTAH AND WYOMING. WPC WWD 50
PERCENT OR GREATER PROBABILITIES OF AT LEAST 8 INCHES OF SNOW BY
THURSDAY ARE ALMOST EXCLUSIVELY RESTRICTED TO ELEVATION OF 8000
FEET OR HIGHER IN THIS REGION.

THE MOST FAVORABLE ALIGNMENT OF SYNOPTIC FEATURES AND SUFFICIENTLY
HIGH TERRAIN APPEARS TO BE IN PORTIONS OF NORTHEAST COLORADO FROM
WEDNESDAY EVENING INTO THURSDAY MORNING...PARTICULARLY IN THE
MEDICINE BOW MOUNTAINS AND INTO THE VICINITY OF ROCKY MOUNTAIN
NATIONAL PARK. AS THE PV ANOMALY KICKS THROUGH THE DESERT
SOUTHWEST AND BEGINS TO EJECT TOWARD THE CENTRAL HIGH PLAINS...A
LOW-LEVEL CYCLONE SHOULD DEVELOP NEAR THE CO-KS BORDER WITH A
MID-LEVEL DEFORMATION ZONE FOCUSING TO THE NORTHWEST IN PART OF NE
CO. ADDITIONALLY...THE LEFT EXIT REGION OF AN UPPER LEVEL JET
STREAK (AND ENHANCED UPPER LEVEL DIVERGENCE) WILL BE SITUATED OVER
NE CO AS WELL. THE 12-18 HOUR PERSISTENCE OF STRONG SUPPORT FOR
VERTICAL MOTION SHOULD LEAD TO A PERIOD OF HEAVY SNOW IN THE
AFOREMENTIONED AREAS. IT IS THESE RANGES IN NE CO WHERE WPC WWD
PROBABILITIES OF 18+ INCHES OF SNOW ARE IN EXCESS OF 50 PERCENT.


THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

LAMERS

$$




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FOUS11 KWBC 011919
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
319 PM EDT TUE MAY 01 2018

VALID 00Z WED MAY 02 2018 - 00Z SAT MAY 05 2018


DAYS 1 THROUGH 3...


...GREAT BASIN/CENTRAL AND SOUTHERN ROCKIES/SOUTHWEST...

A POSITIVELY TILTED LONG WAVE TROUGH EXTENDING FROM THE NORTHERN
ROCKIES INTO SOUTHERN CA ON DAY 1 BRIEFLY CLOSES OFF IN THE MID
LEVELS OVER THE GREAT BASIN LATE ON DAY 1 INTO DAY 2. THE LONG
WAVE TROUGH THEN EXITS INTO THE NORTHERN AND CENTRAL PLAINS DURING
DAY 3. UPSLOPE FLOW ASSOCIATED WITH DEVELOPING LOW PRESSURE OVER
SOUTHEAST CO...COMBINED WITH LIFT WITH THE MID LEVEL SYSTEM...IS
EXPECTED TO PRODUCE HEAVY SNOWFALL OVER PORTIONS OF THE WASATCH
RANGE IN UT...AS WELL AS THE CENTRAL AND SOUTHERN ROCKIES. THERE
WAS GOOD MODEL AGREEMENT WITH THE TIMING AND PLACEMENT OF THE
SYNOPTIC SCALE FEATURES...SO THE THERMAL PORTION OF THE FORECAST
WAS BASED ON A MULTI MODEL BLEND. THE QPF PORTION OF THE FORECAST
WAS BASED ON THE MOST RECENT WPC QPF.

DAY 1...
AS A POSITIVELY TILTED LONG WAVE TROUGH CROSSES THE GREAT BASIN
AND CENTRAL AND SOUTHERN ROCKIES DURING DAY 1...LIFT ASSOCIATED
WITH THE MID LEVEL SYSTEM AIDS IN SPINNING UP SURFACE LOW PRESSURE
ON A LOW LEVEL BAROCLINIC ZONE EXTENDING ACROSS CENTRAL AND
SOUTHEAST CO. AS THE LOW LEVEL CIRCULATION BECOMES BETTER
ORGANIZED...THE UPSLOPE COMPONENT TO THE LOW LEVEL FLOW BECOMES
FOCUSED ON THE SAN JUAN RANGE IN SOUTHWEST CO. THERE WAS A MULTI
MODEL SIGNAL FOR 12+ INCHES OF SNOWFALL ACROSS THE HIGHER TERRAIN
(WHERE SNOW LEVELS EVENTUALLY DROP TO BELOW 10000 FEET)...WITH THE
12Z NAM AND 09Z SREF SHOWING 12+ INCH AMOUNTS.
INTERESTINGLY...NONE OF THE MEMBERS OF THE MOST RECENT ECMWF
ENSEMBLE OUTPUT SHOWED 12+ INCHES OF SNOWFALL HERE.

FURTHER WEST ACROSS THE WASATCH AND UINTA MOUNTAINS IN UT...SNOW
LEVELS DROP BELOW 8000 FEET. THERE SHOULD BE SUFFICIENT MOISTURE
IN THE UPSLOPE FLOW TO SUPPORT LOCAL 4 TO 8 INCHES SNOWFALL
AMOUNTS ABOVE THIS LEVEL. THESE AMOUNTS WERE SUPPORTED BY MEMBERS
OF BOTH THE 09Z SREF AND THE MOST RECENT ECMWF ENSEMBLE OUTPUT
SHOWING THE POTENTIAL FOR 8+ INCHES OF SNOW OVER THE HIGHER
TERRAIN OF EACH RANGE.

FINALLY...SNOW LEVELS ACROSS THE MOGOLLON RIM IN AZ FALL BELOW
8000 FEET WITH THE APPROACH OF THE MID LEVEL SYSTEM. THE FALLING
SNOW LEVELS SUPPORT LOCAL 3 TO 6 INCH SNOWFALL AMOUNTS ACROSS THE
NORTHERN PORTION OF THE RIM...WITH LESSER AMOUNTS FURTHER
SOUTHEAST.

DAY 2...
THE SURFACE LOW FORMING OVER SOUTHEAST CO DEEPENS AS IT TREKS
ACROSS KS DURING DAY 2...REACHING NORTHEAST KS BY THE END OF THE
PERIOD. AS THE SURFACE LOW BECOMES BETTER ORGANIZED...THE LOW
LEVEL UPSLOPE FLOW FOCUSES 0.50 INCH PRECIPITABLE WATER AIR ON THE
CENTRAL AND NORTHERN FRONT RANGE IN CO AND PORTIONS OF SOUTHEAST
WY. SNOW LEVELS ARE EXPECTED TO FALL TO NEAR 8000 FEET AS THE BEST
MID LEVEL LIFT CROSSES THE REGION (GENERALLY BETWEEN 03/00Z AND
03/06Z). THE COMBINATION OF MOISTURE IN THE UPSLOPE FLOW AND
MARGINAL INSTABILITY IN THE COLUMN (DUE AT LEAST IN PART TO
STEEPENING LAPSE RATES) IS EXPECTED TO PRODUCE AN AREA OF 12 TO 18
INCHES OF SNOWFALL...CENTERED ON THE NORTHERN CO FRONT RANGE.
THESE AMOUNTS ARE WELL SUPPORTED BY OPERATIONAL 12Z MODELS (SUCH
AS THE 12Z NAM/00Z ECMWF)...AS WELL AS MEMBERS OF THE MOST RECENT
ECMWF ENSEMBLE OUTPUT. IN FACT...BOTH THE 12Z NAM/00Z ECMWF
INDICATED THE POTENTIAL FOR AS MUCH AS 20 INCHES OF SNOWFALL...AND
THESE AMOUNTS COULD BE THE MAXIMUM AMOUNTS ABOVE 8000 FEET IN THIS
REGION.

RESIDUAL MOISTURE AND UPSLOPE FLOW ACROSS THE WASATCH AND UINTA
RANGES IN UT SHOULD BE ENOUGH TO PRODUCE LOCAL 3 TO 6 INCH
SNOWFALL AMOUNTS ABOVE 7000 FEET.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

HAYES

$$




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FOUS11 KWBC 020618
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
217 AM EDT WED MAY 2 2018

VALID 12Z WED MAY 2 2018 - 12Z SAT MAY 5 2018


DAYS 1 THROUGH 3...

THE FORECAST PERIOD WILL BEGIN ON WEDNESDAY MORNING WITH A
VERTICALLY STACKED CLOSED LOW CENTERED OVER THE LAS VEGAS AREA
THAT IS EXPECTED TO EVOLVE INTO A POSITIVELY TILTED LONG WAVE
TROUGH BY THURSDAY MORNING. THIS WILL PLACE THE MOUNTAINS OF
EASTERN UTAH AND CENTRAL COLORADO UNDER THE FAVORABLE LEFT EXIT
REGION OF THE UPPER LEVEL JET. THIS TROUGH AXIS THEN EXITS ACROSS
THE NORTHERN AND CENTRAL PLAINS BY THURSDAY NIGHT AND FORCING FOR
ASCENT WANES BY THE END OF DAY 2 OVER THIS REGION. SURFACE
CYCLOGENESIS IS FORECAST TO ENSUE OWING TO DIVERGENCE ALOFT FROM
THE UPPER TROUGH OVER EASTERN COLORADO, AND STEADY UPSLOPE FLOW IN
THE BOUNDARY LAYER NORTH OF THE SURFACE LOW WILL ADVECT LOW LEVEL
MOISTURE TOWARDS THE FRONT RANGE.

MODERATE TO HEAVY SNOWFALL IS EXPECTED FOR PORTIONS OF THE WASATCH
AND UINTA RANGES IN UTAH, AND ALSO THE SAN JUAN MOUNTAINS AND
NORTH CENTRAL COLORADO/SOUTH CENTRAL WYOMING ROCKIES AS FREEZING
LEVELS LOWER BEHIND THE FRONT. THE COMBINATION OF MOISTURE IN THE
UPSLOPE FLOW AND MARGINAL INSTABILITY OWING TO STEEPENING LAPSE
RATES IS EXPECTED TO PRODUCE A MAXIMUM AREA OF 8 TO 12 INCHES OF
SNOWFALL, PRIMARILY CENTERED ON THE NORTHERN COLORADO FRONT RANGE.
THERE WAS GOOD MODEL AGREEMENT WITH THE TIMING AND PLACEMENT OF
THE SYNOPTIC SCALE FEATURES, SO THE THERMAL PORTION OF THE
FORECAST WAS BASED ON A BLEND OF THE 00Z GFS/NAM AND 12Z ECMWF.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT
NATIONWIDE.

