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Mesoscale Discussion 1440
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   Mesoscale Discussion 1440
   NWS Storm Prediction Center Norman OK
   0518 PM CDT Thu Aug 03 2017

   Areas affected...Southern WI...extreme eastern IA...and
   northern/central IL

   Concerning...Severe potential...Watch unlikely 

   Valid 032218Z - 040045Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Isolated strong to severe storms will be possible into the
   early evening, with hail and locally strong wind gusts being the
   primary threats from southern Wisconsin and extreme eastern Iowa
   into parts of northern and central Illinois.  A tornado threat
   cannot be ruled out, mainly in southern Wisconsin.  However, the
   limited potential for severe storm coverage is expected to preclude
   the need for a watch.

   DISCUSSION...Late afternoon surface analysis showed an area of low
   pressure centered in southwest WI with a cold front trailing to the
   south-southwest through extreme eastern IA to northwest to western
   MO, while a warm front extended east through southern WI into
   central Lower MI.  Objective analyses through the late afternoon
   indicated the environment in the wake of earlier convection and east
   of the cold front across southern WI and northern/central IL has
   destabilized some, despite weak midlevel lapse rates, with MLCAPE of
   1000-1500 J/kg.

   Stronger forcing for ascent (attendant to a progressive upper MS
   Valley shortwave trough) appears to be spreading across the cold
   front and warm sector, at this time, per water vapor imagery with a
   band of 40-50 kt westerly 500-mb winds per area VAD data across
   WI/northern IL.  Although storms have developed along the cold
   front, weak midlevel lapse rates and veered low-level winds appear
   to be limiting the coverage thus far of stronger/sustained storms. 
   Although effective bulk shear of 30-40 kt suggests organized storms
   will be possible as the cold front and shortwave trough advance east
   this evening, veered low-level winds should continue to limit
   convergence and greater coverage of storms along the cold front.   

   The tornado threat appears to be greatest with any storms that
   interact with the warm front, where low-level shear is the greatest.
   Stronger surface vorticity and surface-3 km MLCAPE of 100-125 J/kg,
   objectively analyzed in vicinity of the lake breeze in northeast IL
   to southeast WI, suggest an isolated tornado threat cannot be ruled
   out.  Despite the tornado potential, the coverage of storms is
   expected to remain limited through the evening.

   ..Peters/Grams.. 08/03/2017

   ...Please see for graphic product...


   LAT...LON   40319041 40729102 40909124 41879094 42979036 43868996
               43888933 43668799 42498786 40948820 40388859 40048951

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