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Mesoscale Discussion 1620
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   MESOSCALE DISCUSSION 1620
   NWS STORM PREDICTION CENTER NORMAN OK
   0934 AM CDT TUE AUG 26 2014

   AREAS AFFECTED...PORTIONS OF NRN IL...NWRN INDIANA...SERN WI

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 261434Z - 261630Z

   PROBABILITY OF WATCH ISSUANCE...20 PERCENT

   SUMMARY...THUNDERSTORMS CROSSING THE REGION THIS MORNING COULD
   PRODUCE ISOLATED MARGINALLY SVR WIND/HAIL. WHILE CONVECTIVE TRENDS
   WILL CONTINUE TO BE MONITORED...WW ISSUANCE IS CURRENTLY UNLIKELY.

   DISCUSSION...THE REMNANTS OF NOCTURNAL CONVECTION THAT EVOLVED FROM
   ERN NEB TO IA HAVE CROSSED THE MS RIVER...PRESENTLY REACHING A LINE
   FROM ROCKFORD TO MOLINE. CAPPI DATA AT 9 KM INDICATE SUSTENANCE OF
   ONGOING MULTICELL CLUSTERS...WHICH ARE APPROACHING A SFC BOUNDARY
   DRAPED FROM THE CHICAGO AREA INTO W-CNTRL IL. THE 12Z ILX RAOB AND
   SFC OBSERVATIONS SUGGEST RICH BOUNDARY-LAYER MOISTURE IN PROXIMITY
   TO AND ON THE WARM SIDE OF THIS BOUNDARY -- E.G. LOWEST-100-MB MEAN
   MIXING RATIO AROUND 16 G/KG. DIURNAL HEATING OF THIS MOISTURE WILL
   BOOST BUOYANCY...WITH MLCAPE LIKELY REACHING 1500-2500 J/KG DURING
   THE NEXT FEW HOURS.

   ONGOING MULTICELL CLUSTERS WILL APPROACH/CROSS THE BOUNDARY --
   INCLUDING THE CHICAGO AREA IN THE 1545-1700Z TIME FRAME -- AND A
   RISK FOR INTENSE UPDRAFTS/DOWNDRAFTS WILL EXIST. LOT AND MKX VWPS
   SAMPLE 25-30 KT WLYS IN THE 1-4-KM LAYER...WHICH WILL BOLSTER
   CONVECTIVE MOMENTUM TRANSPORT TO POTENTIALLY YIELD ISOLATED DMGG
   WIND GUSTS. ISOLATED MARGINALLY SVR HAIL CANNOT BE RULED OUT.
   HOWEVER...ONLY MODEST MID-LEVEL FLOW/DEEP SHEAR YIELD UNCERTAINTY IN
   A MORE ORGANIZED...SUSTAINED SVR RISK. NEVERTHELESS...CONVECTIVE
   TRENDS WILL CONTINUE TO BE MONITORED.

   ..COHEN/MEAD.. 08/26/2014


   ATTN...WFO...LOT...MKX...DVN...

   LAT...LON   42718878 42768753 41468694 40878805 41458932 42718878 

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Page last modified: August 26, 2014
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