D. HAMRICK

$$




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FOUS11 KWBC 021927
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
326 PM EDT WED MAY 02 2018

VALID 00Z THU MAY 03 2018 - 00Z SUN MAY 06 2018


DAYS 1 AND 2...


...GREAT BASIN/CENTRAL AND SOUTHERN ROCKIES...

A BROAD LONG WAVE TROUGH CROSSES THE CENTRAL AND SOUTHERN ROCKIES
DURING DAY 1...BEFORE WEAKENING AND EXITING INTO THE PLAINS DURING
DAY 2. SURFACE LOW PRESSURE FORMING IN RESPONSE TO THE MID LEVEL
SYSTEM TRACKS FROM SOUTHEAST CO INTO THE MID MS VALLEY...AND THE
UPSLOPE FLOW ASSOCIATED WITH THE SURFACE LOW TRANSPORTS MOISTURE
FROM THE PLAINS FOR HEAVY SNOWFALL ACROSS THE NORTHERN FRONT RANGE
IN CO INTO SOUTHEAST WY. THERE WAS GENERALLY GOOD MODEL AGREEMENT
WITH THE SYNOPTIC SETUP...SO THE THERMAL PORTION OF THE FORECAST
WAS BASED ON A MULTI MODEL BLEND. THE QPF PORTION OF THE FORECAST
WAS BASED ON THE MOST RECENT WPC QPF.

DAY 1...
LIFT ASSOCIATED WITH A BROAD POSITIVELY TILTED LONG WAVE TROUGH
MOVING ACROSS THE CENTRAL AND SOUTHERN ROCKIES DURING DAY 1 AIDS
IN SPINNING UP SURFACE LOW PRESSURE OVER SOUTHEAST CO ON A LOW
LEVEL BAROCLINIC ZONE BISECTING THE STATE. AS THE LOW BECOMES
BETTER ORGANIZED AND CROSSES WESTERN KS DURING THE FIRST PART OF
THE PERIOD... INCREASING UPSLOPE FLOW TRANSPORTS 0.50/0.75 INCH
PRECIPITABLE WATER AIR ACROSS PORTIONS OF NORTHEAST CO AND
SOUTHEAST WY...WHICH PEAKS BEFORE 03/12Z. SNOW LEVELS DROP WITH
THE APPROACH OF THE MID LEVEL SYSTEM...BOTTOMING OUT BETWEEN
8000/9000 FEET (BASED ON THE MOST RECENT NBM) OVER NORTHEAST CO
AND SOUTHEAST WY DURING THE PERIOD OF BEST SYNOPTIC SCALE ASCENT.

THE BEST LIFT ASSOCIATED WITH THE MID LEVEL SYSTEM ALSO PEAKS
DURING THIS TIME...AND THE COMBINATION OF SYNOPTIC SCALE ASCENT
AND UPSLOPE FLOW IS EXPECTED TO PRODUCE AN AREA OF 8 TO 12 INCHES
OF SNOWFALL ALONG THE NORTHERN FRONT RANGE OF CO. THESE VALUES ARE
SUPPORTED BY MEMBERS OF THE MOST RECENT ECMWF ENSEMBLE OUTPUT...AS
WELL AS A FEW 12Z MODEL SOLUTIONS (SUCH AS THE 12Z NAM/12Z GFS AND
12Z HREF MEAN). IN FACT...BOTH THE 12Z NAM/09Z SREF SUGGEST THAT
LOCAL 20 INCH SNOWFALL AMOUNTS ARE POSSIBLE OVER THE NORTHERN CO
FRONT RANGE...BUT CONSIDERING THE BEST MOISTURE AND INSTABILITY
ARE EXPECTED OVER FAR WESTERN NE...THESE VALUES MAY BE OUT OF
REACH.

FURTHER SOUTH AND WEST...THE MOISTURE PLUME IS NOT AS
IMPRESSIVE...BUT THERE SHOULD SUFFICIENT SYNOPTIC SCALE LIFT AND
UPSLOPE FLOW TO PRODUCE LOCAL 3 TO 6 INCH SNOWFALL AMOUNTS OVER
THE HIGHER TERRAIN OF THE UINTA MOUNTAINS IN UT...AS WELL AS THE
SAN JUAN RANGE IN CO.

DAY 2...
THE SURFACE AND MID LEVEL SYSTEMS PULL OUT OF THE ROCKIES DURING
DAY 2...AND LOW AND MID LEVEL WINDS SHIFT TO THE WEST NORTHWEST.
THE MOISTURE PLUME FROM THE CENTRAL PLAINS EXITS AS WELL...BUT
THERE SHOULD BE ENOUGH MOISTURE AND LIFT TO PRODUCE LOCAL 3 INCH
SNOWFALL AMOUNTS OVER THE SAN JUAN MOUNTAINS IN CO AND NEARBY
NORTHERN NM.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


HAYES


THIS IS THE LAST SCHEDULED DISCUSSION BETWEEN NOW AND SEPTEMBER
15TH. UNSCHEDULED DISCUSSIONS ARE POSSIBLE AS EVENTS WARRANT.

$$




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------------=_1538036198-1955-3482
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FOUS11 KWBC 270816
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Thu Sep 27 2018

Valid 12Z Thu Sep 27 2018 - 12Z Sun Sep 30 2018


DAY 1...

...Northern Rockies/High Plains...
Models show shortwave energy embedded within northwest flow
sliding out of western Canada across the northern Rockies and High
Plains on Thursday. Low to mid level frontogenesis along with
upslope flow is expected to support precipitation across the
region, with decreasing snow levels as colder air moves into the
region Thursday night. Accumulating snows are expected along the
higher elevations of the northern Rockies from northwest Montana
to north-central Wyoming. Heaviest amounts are expected to fall
along the Big Horns, with WPC Day 1 probabilities (ending 12 UTC
Fri) indicating a Slight Risk for accumulations of 8-inches or
more. Accumulating snows are also possible further east across
the higher elevations of the Black Hills.

The probability of significant icing is less than 10 percent.

DAY 2...

The probability of significant icing and/or snow is less than 10
percent.

DAY 3...

...Northern Rockies...
Mainly dry conditions are expected late Friday into early
Saturday, with precipitation returning to portions of the northern
Rockies around midday ahead of a shortwave trough digging through
western Canada. Increasing upslope flow with low to mid level
frontogenesis, along with a reinforcing shot of cold air will
support another round of precipitation with decreasing snow levels
Saturday into early Sunday. Heaviest snow accumulations are
expected to center along the higher elevations of the Lewis Range
in northwest Montana, with WPC Day 3 probabilities (ending 12 UTC
Sun) indicate a Moderate Risk for accumulations of 8-inches or
more.

The probability of significant icing is less than 10 percent.

Pereira

$$




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FOUS11 KWBC 272019
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Thu Sep 27 2018

Valid 00Z Fri Sep 28 2018 - 00Z Mon Oct 01 2018


DAY 1...

...Northern Rockies/High Plains...
Models show shortwave energy embedded within northwest flow with a
300 mb jet axis extending northwest to southeast across MT and
east across SD tonight. Upper level divergence maxima in the
right jet entrance will combine with low to mid level
frontogenesis along with upslope flow to produce precipitation
across the region, with decreasing snow levels as colder air moves
into the region tonight. The heaviest amounts are expected to
fall along the WY Big Horns, with WPC Day 1 probabilities (ending
12 UTC Fri) indicating a Slight Risk for accumulations of 8-inches
or more. Several inches are expected further east across the
higher elevations of the Black Hills of SD.

The probability of significant icing is less than 10 percent.

DAY 2...

A relative lull in precipitation occurs as the upper jet weakens,
along with the strength of low level convergence within the
frontal zone. Light snows may occurs in the mountains of
northwest MT, with a few inches of snow accumulation expected.

The probability of significant icing and/or snow is less than 10
percent.

DAY 3...

...Northern Rockies...
Precipitation returning to portions of the northern Rockies around
midday ahead of a shortwave trough digging through western Canada.
Increasing upslope flow with low to mid level frontogenesis, with
the 12z nam/gfs showing 700 mb warm/moist advection over the top
of the low level cold air, will support another round of
precipitation with decreasing snow levels Saturday into early
Sunday. Heaviest snow accumulations are expected to center along
the front range in northwest Montana and Glacier National Park,
with WPC Day 3 probabilities for Sat night-Sunday indicating a
Moderate Risk for accumulations of 8-inches or more.

The probability of significant icing is less than 10 percent.

Petersen


$$




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FOUS11 KWBC 272020
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
420 PM EDT Thu Sep 27 2018

Valid 00Z Fri Sep 28 2018 - 00Z Mon Oct 01 2018


DAY 1...

...Northern Rockies/High Plains...
Models show shortwave energy embedded within northwest flow with a
300 mb jet axis extending northwest to southeast across MT and
east across SD tonight. Upper level divergence maxima in the
right jet entrance will combine with low to mid level
frontogenesis along with upslope flow to produce precipitation
across the region, with decreasing snow levels as colder air moves
into the region tonight. The heaviest amounts are expected to
fall along the WY Big Horns, with WPC Day 1 probabilities (ending
12 UTC Fri) indicating a Slight Risk for accumulations of 8-inches
or more. Several inches are expected further east across the
higher elevations of the Black Hills of SD.

The probability of significant icing is less than 10 percent.

DAY 2...

A relative lull in precipitation occurs as the upper jet weakens,
along with the strength of low level convergence within the
frontal zone. Light snows may occurs in the mountains of
northwest MT, with a few inches of snow accumulation expected.

