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ACUS11 KWNS 201647
SWOMCD
SPC MCD 201646
ILZ000-KYZ000-TNZ000-MSZ000-MOZ000-ARZ000-201845-

Mesoscale Discussion 1325
NWS Storm Prediction Center Norman OK
1146 AM CDT Mon Aug 20 2018

Areas affected...Southeast MO...northeast AR...western TN...western KY...southern IL...and northwest MS

Concerning...Severe potential...Watch likely

Valid 201646Z - 201845Z

Probability of Watch Issuance...80 percent

SUMMARY...WW issuance is likely by early afternoon across southeast
Missouri, northeast Arkansas, western Tennessee, western Kentucky,
southern Illinois, and perhaps northwest Mississippi, as a
severe-weather threat is expected to develop from thunderstorms that
form across this region and spread east. All severe hazards are
possible, though damaging winds should be the primary threat.

DISCUSSION...Visible satellite imagery showed limited cloudiness
across central AR in the wake of thunderstorms and sufficient breaks
in clouds and/or dissipating clouds across northern AR into
southeast MO to sustain strong diabatic heating into the afternoon.
Despite weak midlevel lapse rates, high moisture content air
(precipitable water near or greater than 2 inches and surface
dewpoints into the lower 70s F) extending north into the middle
MS/lower OH Valleys and surface heating will result in moderate
destabilization which is already present northward across AR.
Further warming of surface temperatures will boost buoyancy across
the northern portions of the discussion area through the afternoon
to support thunderstorm development.

Meanwhile, the convection advancing across southern MO this morning,
as detected by satellite and mosaic radar imagery, is likely
indicating the leading extent of forcing for ascent spreading into
the Ozarks/Mid-South region today. This is attendant to a shortwave trough/speed max rounding the base of the central U.S. cyclone, with
WSR-88D VWP data from southern MO to eastern OK showing
strengthening westerly winds (40-50 kt) around 700 mb. This ascent
and a cold front advancing east across the discussion area this
afternoon and evening will result in a broken line of strong to
severe storms advancing eastward. An increase in effective bulk
shear (up to 35-40 kt) with shear vectors oriented across the front
suggest embedded supercells will be possible in the line of storms. Strengthening southwesterly 850-mb winds will favor low-level
rotation and a tornado threat, while strong, damaging winds may be a
greater threat, given the potential for bowing structures.

..Peters/Hart.. 08/20/2018

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

ATTN...WFO...PAH...ILX...MEG...JAN...LSX...LZK...SGF...

LAT...LON 35159195 36889153 37949096 38919057 38989000 38968923
38848861 38588814 37988821 36768856 34938925 34078998
34049058 34229203 35159195



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