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Mesoscale Discussion 521
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   Mesoscale Discussion 0521
   NWS Storm Prediction Center Norman OK
   0655 PM CDT Wed Apr 19 2017

   Areas affected...Northern/Central Iowa

   Concerning...Severe potential...Watch possible 

   Valid 192355Z - 200130Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Thunderstorms are expected to increase in areal coverage
   across much of central and northern Iowa over the next few hours. 
   Marginally severe hail is the primary risk with convection north of
   the warm front.

   DISCUSSION...Low-level warm advection should aid areal expansion of
   convection across much of central and northern IA over the next few
   hours.  Latest surface analysis suggests the primary warm front has
   advanced into southern Crawford/Carroll counties, just north of
   current Tornado Watch 148.  A marked increase in thunderstorm
   activity has been noted along the cold front extending from
   northwest IA into southeast NE.  Activity north of I-80 has yet to
   exhibit very large hail, possibly due to unfavorable storm mode and
   significant clustering.  Unless discrete supercells evolve near the
   warm front it appears much of the elevated convection may struggle
   to generate large hail.  For these reasons will continue to monitor
   for possible ww.

   ..Darrow/Edwards.. 04/19/2017

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

   ATTN...WFO...ARX...MPX...DMX...FSD...OAX...

   LAT...LON   41959583 43379452 43549296 43019257 41999348 41959583 

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