The probability of significant icing and/or snow is less than 10
percent.

DAY 3...

...Northern Rockies...
Precipitation returning to portions of the northern Rockies around
midday ahead of a shortwave trough digging through western Canada.
Increasing upslope flow with low to mid level frontogenesis, with
the 12z nam/gfs showing 700 mb warm/moist advection over the top
of the low level cold air, will support another round of
precipitation with decreasing snow levels Saturday into early
Sunday. Heaviest snow accumulations are expected to center along
the front range in northwest Montana and Glacier National Park,
with WPC Day 3 probabilities for Sat night-Sunday indicating a
Slight Risk for accumulations of 8-inches or more.

The probability of significant icing is less than 10 percent.

Petersen


$$




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FOUS11 KWBC 280805
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Fri Sep 28 2018

Valid 12Z Fri Sep 28 2018 - 12Z Mon Oct 01 2018


Day 1...

The probability of significant icing and/or snow is less than 10
percent.

Days 2/3...

...Northern Rockies and High Plains...
Greatest potential for significant snow accumulations is expected
to occur Saturday into early Sunday and focus mainly across the
mountains of northwest Montana. Precipitation is forecast to
redevelop across the region as a northern stream shortwave trough
moves across western Canada, while a weakening Pacific low
approaches from the west. Low to mid level frontogenesis and
easterly flow will raise the potential for precipitation east of
the Divide while a reinforcing shot of colder air brings snow
levels down late Saturday into early Sun. WPC probabilities
continue to signal the potential for significant accumulations
along the Lewis Range, showing a Slight Risk for accumulations of
8-inches or more during the Day 2 period (ending 12 UTC Sun).
Precipitation is expected to continue into the Day 3 period and
spread east producing some light snow accumulations out into the
High Plains, with additional accumulations across the mountains as
well. However, snow levels are expected to rise ahead of the
approaching Pacific wave, limiting the threat for any additional
significant amounts. Then by early Monday, precipitation is
expected to wane as the Pacific system moves east.

The probability of significant icing is less than 10 percent.

Pereira



$$




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FOUS11 KWBC 281950
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Fri Sep 28 2018

Valid 00Z Sat Sep 29 2018 - 00Z Tue Oct 02 2018



Days 1/2/3...

...Northern Rockies and High Plains...

Greatest potential for significant snow accumulations is expected
to occur Saturday into early Sunday and focus mainly across the
mountains of northwest Montana, with accumulating snow in several
other ranges. Precipitation is forecast to redevelop across the
region as low to mid level frontogenesis and easterly flow will
enhance precipitation east of the Divide while a reinforcing shot
of colder air brings snow levels down late Saturday into early
Sun. Snow in the mountains commences Sat with 700 mb convergence
combining with the low level frontal circulation to generate lift.

WPC probabilities continue to signal the potential for significant accumulations along the Lewis Range and Glacier National Park,
showing a Slight Risk for accumulations of 8-inches or more during
the Day 2 period. The models are converging the forecast areas
impacted by the event, so equal weighting was given to each
solution.

Precipitation is expected to wane on day 3 (Monday) as the 500 mb
wave deamplifies in the model forecasts as it crosses the northern
Plains. The reduced magnitude of low level frontogenesis and
convergence leads to the accumulations being a couple of inches in
parts of western ND and northeast MT.

The probability of significant icing is less than 10 percent days
1-3.

Petersen



$$




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FOUS11 KWBC 290806
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EDT Sat Sep 29 2018

Valid 12Z Sat Sep 29 2018 - 12Z Tue Oct 02 2018


Days 1/2...

...Northern Rockies/High Plains...
Shortwave energy dropping into the base of broad upper trough will
help drive colder air across the northern Rockies and High Plains
on Saturday. Increasing low to mid level frontogenesis and
upslope flow will support an increasing chance for precipitation
across central and western Montana, with snow levels decreasing as
colder air filters in across the region. Overnight guidance
continues to show the heaviest snow accumulations falling east of
the Divide, centering along the Lewis Range in northwest Montana,
where WPC probabilities show at least a Slight Risk for
accumulations of 8-inches or more during the Day 1 period (ending
12 UTC Sunday). As a weakening Pacific mid-upper level low moves
into the Northwest, precipitation is expected to spread further
east across central into eastern Montana and western North Dakota
late Saturday into Sunday. Some light snow accumulations are
possible across portions of central into eastern Montana and
western North Dakota, however marginal boundary layer temperatures
at the onset and subsequent warming is expected to hamper the
potential for significant amounts. As the Pacific system moves
east and a shortwave ridge begins to build, drier conditions can
be expected across much of the region on Monday.

The probability of significant icing is less than 10 percent.

Day 3...

The probability of significant icing and/or snow is less than 10
percent.

Pereira


$$




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FOUS11 KWBC 291932
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Sat Sep 29 2018

Valid 00Z Sun Sep 30 2018 - 00Z Wed Oct 03 2018


Days 1/2...

...Northern Rockies/High Plains...
Increasing low to mid level frontogenesis and upslope flow will
combine with upper divergence maxima ahead of a closed low to
support precipitation across central and western Montana, with
snow levels decreasing as colder air filters in across the region.


Guidance continues to show the heaviest snow accumulations falling
east of the Divide, centering along the Lewis Range/Glacier
National Park in northwest Montana. WPC probabilities show at
least a Slight Risk for accumulations of 8 inches or more during
the Day 1 period.

The upper level low is forecast to weaken steadily Sunday night
into Monday. Downstream from the deamplifying wave,
light precipitation is expected to spread further east across
central into eastern Montana and western North Dakota late
Saturday into Sunday. Some light snow accumulations are possible
across portions of central into eastern Montana and western North
Dakota, however marginal boundary layer temperatures and light
liquid precipitation amounts are expected to hamper the potential
for significant snow amounts.

As the wave departs further east and a shortwave ridge begins to
build, drier conditions can be expected across much of the
northern Plains on Monday.

The probability of significant icing is less than 10 percent.

Day 3...

The probability of significant snow and/or icing is less than 10
percent.

Petersen





$$




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FOUS11 KWBC 291944
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Sat Sep 29 2018

Valid 00Z Sun Sep 30 2018 - 00Z Wed Oct 03 2018


Days 1/2...

...Northern Rockies/High Plains...
Increasing low to mid level frontogenesis and upslope flow will
combine with upper divergence maxima ahead of a closed low to
support precipitation across central and western Montana, with
snow levels decreasing as colder air filters in across the region.


Guidance continues to show the heaviest snow accumulations falling
east of the Divide, centering along the Lewis Range/Glacier
National Park in northwest Montana. WPC probabilities show at
least a Slight Risk for accumulations of 8 inches or more during
the Day 1 period.

The upper level low is forecast to weaken steadily Sunday night
into Monday. Downstream from the deamplifying wave,
light precipitation is expected to spread further east across
central into eastern Montana and western North Dakota late
Saturday into Sunday. Some light snow accumulations are possible
across portions of central into eastern Montana and western North
Dakota, however marginal boundary layer temperatures and light
liquid precipitation amounts are expected to hamper the potential
for significant snow amounts.

As the wave departs further east and a shortwave ridge begins to
build, drier conditions can be expected across much of the
northern Plains on Monday.

The probability of significant icing is less than 10 percent.

Day 3...

The models show heights beginning to lower again as an upper level
trough builds into the Pacific Northwest Tue. Gradual cooling
aloft opens up the possibility of snow developing in the higher
elevations of the the WA Cascades and also the northern Rockies.
A minority of solutions indicate up to four inches of snow in
Glacier National Park, MT, but most solutions have low QPF in the
form of snow, so just a low risk of four inches is shown.

The probability of significant icing is less than 10 percent.

Petersen





$$




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------------=_1538294410-1955-4891
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FOUS11 KWBC 300800
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Sun Sep 30 2018

Valid 12Z Sun Sep 30 2018 - 12Z Wed Oct 03 2018


Days 1-3...

...Northern Rockies and High Plains...
Mixed precipitation, resulting in some light snow accumulations is
expected to continue this morning across portions Montana,
northern Wyoming and western North Dakota. Warming conditions
after 12z should limit the potential for any widespread
significant amounts on Sunday. Any significant snowfall threat is
forecast to remain north of the Canadian border on Monday into
early Tuesday. However, heavy snows may extend south along the
Canadian Rockies into northwest Montana as a well-defined
shortwave trough digs southwest across western Canada into the
northwestern U.S. Tuesday night into Wednesday morning. WPC Day 3 probabilities (ending 12 UTC Wed) indicate a Slight Risk for
accumulations of a foot or more in the higher elevations of the
northern sections of Glacier National Park.

The probability of significant icing is less than 10 percent.

Pereira

$$




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FOUS11 KWBC 302003
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
402 PM EDT Sun Sep 30 2018

Valid 00Z Mon Oct 01 2018 - 00Z Thu Oct 04 2018


Days 1-3...

...Northern Rockies and High Plains...
Mixed precipitation, resulting in some light snow accumulations,
is expected to continue this evening across portions of eastern
Montana and western North Dakota. With the warm front lifting
north, any significant snowfall threat is forecast to remain north
of the Canadian border on Monday into early Tuesday.

However, heavy snows may extend south along the Canadian Rockies
into northwest Montana as a well-defined shortwave trough digs
southwest across western Canada into the northwestern U.S. Tuesday
night into Wednesday morning. Falling heights lead to decreasing
snow levels, so rain should change to snow at higher elevations
first.
There are timing differences as to how soon snow develops in the
Rocky Mountain front/Glacier National Park, resulting in a
differences in several inches of snow among various model
solutions. The 700 mb low opens up into a wave and moves steadily
east out of the northern Rockies and across the northern plains,
with succeeding drying and loss of ascent leading to decreasing coverage/amounts on Wed.

Combined Day 2 plus Day 3 snow amounts show potential for
accumulations of a foot or more in the higher elevations of the
northern sections of Glacier National Park.

The probability of significant icing is less than 10 percent Days
1-3.

