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Mesoscale Discussion 1390
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   Mesoscale Discussion 1390
   NWS Storm Prediction Center Norman OK
   1123 PM CDT Fri Jul 21 2017

   Areas affected...Northeast IA...Southern WI...Northern
   IL...Northwest IN

   Concerning...Severe Thunderstorm Watch 429...

   Valid 220423Z - 220530Z

   The severe weather threat for Severe Thunderstorm Watch 429
   continues.

   SUMMARY...Strong thunderstorms will continue across northern and
   eastern portions of WW429 through the early morning hours. A local
   extension may be needed for the next few hours.

   DISCUSSION...Low-level warm advection appears to be partly
   responsible for recent increase in convection across northeast IA
   into northwest IL. Latest observational data and short-range models
   suggest LLJ is focused atop a pronounced outflow boundary that
   should move little over the next several hours. LLJ is expected to
   strengthen and veer toward northern IL and this should maintain a
   corridor of strong convection much of the night. While isolated
   large hail could be noted with this activity, unless it becomes
   clear that a damaging squall line or bow echo will evolve from this
   convection a new WW will not be issued; however, WW429 may be
   extended locally for the next few hours. Heavy rain may be the
   greatest risk through sunrise.

   ..Darrow.. 07/22/2017

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

   ATTN...WFO...IWX...GRR...IND...LOT...ILX...MKX...DVN...ARX...
   DMX...

   LAT...LON   42839367 42368620 40628620 41109367 42839367 

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