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Mesoscale Discussion 1725
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   MESOSCALE DISCUSSION 1725
   NWS STORM PREDICTION CENTER NORMAN OK
   0133 AM CDT WED SEP 21 2016

   AREAS AFFECTED...SERN MINNESOTA...NERN IOWA PARTS OF SWRN AND
   CENTRAL WISCONSIN

   CONCERNING...SEVERE THUNDERSTORM WATCH 486...

   VALID 210633Z - 210830Z

   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 486
   CONTINUES.

   SUMMARY...A MOSTLY MARGINAL SEVERE HAIL/WIND THREAT MAY CONTINUE
   WITH STRONGER STORMS ACROSS SOUTHEASTERN MINNESOTA/SOUTHWESTERN
   WISCONSIN...GENERALLY WEST OF LA CROSS THROUGH THE LA CROSSE
   AREA...FOR ANOTHER COUPLE OF HOURS.  IT APPEARS UNLIKELY THAT A NEW
   WATCH WILL BE NEEDED...BUT IT IS POSSIBLE THAT PORTIONS OF WATCH 486
   COULD BE LOCALLY EXTENDED IN TIME/AREA.

   DISCUSSION...A WEAK MID-LEVEL WAVE ON THE SOUTHERN FRINGE OF THE
   STRONGER MID-LATITUDE WESTERLIES IS NOW CROSSING THE UPPER
   MIDWEST...AND LIKELY WILL CONTINUE EASTWARD TOWARD THE GREAT LAKES
   REGION THROUGH DAYBREAK.  AS THIS OCCURS...THE LATEST RAPID REFRESH
   SUGGESTS THAT A BRANCH OF STRONGER WEST SOUTHWESTERLY 850 MB FLOW
   EMANATING FROM THE MID MISSOURI VALLEY WILL GRADUALLY WEAKEN /FROM
   CURRENT 35-40 KT/ ACROSS SOUTHEASTERN MINNESOTA/ADJACENT
   NORTHEASTERN IOWA INTO SOUTHERN WISCONSIN.  DIMINISHING INFLOW OF
   AIR CHARACTERIZED BY MODERATE CAPE SEEMS LIKELY TO LEAD TO WEAKENING
   CONVECTIVE INTENSITY.

   UNTIL THIS OCCURS...THE RISK FOR SEVERE HAIL MAY CONTINUE ANOTHER
   COUPLE OF HOURS...MAINLY WITH CELLS ON THE SOUTHWESTERN FLANK OF THE
   EVOLVING CLUSTER OF STORMS...IN CLOSEST PROXIMITY TO THE SURFACE
   WARM FRONTAL ZONE.  EVEN THOUGH ACTIVITY IS GENERALLY ROOTED ABOVE A
   STABLE SURFACE-BASED LAYER...THIS LAYER APPEARS SHALLOW
   ENOUGH...COUPLED WITH AN INITIALLY DRY SUB-CLOUD LAYER... TO ALLOW
   FOR DOWNWARD MOMENTUM TRANSFER TO CONTRIBUTE TO SURFACE GUSTS
   OCCASIONALLY APPROACHING SEVERE LIMITS.  THIS THREAT APPEARS
   GREATEST NEAR THE CORE OF THE STRONGER 850 MB FLOW EXPECTED TO
   PROPAGATE ACROSS THE LA CROSSE AREA DURING THE NEXT COUPLE OF HOURS.

   ..KERR.. 09/21/2016


   ATTN...WFO...GRB...MKX...ARX...MPX...

   LAT...LON   44429464 45099252 44839046 44138928 43468859 42868956
               43139103 43299228 43949431 44429464 

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Page last modified: September 21, 2016
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