Petersen


$$




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FOUS11 KWBC 010828
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Mon Oct 01 2018

Valid 12Z Mon Oct 01 2018 - 12Z Thu Oct 04 2018


Day 1...

The probability of significant icing and/or snow is less than 10
percent.

Day 2...

...Northern Rockies...
Models continue to show a well-defined shortwave trough digging
south through British Columbia on Tuesday before pivoting
southeast across the Pacific Northwest into the northern Rockies
late Tuesday into early Wednesday. This will bring the threat for
heavy snow south along the Canadian Rockies into northwest Montana
by Tuesday night, with models continuing to signal the potential
for heavy accumulations by Wednesday morning across portions of
Glacier National Park. WPC Day 2 probabilities (ending 12 UTC
Wed) show a moderate risk for accumulations of a foot or more
across the higher elevations within the northern portion of the
park.

The probability of significant icing is less than 10 percent.

Day 3...

...Sierra...
An upper low dropping south along the California coast on Tuesday
into early Wednesday is expected to move inland Wednesday night -
producing some high elevation snow across the Sierra. WPC
probabilities show some chance for accumulations of 4 inches or
more, mainly for elevations above 9000 ft.

The probability of significant icing is less than 10 percent.

Pereira


$$




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FOUS11 KWBC 011930
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Mon Oct 01 2018

Valid 00Z Tue Oct 02 2018 - 00Z Fri Oct 05 2018


Days 1/2...

...Northern Rockies...
Models continue to show a well-defined shortwave trough digging
south through British Columbia on Tuesday before pivoting
southeast across the Pacific Northwest into the northern Rockies
late Tuesday into early Wednesday. North of the low track, strong
low level frontogenesis and cooling temperatures will bring the
threat for heavy snow south along the Rocky Mountain front/Glacier
National Park in northwest Montana Tuesday to Wednesday, with
models continuing to signal the potential for heavy accumulations
around a foot in higher elevations. The higher probabilities are
focused on Tuesday and subside eon Wednesday. The models cluster
well so no solution was given more weighting than other model
runs.

The probability of significant icing is less than 10 percent.

Day 3...

...Sierra...
An upper low dropping south along the California coast on Tuesday
and Wednesday is expected to move inland Wednesday night, with the
arrival of the low resulting in enhanced moisture and lift
crossing the ranges of CA. High elevation snow is expected across
the Sierra Nevada range. The event concludes Thu as the 700 mb
trough moves further inland, followed by weakening lift and drier
air aloft resulting in reduced coverage/intensity of snow showers.
WPC probabilities show some chance for accumulations of 4 inches
or more, mainly for elevations above 9500 ft.

The probability of significant icing is less than 10 percent Days
1-3.

Petersen


$$




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FOUS11 KWBC 020811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Tue Oct 02 2018

Valid 12Z Tue Oct 02 2018 - 12Z Fri Oct 05 2018


Day 1...

...Northern Rockies...
As a well-defined shortwave trough digging south through British
Columbia pivots east across the Pacific Northwest and northern
Rockies, there remains a good model signal for heavy snows
extending south from the Canadian into the far northern U.S.
Rockies Tuesday into early Wednesday. Supported by low level northerly-northeasterly winds, heaviest amounts are expected to
fall across the higher elevations of northern Glacier National
Park, where WPC probabilities continue to indicate a moderate risk
for accumulations of a foot or more by 12 UTC Wednesday.

The probability of significant icing is less than 10 percent.

Day 2...

...Northern Plains...
The previously noted shortwave is forecast to move progressively
east, with precipitation waning across the northern Rockies after
12 UTC Wednesday. Precipitation moving east across the northern
High Plains, will include mixed precipitation with some light snow accumulations possible along the U.S./Canada border from
northeastern Montana into northwestern North Dakota.

...Sierra...
An upper low dropping south along the California coast on
Wednesday is forecast to move inland overnight, producing some
high elevation snows over the Sierra. WPC probabilities continue
to indicate the potential for accumulating snows for elevations
above 9000 ft.

The probability of significant icing is less than 10 percent.

DAY 3...

...Northern Rockies...
Models show a shortwave trough digging southeast across the
Pacific Northwest into the northern Rockies late Thursday into
early Friday. This is forecast to result in mountain snows from
western Montana and central Idaho to perhaps as far south as
northern Utah. Greater threat for heavier amounts is across the
southwestern Montana and northwestern Wyoming ranges, with WPC
probabilities indicating a Slight Risk for localized amounts of
8-inches or more.

The probability of significant icing is less than 10 percent.

Pereira

$$




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FOUS11 KWBC 022030
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
429 PM EDT Tue Oct 02 2018

Valid 00Z Wed Oct 03 2018 - 00Z Sat Oct 06 2018


Day 1...

...Northern Rockies across the Central US/Canada border...
A potent shortwave will race eastward from Washington spawning
surface cyclogenesis. There is good model consensus in snow along
the border from Montana into North Dakota through through
Wednesday as warm advection aloft drives strong lift. Upslope
enhancement on low-level northeasterly winds is expected to
produce the heaviest amounts in the higher terrain of the northern
Rockies including Glacier National Park, where high probabilities
for up to 1 foot of snow exist by 00 UTC Thursday. The probability
for 4 inches of snow decreases significantly from northeastern
Montana into northern North Dakota.

The probability of significant icing is less than 10 percent.

Day 2...

Return flow developing around high pressure moving into the
Central Plains will increase moisture into the Rockies while a
filling shortwave ejects northeast from southern California.
Temperatures will be generally too warm for snow except in the
highest elevation above 9000 ft in the southern Bitterroot range
as well as the Uinta Mountains.

The probability of significant icing is less than 10 percent.

DAY 3...

...Northern Rockies...
A trough diving from the Pacific Northwest will spawn weak low
pressure which will drop southeast into the northern plains before
dissipating Friday night as it gets absorbed into a more
significant low in the lee of the Rockies. This will result in
mountain snows across the central and northern Rockies. The
highest amounts are likely in the higher terrain of southern
Montana into northwest Wyoming where moderate probabilities exist
for 4 to 8 inches of snow.

The probability of significant icing is less than 10 percent.

Weiss

$$




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FOUS11 KWBC 030813
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 AM EDT Wed Oct 03 2018

Valid 12Z Wed Oct 03 2018 - 12Z Sat Oct 06 2018

Day 1...
...Northern Plains...
A shortwave trough currently impacting the northern Rockies and
High Plains is forecast to move progressively east, with
precipitation waning across the northern Rockies Wednesday
morning. Precipitation moving east across the northern High
Plains, will include mixed precipitation with some light snow
accumulations possible along the international border from
northeastern Montana into northern North Dakota. WPC Day 1
probabilities indicate a Slight Risk for accumulations of 4-inches
or more across this area.

...Sierra...
An upper low dropping south along the California coast on
Wednesday is forecast to move inland overnight, producing some
high elevation snows over the Sierra. WPC probabilities continue
to indicate the potential for accumulating snows for elevations
above 9000 ft.

The probability of significant icing is less than 10 percent.

Day 2...

...Northern Rockies...
Models show a shortwave trough digging southeast across the
Pacific Northwest into the northern Rockies late Thursday into
early Friday. This is forecast to result in mountain snows from
western Montana and central Idaho to perhaps as far south as
northern Utah. While not a widespread heavy snow threat, WPC Day
2 probabilities indicate the potential for localized amounts of
8-inches or more across some of the higher elevations.

...Northern Plains...
A remnant shortwave trough associated with the upper low moving
into California on Wednesday is expected to lift northeast out
ahead of the shortwave trough digging into the Northwest on
Thursday. Models have been trending colder over the past few
runs, showing a greater signal for accumulating snows as the
system moves across North Dakota Thursday night, with WPC Day 2
probabilities (ending 12 UTC Fri) now indicating a Slight Risk or
more for accumulations of 4-inches or greater across a large
portion of central and eastern North Dakota. Although the models
have been trending colder, the NAM is relatively cold outlier at
this point -- producing accumulations greater than the model
consensus across North Dakota into central and northern Minnesota.

The probability of significant icing is less than 10 percent.

Day 3...

...Northern and Central Rockies/Northern Plains...
The shortwave trough moving into the northern Rockies on Thursday
will continue to move east into the High Plains on Friday. Low to
mid level frontogenesis and upslope flow may help produce some
high elevation snows from western and central Wyoming and northern
Utah to central Colorado on Friday. Some additional snows are
also possible across northern North Dakota as the upper trough
moves across the state on Friday.

The probability of significant icing is less than 10 percent.

Pereira

$$




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FOUS11 KWBC 032031
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
431 PM EDT Wed Oct 03 2018

Valid 00Z Thu Oct 04 2018 - 00Z Sun Oct 07 2018

Day 1...
...Mountain West...
Upper low off the southern California coast will open and eject
northeast into the northern Plains. Moist advection ahead of this
feature will produce mountain snows across the Rockies, but very
warm temperatures will confine the highest accumulations to
elevations above 8000 ft. WPC probabilities show the potential for
several inches of snow in the highest peaks of the Sierra Nevada,
the Uinta, and the Wind River ranges.

...Northern Plains...
The filling shortwave lifting northeast into the Plains will
induce weak low pressure across Wyoming spawning warm advection
snowfall into the Dakotas Thursday evening. The probability for
snow is highest across south-central North Dakota where the
atmospheric column will initially be entirely below freezing
before slowly warming, but WPC probabilities remain low for
greater than 2 inches of snowfall.

The probability of significant icing is less than 10 percent.

Day 2...

...Northern Plains...
Two distinct shortwave troughs will move across the Northern
Plains on Day 2 producing the potential for accumulating snows.
The first will weaken and lift northeast very early on Friday
creating light accumulations before a more potent trough digs into
the Pacific Northwest and races into the Northern Plains during
the afternoon and evening. The NAM continues to be a cold outlier
with its thermal profiles and produces more snow locally, but the
GFS/ECMWF are in good agreement and keep the warm nose at 850mb
south of most of eastern North Dakota and northern Minnesota.
There is a robust signal for heavy snow in north/eastern North
Dakota where mid-level frontogenesis maximizes in conjunction with
strong omega through a nearly saturated dendritic growth zone, and
high probabilities exist for more than 4 inches of accumulation
with over 6 inches possible. Lower amounts are likely into
Minnesota where the warm air advects farther northward, but high
probabilities remain for 2 inches or more there.

