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Mesoscale Discussion 1450
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   Mesoscale Discussion 1450
   NWS Storm Prediction Center Norman OK
   1042 AM CDT Mon Aug 10 2020

   Areas affected...Portions of northern/eastern IA...southern
   WI...northern/central IL...and far northeastern MO

   Concerning...Severe potential...Severe Thunderstorm Watch likely 

   Valid 101542Z - 101715Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Widespread damaging winds, some potentially significant
   (75+ mph), will become increasingly likely as a line of storms moves
   quickly eastward this afternoon. A Severe Thunderstorm Watch will be
   needed to address this threat, and an upgrade to Moderate Risk (for
   significant severe/damaging winds) will be issued with the upcoming
   1630Z update to the Day 1 Convective Outlook.

   DISCUSSION...A compact MCS moving into central IA as of 1540Z has
   recently produced numerous severe/damaging wind gusts. Recent radar
   trends suggest this system has already become very well organized,
   with the development of an 80-100+ kt rear-inflow jet only a couple
   thousand feet off the surface per KDMX velocity data. The airmass
   downstream of this MCS into eastern IA, southern WI, and
   northern/central IL is already quite unstable, with MLCAPE of
   2000-2500 J/kg present per 15Z mesoanalysis estimates. Additional
   diurnal heating of this airmass is expected to yield very strong to
   potentially extreme instability by this afternoon, with MLCAPE
   potentially reaching the 3500-5500 J/kg range by peak heating.
   Recent VWPs from the KDMX radar show sufficient mid-level flow
   (around 30-35 kt) to support the continued intensity of the ongoing
   MCS.

   Additional storms have recently formed across parts of north-central
   into northeastern IA along a weak cold front. Current expectations
   are for the MCS in central IA to eventually merge with the new
   development in north-central/northeastern IA. Result of this will
   likely be a large, very well organized bow echo producing widespread
   severe and damaging wind gusts across parts of eastern IA into
   southern WI, and northern/central IL. The forecast combination of
   very strong to extreme instability with adequate deep-layer shear
   downstream of the ongoing MCS strongly suggests that a swath of
   potentially significant severe wind gusts of 75+ mph is becoming
   increasingly likely this afternoon across parts of these areas. A
   new Severe Thunderstorm Watch will be needed downstream of the
   current watch in central IA within the next hour or two. An upgrade
   to Moderate Risk for numerous significant severe/damaging wind gusts
   will be issued with the 1630Z update of the Day 1 Convective
   Outlook.

   ..Gleason/Grams.. 08/10/2020

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

   ATTN...WFO...LOT...ILX...MKX...DVN...ARX...

   LAT...LON   40409210 42959200 42989298 43469189 43479023 43388772
               42658767 41638757 40528754 40128821 40179051 40409210 

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Page last modified: August 10, 2020
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