Mesoscale Discussion 1522
   NWS Storm Prediction Center Norman OK
   0254 PM CDT Fri Aug 18 2017

   Areas affected...Northeast South Dakota...Southwest
   Minnesota...Northwest Iowa

   Concerning...Severe potential...Watch possible 

   Valid 181954Z - 182230Z

   Probability of Watch Issuance...40 percent

   SUMMARY...A threat for isolated large hail and wind damage should
   continue to develop this afternoon from northeast South Dakota
   southeastward into southwestern Minnesota. Weather watch issuance
   will need to be considered.

   DISCUSSION...The latest surface analysis shows a cold front moving
   eastward across eastern South Dakota with surface dewpoints just
   ahead of the front in the mid 60s F. In response to the low-level
   moisture and surface heating, moderate instability has developed
   with MLCAPE values estimated in the 1000 to 1500 J/kg range. In
   addition, water vapor imagery shows an upper-level trough over the
   upper Mississippi Valley with a cold pocket aloft where 500 mb
   temperatures are in the -14 to -15 C range. This combined with
   strong large-scale ascent associated with the upper-level trough and
   increasing instability, will be favorable for an isolated severe
   threat this afternoon. Although deep-layer shear is not that strong,
   the cold temperatures aloft will be favorable for hail with the
   stronger updrafts. As cells continue to move southeastward into
   stronger instability and more favorable deep-layer shear, a wind
   damage threat may also develop.

   ..Broyles/Goss.. 08/18/2017

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

   ATTN...WFO...MPX...DMX...FSD...OAX...ABR...

   LAT...LON   45549572 45749715 45089740 44629735 43169672 41919541
               42219398 43469354 44439430 45549572