...Northern Rockies...
A shortwave trough lifting NE out of the area early Friday will be
immediately replaced by a more potent trough digging southward
from the Pacific Northwest. This will result in widespread
mountain snows, with the highest potential for heavy snow across
portions of the Rockies in south-central Montana and northwest
Wyoming including Yellowstone and Grand Teton National Parks. WPC
probabilities indicate a high potential for greater than 4 inches
of snow in this region, with up to 12 inches possible in the
highest terrain.

The probability of significant icing is less than 10 percent.

Day 3...

...Pacific Northwest and the Rockies...
Shortwave will dig into the Pacific Northwest and through southern
California amplifying a trough across the western CONUS while
surface high pressure lifts northeast through the Northern Plains.
Return flow around the surface high will increase moisture into
the West as the upper feature and its associated surface
reflection sink southeast along the Pacific Coast. This will
produce high elevation snows across the Rockies, Uintas, and
Bitterroots, as well as in the highest terrain of the Blue
Mountains in Oregon. WPC probabilities also indicate a good chance
for greater than 2 inches of snow in the Cascades of Washington
including Mount Rainier.

The probability of significant icing is less than 10 percent.

Weiss

$$




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FOUS11 KWBC 040723
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EDT Thu Oct 04 2018

Valid 12Z Thu Oct 04 2018 - 12Z Sun Oct 07 2018

Day 1...

...Mountains of south central MT, western WY and northern UT...
Upper level trough forecast to be over NV 12z Thu moves steadily
northeast into the northern Plains. Low-mid level moist advection
ahead of this feature will combine with upper divergence maxima
produce mountain snows across the ranges of northern UT and
western WY early Thu before the wave departs on to the Plains.
WPC probabilities show the potential for several inches of snow in
the highest peaks of the Uinta and the Wind River ranges. A
northern stream trough crossing MT does likewise, with upper
divergence driving a period few snow at higher elevations briefly
in southwest MT and then across south central MT to the WY border.

...Northern Plains...
As the filling shortwave lifts northeast into the Plains, mid
level warm/moist advection develops an leads to snow developing
across the Dakotas into MN. The 18z NAM had heavier snow in MN
thanks to strong 300 mb divergence in the right entrance region of
an upper level jet streak across northern MN to the upper Great
Lakes.
The probability for snow is highest across south-central North
Dakota where the column will initially be entirely below freezing
before slowly warming.

The probability of significant icing is less than 10 percent.

Day 2...

...WY/CO Rockies...
The next system in the series of upper troughs crossing the
intermountain west moves east from the Great Basin across WY and
CO. As an upper jet maxima crosses CO, upper divergence in the
left exit region favors lift across much of southern WY and Co. As
Fri progresses the wave continues east and deamplifies as it moves
on to the Plains, limiting both the duration and intensity of
snow.

...Ranges of Wa/Or...
The next upper trough is forecast to move slowly southeast from
the Pacific Ocean towards the Pacific northwest. Moisture return
ahead of the upper trough combined with upper divergence in the
left exit region jet leads to snow showers in the Wa Olympics and
Cascades, eventually reaching the Blue Mountains.

...Northern Plains...
The area of low-mid level warm/moist advection moves quickly out
of the Dakotas and MN into the Canadian provinces, so the snow
should taper with only minor additional accumulations due to the
steady forward progress of the upper trough.

The probability of significant icing is less than 10 percent.

Day 3...

...Ranges of the Great Basin to the northern and central Rockies...
An amplifying upper trough will depart the Pacific northwest and
cross the northern Rockies and Great basin.
Areas downstream from the trough are expected to be in favored
couplets of 70 mb convergence and 300 mb divergence, leading to
periods of snow in the ranges of ID and then moving into southern
MT, western WY and northern UT.
Several inches of snow are possible where longer duration high
layer relative humidity and lift occur in the ranges of northern
UT across western WY and then moving into western CO Sat night.

The probability of significant icing is less than 10 percent.

Petersen

$$




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FOUS11 KWBC 042039
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 PM EDT Thu Oct 04 2018

Valid 00Z Fri Oct 05 2018 - 00Z Mon Oct 08 2018

Day 1...

...Mountains of south central MT, western WY and northern UT...
Upper level trough forecast to be over NV 12z Thu moves steadily
northeast into the northern Plains. Low-mid level moist advection
ahead of this feature will combine with upper divergence maxima
produce mountain snows across the ranges of northern UT and
western WY early Thu before the wave departs on to the Plains.
WPC probabilities show the potential for several inches of snow in
the highest peaks of the Uinta and the Wind River ranges. A
northern stream trough crossing MT does likewise, with upper
divergence driving a period few snow at higher elevations briefly
in southwest MT and then across south central MT to the WY border.

...Northern Plains...
As the filling shortwave lifts northeast into the Plains, mid
level warm/moist advection develops an leads to snow developing
across the Dakotas into MN. The 18z NAM had heavier snow in MN
thanks to strong 300 mb divergence in the right entrance region of
an upper level jet streak across northern MN to the upper Great
Lakes.
The probability for snow is highest across south-central North
Dakota where the column will initially be entirely below freezing
before slowly warming.

The probability of significant icing is less than 10 percent.

Day 2...

...WY/CO Rockies...
The next system in the series of upper troughs crossing the
intermountain west moves east from the Great Basin across WY and
CO. As an upper jet maxima crosses CO, upper divergence in the
left exit region favors lift across much of southern WY and Co. As
Fri progresses the wave continues east and deamplifies as it moves
on to the Plains, limiting both the duration and intensity of
snow.

...Ranges of Wa/Or...
The next upper trough is forecast to move slowly southeast from
the Pacific Ocean towards the Pacific northwest. Moisture return
ahead of the upper trough combined with upper divergence in the
left exit region jet leads to snow showers in the Wa Olympics and
Cascades, eventually reaching the Blue Mountains.

...Northern Plains...
The area of low-mid level warm/moist advection moves quickly out
of the Dakotas and MN into the Canadian provinces, so the snow
should taper with only minor additional accumulations due to the
steady forward progress of the upper trough.

The probability of significant icing is less than 10 percent.

Day 3...

...Ranges of the Great Basin to the northern and central Rockies...
An amplifying upper trough will depart the Pacific northwest and
cross the northern Rockies and Great basin.
Areas downstream from the trough are expected to be in favored
couplets of 70 mb convergence and 300 mb divergence, leading to
periods of snow in the ranges of ID and then moving into southern
MT, western WY and northern UT.
Several inches of snow are possible where longer duration high
layer relative humidity and lift occur in the ranges of northern
UT across western WY and then moving into western CO Sat night.

The probability of significant icing is less than 10 percent.

Petersen

$$




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FOUS11 KWBC 050736
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Fri Oct 05 2018

Valid 12Z Fri Oct 05 2018 - 12Z Mon Oct 08 2018

Day 1...

...Cascades in Washington to Mountains of southern ID...
The approach of a surface low pressure in advance of the
approaching upper trough will advect Pacific moisture into
Washington state, continuing into southern ID the latter half of
Day 1. This will produce elevation snows in the Cascades with a
few inches of snow possible in the highest terrain, continuing
into the Boise Mountains of ID.

...North Dakota/northern MN.....
Snow occurring across northern ND the last several hours moves
into northeast ND and northwest MN with an initial round of warm
advection near the 700 mb front and then low level convergence in
advance of the approaching 700 mb trough. The steady forward
progression of the trough will limit duration of snowfall with
activity later today departing north of the Canadian border.

The probability of significant icing is less than 10 percent.

Day 2...

...Mountains of ID/UT/southern MT/WY/UT/CO...
The upper trough is forecast to amplify across Nevada and UT with
the slow moving 700 mb front allowing large areas of enhanced
moisture in the frontal circulation with vertical velocity maxima
near the front supporting several inches of snow in the ranges
from southern ID across western WY, UT, and possibly into western
CO. The highest probability for significant snow exists across
the higher terrain of the Uinta and Wind River ranges. The models
indicate a closed 700 mb low forming over UT with lowering
heights/snow levels late Sat night.

The probability of significant icing is less than 10 percent.

Day 3...

...Ranges of UT/CO/WY/adjacent MT...
The upper trough is forecast by most models to contain a slow
moving closed 700 mb low with a few models redeveloping the low
along the trailing front, as well as a few which develop
circulations along the front. At the surface, low pressure will
develop in response to this trough near the four corners region,
driving moist advection on increasing low-level southerly flow.
Mid and upper level forcing due to the low level frontal
circulation and upper divergence will produce strong lift,
enhanced by the moisture fluxes into the higher terrain of
Colorado and Wyoming. Widespread mountain snows are likely with
several inches expected in the highest terrain of the San Juan,
Uinta, and Bighorn mountains.

...Northern Plains...
A deep layer front drifts east across the northern plains in
conjunction with an upper level jet streak.
Lift in the vicinity of the front and jet results in mixed precip
and possibly a period of snow from southeast MT and northeast WY
across portions of western SD/ND. The highest probability for
greater than 4 inches of snow focused across the terrain of the
Black Hills. The model QPF and temperature profile have enough
differences model to model and run to run to result in a spread of
several inches in these areas.

The probability of significant icing is less than 10 percent.

Petersen

$$




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FOUS11 KWBC 052040
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
439 PM EDT Fri Oct 05 2018

Valid 00Z Sat Oct 06 2018 - 00Z Tue Oct 09 2018

Day 1...

...Mountain West...
A surface low pressure will move onshore the Pacific Northwest in
advance of an upper trough and jet maximum. This will bring
increased moisture, as well as lift in the left exit region of
this upper jet, into the Cascades before spilling southwest
through Day 1. The upper trough will amplify and move very slowly
eastward while relative humidity remains high, so mountain snows
are likely. Total snowfall is expected to remain light, with WPC
probabilities for more than 2 inches confined to the highest
elevations of the Wasatch Range in Utah, as well as the Blue
Mountains in Oregon and the Sawtooth Mountains in Idaho.

