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ACUS11 KWNS 212029
SWOMCD
SPC MCD 212028
WYZ000-MTZ000-IDZ000-212200-

Mesoscale Discussion 0812
NWS Storm Prediction Center Norman OK
0328 PM CDT Thu Jun 21 2018

Areas affected...Eastern Idaho...Southern and Central Montana...and
Northwest Wyoming

Concerning...Severe potential...Watch unlikely

Valid 212028Z - 212200Z

Probability of Watch Issuance...20 percent

SUMMARY...Numerous storms have developed this afternoon and
additional storms are expected to develop through the rest of the
afternoon and into the evening. The primary threat from these storms
will be isolated large hail and damaging winds.

DISCUSSION...Thus far, storms have primarily developed on the higher
elevations of the Bitterroot Mountains in Idaho, and Lewis and Clark
National Forest and Old Baldy in central Montana. However, RAP
forecast soundings indicate the cap breaking in the lower elevations
of southwest Montana and eastern Idaho between 20Z and 21Z. This
increasingly uninhibited boundary layer can be seen on the latest
GOES 16 visible satellite imagery as the low-level cumulus field
expands in northeast Idaho and southwest Montana. Therefore, expect
storms over the higher elevations to remain better sustained as they
move away from the higher terrain. Additionally, expect storms to
develop in the lower elevations in the next few hours ahead of the
vorticity max which is currently in eastern Idaho.

MUCAPE of 1000 to 2000 J/kg and deep layer shear of 35 to 40 knots
support an organized severe risk. However, deconstructive
interactions between the large number of storms, and increasing
cloud cover from early convective initiation limiting additional destabilization will mitigate a more widespread severe threat. The
inverted-v sounding and steep mid-level lapse rates (~7 C/km to 8
C/km per 12Z Boise RAOB and latest RAP analysis) support both a hail
and damaging wind threat from any stronger storms. The best
opportunity for strong to severe storms will remain in areas where
cloud cover is limited and continued heating leads to pockets of
greater instability. The latest visible satellite and HRRR guidance
indicate areas near Billings may have the best opportunity for
strong to severe storms as cloud cover remains limited and low-level southeasterly flow has increased boundary layer moisture.

..Bentley/Dial.. 06/21/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BYZ...GGW...RIW...TFX...PIH...MSO...

LAT...LON 43841337 44541270 45371235 46131222 46791200 47651151
47871101 48111047 48140939 47880866 47580835 46940773
46250739 45410718 44640730 44070772 43700824 43330888
43231051 43451218 43551321 43841337



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