SPC MD 1806



MD 1806 CONCERNING SEVERE THUNDERSTORM WATCH 601… FOR IOWA

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Mesoscale Discussion 1806
NWS Storm Prediction Center Norman OK
0308 AM CDT Tue Aug 20 2019

Areas affected...Iowa

Concerning...Severe Thunderstorm Watch 601...

Valid 200808Z - 200945Z

The severe weather threat for Severe Thunderstorm Watch 601
continues.

SUMMARY...Thunderstorms are developing across northwest Iowa. With
time these thunderstorms should congeal into a complex that will
move southeast through the morning. Large hail, damaging winds, and
a brief tornado will be possible with the early morning storms,
before a transition to primarily a damaging wind threat becomes
likely later this morning.

DISCUSSION...Persistent warm-air advection atop a
northwest-to-southeast oriented warm front across western Iowa has
resulted in elevated thunderstorms developing across northwest Iowa.
The thunderstorms are tapping into a CAPE reservoir in excess of
5000 J/kg and are located in the presence of 40-55 knots of
deep-layer shear. Given this thermodynamic and kinematic
environment, along with midlevel lapse rates around 8-8.5 C/km,
supercells capable of large hail and gusty thunderstorm winds, and a
brief tornado will be possible. 

With time, increasing coverage of thunderstorms and congealing
thunderstorm outflows should promote the upscale growth toward a
mesoscale convective system (MCS). The resulting MCS should
develop/move east-southeast with time -- generally along and north
of the warm front -- with an increasing threat for strong
thunderstorm winds despite being near the climatological minimum in
surface wind potential given the time of day.

..Marsh.. 08/20/2019

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

ATTN...WFO...DVN...ARX...DMX...EAX...FSD...OAX...

LAT...LON   42479646 42739662 43159641 43289657 43499657 43499349
            43299351 43259301 42959301 42909254 42329252 42279233
            41549229 41499242 41189240 41179219 40579218 40569490
            41179492 41199521 41499516 41519545 41609556 41869555
            41899616 42479646 

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