...Minnesota.....
Shortwave trough will be exiting Minnesota to the northeast early
on Day 1, Friday evening. Snow will persist near the international
border in the vicinity of a 700mb trough racing eastward which
will create light snow accumulations across far northern Minnesota
before dry advection commences by Saturday morning.

The probability of significant icing is less than 10 percent.

Day 2...

...Mountains of ID/UT/CO/WY/Southern MT...
An upper trough will amplify and cutoff across the desert
southwest while moving only slowly to the east. This spawns
surface low pressure development in the lee of the Rockies, with
deep southerly flow driving anomalously high precipitable water
into the mountains, The slow motion of these features combined
with cool temperatures beneath the upper trough will create
persistent and widespread mountain snows. Heavy snow is probable
as jet level dynamics and upslope enhancement combine to create
strong lift across the high terrain of the San Juans, Wasatch,
Unitas, and Bighorns. WPC probabilities across the highest terrain
are high for over 8 inches of snow, and over 12 inches is
possible. However, uncertainty still exists into how low snow
levels will get as the 700mb warm nose of temperatures above 0C
lift northward, especially into Colorado, and this is reflected in
lower probabilities below 8000 feet.

...Black Hills of SD into Western ND...
Upper trough across the west and surface low in the vicinity of
NM/CO will cause increasing potential for heavy snow across the
Black Hills. Anomalously high precipitable water will be focused
on E/SE low-level flow into the terrain, causing significant
upslope enhancement to already robust synoptic and isentropic
lift. The GFS is slower and further NE with its surface low
compared to the NAM/ECMWF, but has support from its ensembles.
This creates a large spread in potential snowfall amounts with the
GFS on the high end. Forecast soundings show deep saturation with
strongest omega through the dendritic growth zone and nearly
isothermal low-levels suggests good dendritic maintenance as well,
so very heavy snowfall rates are possible. For this potential and
the model spread, WPC probabilities are high for moderate snow but
low for heavy accumulations, but the potential exists for greater
than 8 inches of snow in the highest terrain. Lesser amounts are
likely northeast into ND as mid-level vorticity advects to the
northeast.

The probability of significant icing is less than 10 percent.

Day 3...

...Black Hills of SD into ND...
Low pressure near CO/NM will continue to advect anomalously high
moisture and significant snow into the terrain early on Day 3
before mid-level forcing weakens. This causes the low-level front
to shift eastward and the moist advection to shut off, bringing an
end to the snowfall. Strong omega in response to isentropic lift
and mid-level diffluence will continue the potential for heavy
snows, especially in the favored upslope regions of the Black
Hills. WPC probabilities are highest for greater than 4 inches of
snow in the high terrain, with lower probabilities northeast along
the low-level FGEN boundary to the northeast.

...Ranges of UT/CO/WY/adjacent MT...
Upper trough will remain across the Mountain West into Monday
evening. Mid level forcing due to spokes of vorticity rotating
around the mean trough, as well as jet level divergence will
support widespread mountain snows in an environment characterized
by strong low-level moist advection. The highest snow amounts are
likely in the high terrain of the Uintas, San Juans, Colorado
Rockies, and Laramie Mountains of Wyoming, where WPC probabilities
are greatest for 8 inches of snow. With the upper trough sinking
well into Arizona, some lighter snows are possible even into the
high terrain of the Kaibab Plateau and Mogollon Rim.

The probability of significant icing is less than 10 percent.

Weiss

$$




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FOUS11 KWBC 060828
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Sat Oct 06 2018

Valid 12Z Sat Oct 06 2018 - 12Z Tue Oct 09 2018

Day 1...

...Ranges of ID/MT/WY/UT/CO...
An upper level trough gradually strengthens as it moves across the
Great Basin. The NAM shows a closed 700 mb low developing along
the front in UT. Low level convergence in the vicinity of the
front and possible low leads to
a QPF and snow maxima in the northern Wasatch and Uintas of UT,
with a secondary maxima in the ranges of southwest MT near the
front. Lighter totals are expected further east due to limited
duration of snow in the ranges of eastern WY, western CO, and
southern ID.

The probability of significant icing is less than 10 percent.

Day 2...

...Mountains of UT/CO/WY/Southern MT...
An upper trough will amplify and cutoff across the desert
southwest while moving only slowly to the east.
The closed 700 mb low drifts east across UT towards the CO border
with the 700 mb front north of the low drifting east across WY.
Lift provided by the front and upper jet combines with orographic
influences to generate mountain snows. Heavy snow is probable as
jet level dynamics and upslope enhancement combine to create
strong lift across the high terrain of the San Juans, Wasatch,
Unitas, and Bighorns. WPC probabilities across the highest terrain
are high for over 8 inches of snow, and over 12 inches is
possible. However, uncertainty still exists into how low snow
levels will get east of the low/front, and this is reflected in
lower probabilities below 8000 feet.

...Western SD across Western ND...
The approaching low level front and moisture convergence will
cause increasing potential for heavy snow across the Black Hills.
Anomalously high precipitable water will be focused on E/SE
low-level flow into the terrain, causing significant upslope
enhancement to synoptic lift. There remains a large spread in
potential snowfall amounts with the NAM and ECMWF showing lower
amounts and GFS/GEFS Mean on the high end across northeast WY into
the western Dakotas.

WPC probabilities are highest for heavy snow at higher elevations
but low for heavy accumulations at lower elevations. Lower amounts
are likely northeast into ND as initial temperatures are too warm
for snow with dual QPF and temperature profile uncertainties.

The probability of significant icing is less than 10 percent.

Day 3...

...Ranges of UT/CO/WY/adjacent southern MT...
The upper trough will drift east across Colorado and NM. Mid level
forcing due to spokes of vorticity rotating around the mean trough
support light to moderate mountain snows. The highest snow
amounts are likely in the high terrain of the Uintas, San Juans,
Colorado Rockies, and Laramie Mountains of Wyoming, where WPC
probabilities are greatest for 8 inches of snow.

...Mountains of northwest MT...
The models show confluent flow over British Columbia and the
Pacific northwest, with a 300 mb jet streak that comes south into
Wa and then OR that in turn induces upper divergence in the left
exit region of the jet. The lift from the upper divergence causes precipitation to develop over the Pacific Northwest and then
northern Rockies, with snow likely in higher elevations of
northernmost ID and northwest MT, including Glacier National
Park/Rocky Mountain front. Greater weighting was given to the
stronger closed low forecasts of the ECMWF, supported by UKMET,
although odds are the UKMET is too deep with its 500 mb low.

...Black Hills of SD into ND...Southeast MT
Lighter snows are expected on day 3 in the western Dakotas to
southeast MT as the northern stream trough drifts east with tepid
700 mb vertical motions in the region and stronger ascent in areas
that are too warm for snow in the central Plains.

The probability of significant icing is less than 10 percent.

Petersen


$$




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FOUS11 KWBC 062041
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
440 PM EDT Sat Oct 06 2018

Valid 00Z Sun Oct 07 2018 - 00Z Wed Oct 10 2018

Day 1...

...Ranges of ID/MT/WY/UT/CO...
An upper level trough will amplify over the Great Basin in
response to a shortwave digging into its base. This will initiate
low-level cyclogenesis with warm advection occurring east of the
low into CO and WY. Synoptic forcing due to vorticity advection
and upper diffluence will combine with increasing isentropic lift
to produce widespread mountain snows. Warm temperatures of above
0C at 700mb flooding into much of CO and southeast WY will limit
snow to the highest terrain. WPC probabilities for greater than 4
inches of snow are highest NW of the 700mb low into the Uintas of
UT and Bighorns in WY, with lighter amounts likely across much of
the other mountain ranges.

...Western SD into southwest ND...
Sharpening 500mb trough will induce a closed 850-700mb low to
funnel warm moist air into the High Plains the latter half of Day
1. A shortwave will eject from the mean trough to lift northeast
and overhead the western Dakotas coincident with strengthening
mid-level frontogenesis and 700mb deformation to provide a brief
period of robust omega. The forcing will be of relative short
duration as the shortwave lifts quickly northeast, so WPC
probabilities are low for more than 2 inches of snow, with the
best chance in the high terrain of the Black Hills.

The probability of significant icing is less than 10 percent.

Day 2...
...Mountains UT/CO/WY/AZ...
Anomalously strong upper trough will cutoff over the desert SW and
migrate slowly eastward Sunday. 700mb reflection of this low will
move concurrently with the upper trough, driving warm moist
advection into the Mountains. The 700mb temperatures climb well
above 0C east of this low, so some uncertainty remains in the
eastern extent of snowfall in Colorado, but to the north and west
the potential exists for significant accumulation of greater than
6 inches in the high terrain of the San Juans, Uintas, and
Laramies. Lesser amounts are likely below 6000 feet.

...Western SD into Central ND...
Warm moist advection ahead of a closed mid-level low will combine
with upper diffluence to produce lift and snow into the High
Plains. A spoke of vorticity ejecting northeast from the amplified
upper trough will combine with 700mb deformation to spawn a region
of snow lifting across the Dakotas with light snow accumulations
possible. In the terrain of the Black Hills, subtle upslope
enhancement will increase snowfall potential, and WPC
probabilities are highest in this terrain for up to 4 inches of
snow.

The probability of significant icing is less than 10 percent.

Day 3...

...Ranges of UT/CO/WY/northern NM...
Upper trough will gradually fill and begin to eject eastward in
response to a potent shortwave and jet maximum digging into the
Pacific Northwest. Weak vorticity advection and increasing upper
diffluence in the left exit region of the approaching jet will
support light to moderate mountain snows. The highest WPC
probabilities are across the high Rockies in Colorado as well as
the Uintas in Utah, but much of the high terrain has the potential
to see accumulating light snow.

...Pacific Northwest mountains into western MT...
300mb jet maximum will push southeast from Canada, inducing lift
within the left exit region as it drops into the Pacific
Northwest. Precipitation will develop in response to this synoptic
forcing, initially across the Cascades of Washington before
shifting into the northern Rockies. The greater snowfall is
expected across the Rockies in the vicinity of Glacier National
Park, where 6" of snow is possible above 7000 ft.

...Western High Plains...
Upper trough will gradually deamplify and lift northeast spawning
cyclogenesis across Texas. Deep layer warm advection ahead of this
low will increase moisture into the plains and as the low
strengthens there is potential for increasing snow within the
deformation zone of the developing baroclinic leaf across portions
of Nebraska and South Dakota. Strong lift is possible, but models
still diverge considerably into timing and location of best QPF so
WPC probabilities remain low for more than 2 inches of
accumulation.

The probability of significant icing is less than 10 percent.

Weiss


$$




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FOUS11 KWBC 070827
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Sun Oct 07 2018

Valid 12Z Sun Oct 07 2018 - 12Z Wed Oct 10 2018

Day 1...

...Ranges of southern MT/WY/UT/CO...
An upper level trough will amplify over the Great Basin. This will
initiate low-level cyclogenesis with warm advection occurring east
of the low into CO and WY. Synoptic forcing due to vorticity
advection and upper difluence will combine with the frontal
circulation to produce mountain snows. Warm temperatures of above
0C at 700mb across much of CO and southeast WY will limit snow to
the highest terrain. WPC probabilities for greater than 4 inches
of snow are highest in the Uintas of UT and San Juans of CO, with
lighter amounts likely across the other mountain ranges.

...Western SD into southwest ND...
A sharpening 500mb trough will induce warm/ moist air advection
into the High Plains. A shortwave will eject from the mean trough
to lift northeast through the western Dakotas coincident with
strengthening mid-level frontogenesis and 700mb deformation to
provide ascent. Initial temperature are too warm for snow so the
duration of snow is uncertain.
Amounts are likely to be low most areas with the best chance of
higher totals in the high terrain of the Black Hills.

The probability of significant icing is less than 10 percent.

Day 2...

...Mountains of UT/CO/WY...
Anomalously strong upper trough will migrate slowly eastward
across the southwest and four corners region into the CO/NM
Rockies, with the 70 mb front drifting east across ND and WY, with
post-frontal cooling in WY allowing a transition to snow. The
potential exists for significant accumulation of greater than 6
inches in the high terrain of the San Juans, Uintas, Laramies, and
Snowy Range. Lesser amounts are likely below 6000 feet.

...Western SD into Central ND...
Warm moist advection ahead of a closed mid-level low will combine
with upper diffluence and the low level frontal circulation to
produce lift and snow into the High Plains. Light snow
accumulations are possible, with near surface temperature
uncertainties leading to differences in accumulations, with the
NAM Conus Nest and 00z GFS a few inches higher than the parent NAM
and ECMWF. In the terrain of the Black Hills, upslope enhancement
will increase snowfall potential, and WPC probabilities are
highest here.

...Pacific Northwest mountains into western MT...
A 300mb jet maximum will push southeast from Canada, inducing lift
within the left exit region as it drops into the Pacific
Northwest. Precipitation will develop in response to this synoptic
forcing, initially across the Cascades of Washington before
shifting into the northern Rockies. Accumulating snowfall is
expected across the Rockies in the vicinity of Glacier National
Park, with total amount limited by the short duration of snow this
period.

The probability of significant icing is less than 10 percent.

Day 3...

...Ranges of MT/ID/UT/CO/WY/northern NM...
The initial upper trough will gradually fill and begin to eject
eastward in response to a potent shortwave and jet maximum digging
across the Great Basin. The new upper trough amplifying as it
crosses from ID and NV across western MT, southeast ID, and
northern UT results in cyclonic vorticity advection and increasing
upper difluence/embedded upper divergence in the left exit region
of the approaching jet to support mountain snows. The highest WPC
probabilities are across the high Rockies in Colorado, and in the
northern Wasatch of Ut/Uintas/ranges of western WY and western MT,
including the Rocky Mountain front, where several inches of snow
is possible Tue-Tue night.

...Northern Plains...
The Upper trough will gradually deamplify and lift northeast. Lift
is expected within the frontal circulation for snow within the
deformation zone across Eastern WY across South Dakota and into
North Dakota. The models still diverge considerably into timing
and location of QPF and duration of how long it is cold enough for
snow so WPC probabilities remain low for 4 or more inches of snow.


The probability of significant icing is less than 10 percent.

Petersen


$$




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FOUS11 KWBC 072017
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 PM EDT Sun Oct 07 2018

Valid 00Z Mon Oct 08 2018 - 00Z Thu Oct 11 2018

Day 1...

...Ranges of southern MT/WY/UT/CO...
Deep upper trough across the Great Basin will migrate slowly
eastward while spokes of vorticity rotate through the base and
eject to the northeast. S/SE flow around surface trough
development in the lee of the Rockies will drive warm and moist
air into the mountains. 700mb temperatures across eastern CO and
into eastern WY will climb above 0C, but the mountains just NW of
this axis have the potential to see significant snowfall as
synoptic lift is aided by forced upslope enhancement. Snow levels
across CO will likely remain above 9000 feet before lowering late,
confining the highest snow amounts to the San Juans. Snow levels
may be considerably lower, down to 4000 feet in WY/UT so more
widespread snow is likely there with WPC probabilities indicating
a good chance for greater than 4 inches of snow in the Laramies of
WY, as well as the Uintas in Utah, with more than 8 inches
possible in WY.

...Western SD into central ND...
A shortwave will eject from the Great Basin upper trough and lift
across the northern Plains. This vorticity lobe will be
accompanied by diffluence within the right rear quadrant of a
300mb jet max moving atop a moist airmass as high PWAT gets
advected into the region ahead of a low pressure in the lee of the
Rockies. A swath of snow is probable across western SD through
central ND along the 700mb deformation axis which will maximize
lift despite moderate QPF. Some enhancement is possible across the
Black Hills where easterly upslope flow occurs, but WPC
probabilities will generally remain low for more than 2 inches of
snowfall outside of the Black Hills.

...Freezing Rain...
A small area ice accretion is becoming more likely from western WY
into the Panhandle of NE and western SD. As 700mb warm advection
commences, cold air banked into the terrain will be slow to erode
due to reinforcement of cooler and drier air within a wedge of
high pressure funneling down from the north. Saturation on
forecast soundings is shallow, but with 700mb temps to +4C and
sub-freezing surface temperatures, a 6-12 hour window exists for
freezing drizzle which could accrete up to a few hundredths of an
inch. WPC probabilities for one-tenth of an inch of ice accretion
remain very low.

Day 2...

...Mountains of UT/CO/WY/NM...
Upper trough across the west will migrate eastward pushing a
Rockies lee low pressure into the Plains. Lift from vorticity
effects as well as jet level diffluence will produce mountain
snows, especially the first half of day 2 before drier air advects
into the region from the west. Accumulations of greater than 4
inches are possible in the high terrain of the San Juans, Colorado
Rockies, and Uintas. Lesser amounts are likely below 7000 feet.

...Northern Plains...
Low pressure in the lee of the Rockies will fill and transition to
the east while 700mb warm advection persists into the Dakotas.
Synoptic lift beneath a departing 300mb right entrance region and
the aforementioned warm advection will be aided by isentropic
ascent to produce snowfall. Temperatures initially are marginal
but will cool through the morning so light snow is likely across
much of western SD into southwest ND, with the highest
probabilities for over 2 inches of snow focused in the terrain of
the Black Hills.

...Pacific Northwest mountains into western MT...
Potent 300mb jet maximum will dive southeast from Canada, inducing
lift within the left exit region as it drops into the Pacific
Northwest. Precipitation will develop in response to this synoptic
forcing, with widespread high elevation snow likely across the
high Cascades of WA as well as the northern Rockies of MT and ID.
Total QPF is expected to be light, but many locations above 7000
feet have the potential to see more than 2 inches of snow. A
better probability for over 4 inches exists on the eastern side of
the northern Rockies in Montana near Glacier National Park, where
a prolonged period of easterly upslope flow is expected to enhance
snowfall accumulations.

The probability of significant icing is less than 10 percent.

Day 3...

...Northern and Central Rockies...
Potent shortwave and associated jet max will dig southeast into
the longwave trough across the west. As this feature races
eastward, it will force synoptic ascent into a moist environment,
aided by weak 700mb deformation across WY. Widespread mountain
snows are likely from the MT Rockies southward into Utah and
Colorado. The highest amounts are likely in the high terrain of
northwest Wyoming, including the Tetons and Wind Rivers, where
isentropic upglide is maximized. Here, WPC probabilities are high
for 8 inches of snow or more. Lesser amounts are likely elsewhere
above 6000 feet.

...Northern Plains...
Low pressure will develop near Iowa in response to a negatively
tilting upper trough rotating through the Central Plains. As this
surface low deepens and lifts into the Great Lakes, mid-level
frontogenesis will increase in conjunction with the deformation
axis NW of the low center. Robust ascent will accompany this
feature despite weak jet level dynamics, and a stripe of heavy
snow within the developing comma head is possible from far eastern
ND into northern MN. Uncertainty still exists into the placement
and intensity of this axis, and this is reflected by only moderate
WPC probabilities for more than 4 inches of snow.

The probability of significant icing is less than 10 percent.

Weiss


$$




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FOUS11 KWBC 080815
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Mon Oct 08 2018

Valid 12Z Mon Oct 08 2018 - 12Z Thu Oct 11 2018

Day 1...

...Ranges of WY/UT/CO...
The models show a closed 700 mb low near the CO/UT border drifting
slowly northeast and weakening Monday night, possibly into an open
wave. The initial precipitation with higher elevation snow starts
with 700 mb convergence and 300 mb divergence in CO and northern
UT that then drifts into WY along the low level frontal boundary,
with net 24 hour liquid equivalent amounts a bit higher in WY with
longer duration precip. WPC probabilities indicating a good chance
for greater than 4 inches of snow in Laramie and Snowy ranges of
WY. Snow continues to be elevation dependent with lower amounts
in valleys.

...Western SD into central ND...
A shortwave will eject from the Great Basin upper trough and lift
across the northern Plains near the low level front. This
vorticity lobe will be accompanied by difluence within the right
rear quadrant of a 300mb jet max moving atop a moist airmass. A
swath of snow is probable across western SD through central ND
along the 700mb deformation axis which will maximize lift, with
near-sfc temps borderline for snow. Some enhancement is possible
across the Black Hills where easterly upslope flow occurs, with
higher snow totals partly due to higher elevations increasing
chances precipitation would be snow longer. The 00z NAM suggests
precip in western SD becomes snow with a burst of ascent Mon
night. Most guidance indicates potential for 2-4 inches.

...Light Freezing Rain/drizzle in parts of Western SD/Western
NE/Southeast WY...
Patches of light ice accretion are possible from the Panhandle of
NE across western SD to southeast WY. As 700mb warm advection
commences, cold air banked into the terrain will be slow to erode
due to reinforcement of cooler and drier air within a wedge of
high pressure funneling down from the north. Saturation on
forecast soundings is shallow, but with 700mb temps to +4C and
sub-freezing surface temperatures, a 6-12 hour window exists for
freezing drizzle which could accrete up to a few hundredths of an
inch. WPC probabilities for one-tenth of an inch of ice accretion
remain very low.

The probability of a quarter inch of icing is less than 10 percent.

Day 2...

...Mountains of MT/ID/northern UT/CO/WY...

Potent 300 mb jet maximum will induce lift within the left exit
region as it drops across the northern Great Basin, with 300 mb
divergence maxima crossing southern ID and into northern UT.
Precipitation will develop in response to this synoptic forcing,
with widespread high elevation snow likely across the ranges of
southern ID, spreading into the ranges of western WY and then
northern UT. The highest amounts are likely in the high terrain
of southern ID, western Wyoming, and northern UT including the
Tetons, and northern Wasatch in UT. Here, probabilities show
potential for 8 inches of snow or more.

Further north, snow is expected to develop in the front range of
the MT Rockies partly due to the 700 mb front moving across the
region and partly due to return flow with an easterly component
casing upslope conditions on the Rocky Mountain front. A better
probability for over 4 inches exists on the eastern side of the
northern Rockies in Montana in the Lewis Range/Glacier National
Park.

...Northern Plains...
Low pressure will develop in the MS Valley in response to a
negatively tilting upper trough rotating through the Central
Plains. As this surface low deepens and lifts into the upper MS
Valley, mid-level frontogenesis north of the low will increase in
conjunction with the deformation axis NW of the low center. Robust
ascent will result, and a stripe of snow develops in eastern ND
into northern MN. Uncertainty still exists into the placement and
intensity of this axis, plus initial temps may be too warm for
snow before cooling aloft increases confidence snow will occur,
and this is reflected by low WPC probabilities for more than 4
inches of snow. Further south, temperatures are expected to be
too warm for snow in much of southeastern SD and southern MN.

The probability of significant (quarter inch or more) icing is
less than 10 percent.

Day 3...

...Ranges of northern UT and CO across WY to southern MT...
As the upper trough moves east out of ID and UT, the upper jet is
forecast to cross northern CO, placing WY within the area favored
for greatest upper divergence. Snows are expected in advance of
the upper trough early on Wed in WY and wind down once the upper
trough departs onto the plains Wed night. Several additional
inches are possible in the ranges of WY from the Wind River across
the Snowy/Laramie mountains. Light snow persist near the cyclonic
shear axis with modest low level convergence in the Tetons to
ranges of southeast ID/southwest MT.

...Northern MN/adjacent eastern ND...
The models show low pressure moving out of the upper MS Valley to
the upper Great Lakes and across the border into Canada. The
ongoing snow in northeastern ND and northern MN continues early
this period and winds down as the mid level level front and convergence/deformation move north out of the region and ascent
weakens. There is potential for several inches of snow in
northwest MN, supported by multiple models.

The probability of significant icing is less than 10 percent.

Petersen



$$




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FOUS11 KWBC 220755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Mon Oct 22 2018

Valid 12Z Mon Oct 22 2018 - 12Z Thu Oct 25 2018


Days 1 through 3...

***Central Rockies***

The broad upper level trough currently over central California is
forecast to slowly move east with some positive vorticity
advection within the base of the trough. As the upper level
trough approaches the Four Corners region by Tuesday, moisture
advection and mid level dynamics are maximized over western
Colorado and will result in the greatest opportunity for
accumulating snow for elevations above 10000 feet. The San Juan
Mountains will likely have the greatest amounts, with patchy areas
of greater than 4 inches possible above treeline by Wednesday
morning for southwest facing slopes. Light snow amounts are also
expected for the Uinta Mountains in northeast Utah.


***Northern New England***

A strong shortwave impulse tracking southeastward across Ontario
Monday is forecast to amplify further upon reaching New England by
Tuesday night. The accompanying surface low is expected to
re-form near Nova Scotia by early Wednesday morning and intensify
as it lifts towards the north. A band of moderate snow is likely
to the north and west of the surface low across northern Maine and
extending westward to the White Mountains of northern New
Hampshire, with the greatest snowfall associated with where the
low-mid level frontogenesis sets up. There is a moderate
probability of 4+ inches across northern Maine Tuesday night and
into Wednesday morning.

The probability of significant icing (0.25 inches or more) is less
than 10 percent all three days.

Hamrick


$$




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FOUS11 KWBC 222020
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Mon Oct 22 2018

Valid 00Z Tue Oct 23 2018 - 00Z Fri Oct 26 2018


Day 1...

...Central Rockies...
Broad upper level trough across the west will shift eastward
through Day 1. Increasing moist advection on return flow ahead of
this feature will combine with the best jet level dynamics due to
right entrance region diffluence, to produce snowfall in the
highest terrain of Colorado and Utah. Accumulations will be
limited to the terrain above 9000 feet, and will be maximized
across the San Juans where orographic enhancement is likely on
southerly and moist 700mb winds. WPC probabilities are high for 4
inches of snow across the San Juans with 8 inches or more
possible. Lower amounts are likely in the high terrain of the
Rockies and Sangre De Cristos in Colorado, as well as the Uintas
in northeast Utah.

The probability of significant icing (0.25 inches or more) is less
than 10 percent.

Day 2...

...Northern New England...
Potent shortwave digging into New England will induce surface
cyclogenesis which will then lift northeast while strengthening
into New Brunswick, Canada. Heavy snow will develop within the
primary mid-level deformation axis northwest of the 700mb low
across far northern New Hampshire and much of northern Maine.
Although there remains some disagreement into the exact placement
of this heaviest band of snow, the best overlap of lift due to
height falls, sloped mid-level frontogenesis, and the presence of
a modest trowal occurs over far northern Maine. Here, WPC
probabilities show a moderate risk for more than 8 inches of snow.
Elsewhere across northern New England including the White
Mountains of NH, WPC probabilities are moderate for 4 inches of
snow.

...Central Rockies...
Upper trough will continue to slide eastward across the Four
Corners region Tuesday night before shifting into the Plains on
Wednesday. Moist advection will persist ahead of this feature
before the trough axis slides east, bringing with it drier air and
an end to the mountain snows. Jet level diffluence and subtle PVA
within a moistening column will produce high elevation snows
across the Colorado Ranges as well as the Sangre De Cristos in New
Mexico. The highest amounts are likely in the San Juans where WPC
probabilities are high for 4 or more inches of snow. Lighter
snowfall accumulations are likely elsewhere across most of the
high terrain above 9000 feet.

The probability of significant icing (0.25 inches or more) is less
than 10 percent.

Day 3...

...Northern New England...
Vertically stacked low pressure will drift slowly northeast away
from Maine on Day 3. Residual deformation snows are likely
Wednesday night across far northern Maine but WPC probabilities
are low for more than just a few inches of additional accumulation
before forcing lifts away and drier air advects in from the west.

The probability of significant icing (0.25 inches or more) is less
than 10 percent

Weiss


$$




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FOUS11 KWBC 230742
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
342 AM EDT Tue Oct 23 2018

Valid 12Z Tue Oct 23 2018 - 12Z Fri Oct 26 2018


Days 1-3...

Central Rockies
---------------
A broad upper level trough in the vicinity of the Four-Corners
region on Tuesday will have a modest advection of moist 700mb
southerly inflow combined with favorable upper level dynamics.
Although most locations are expected to get rain with this system,
the highest elevations of the San Juan, Sawatch, and Sangre de
Cristo mountains in Colorado will likely have some snow above
9000-10000 feet, with amounts approaching 4 inches for the higher
peaks. Drier conditions return to the region for the Day 2 period
on Wednesday.


Northern New England
--------------------
The first noteworthy winter weather event of the season is
expected for much of northern New England for Tuesday night and
extending into Wednesday. A potent shortwave disturbance tracking
across Ontario will induce surface cyclogenesis over the Gulf of
Maine Tuesday evening. This surface low will intensify as it
lifts northeastward towards New Brunswick, Canada, and the upper
level trough acquires negative tilt. A well defined deformation
zone northwest of the low along with low-mid level frontogenesis
is expected to produce a swath of moderate snow extending from
northern Vermont and New Hampshire to northwestern Maine.

There is some indication in the model guidance, particularly the
00Z NAM, that a brief period of mixed precipitation will be
possible across these same areas before the transition to all
snow. NAM model soundings suggest a modest 925-850mb inversion
above a sub-freezing boundary layer, which may result in some
light freezing rain in interior valley locations on the order of a
few hundredths of an inch.

Many GEFS and EC ensemble members are indicating the potential for
at least 4 inches of snow from northern New Hampshire to northern
Maine, with some also indicating the potential for 8 inch amounts,
with the greatest accumulations likely north of the Canadian
border. The WPC probabilities indicate a moderate to high
potential for greater than 4 inches from the White Mountains of
New Hampshire to Aroostook County, Maine.

The probability of significant icing (0.25 inches or more) is less
than 10 percent for all three days.

D. Hamrick


$$




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