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Mesoscale Discussion 324
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   MESOSCALE DISCUSSION 0324
   NWS STORM PREDICTION CENTER NORMAN OK
   0230 PM CDT SAT APR 12 2014

   AREAS AFFECTED...IOWA INTO PARTS OF SRN WISCONSIN/NRN ILLINOIS

   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   VALID 121930Z - 122130Z

   PROBABILITY OF WATCH ISSUANCE...80 PERCENT

   SUMMARY...SEVERE STORM DEVELOPMENT APPEARS INCREASINGLY LIKELY
   ACROSS THE REGION DURING THE 22-00Z TIME FRAME.  LARGE HAIL MAY BE
   THE PRIMARY THREAT..AT LEAST FOR THE FIRST FEW HOURS...BUT SOME VERY
   LARGE HAIL IS POSSIBLE...AND A SEVERE THUNDERSTORM WATCH PROBABLY
   WILL BE ISSUED WITHIN THE NEXT HOUR OR SO.

   DISCUSSION...BENEATH THE NOSE OF WARM ELEVATED MIXED LAYER AIR
   ADVECTING EAST NORTHEAST OF THE CENTRAL PLAINS/MID MISSOURI VALLEY
   REGION...THE INCREASINGLY WELL MIXED AND DEEPENING BOUNDARY LAYER
   CONTINUES TO DESTABILIZE.  DESPITE SEASONABLY MODEST MOISTURE...WITH
   SURFACE DEW POINTS IN THE MID 50S...MAXIMUM MIXED LAYER CAPE APPEARS
   LIKELY TO EXCEED 2000 J/KG BY LATE AFTERNOON...IN THE PRESENCE OF
   RELATIVELY STEEP MID-LEVEL LAPSE RATES.

   A GRADUAL WEAKENING OF INHIBITION APPEARS UNDERWAY WITH CONTINUED
   INSOLATION...AND THIS APPEARS LIKELY TO BE AUGMENTED BY AT LEAST
   SUBTLE COOLING IN MID-LEVELS /AROUND 700 MB/ DURING THE NEXT FEW
   HOURS.  THE CONSENSUS OF MODEL GUIDANCE REMAINS SUGGESTIVE THAT THIS
   WILL LEAD TO INCREASING STORM DEVELOPMENT DURING THE 22-00Z TIME
   FRAME.

   THE LATEST HIGH RESOLUTION RAPID REFRESH OUTPUT...AT LEAST SOMEWHAT
   SUPPORTED BY OBSERVATIONAL DATA...SUGGEST ACTIVITY COULD INITIATE
   FIRST NEAR/SOUTH THROUGH EAST OF MASON CITY IA...IN THE VICINITY OF
   THE INTERSECTION OF A REMNANT CONVECTIVELY ENHANCED FRONTAL ZONE AND
   A LEE SURFACE TROUGH EXTENDING NORTHEASTWARD FROM THE CENTRAL
   PLAINS.  SUBSEQUENT DEVELOPMENT THEN APPEARS PROBABLE SOUTHWESTWARD
   ALONG THE TROUGH...TOWARD THE MID MISSOURI VALLEY.  

   ALTHOUGH LOW-LEVEL FLOW/SHEAR IS GENERALLY WEAK...DEEPER LAYER SHEAR
   BENEATH 30-50 KT WEST SOUTHWESTERLY 500 MB FLOW IS SUFFICIENT FOR
   ORGANIZED CONVECTION...INCLUDING SUPERCELLS.  AT LEAST FOR THE FIRST
   FEW HOURS...LARGE HAIL IS PROBABLY THE PRIMARY SEVERE THREAT...BUT
   IT DOES APPEAR THAT SOME OF THIS COULD BECOME RATHER SIZABLE...WITH
   LARGEST HAILSTONES POSSIBLY EXCEEDING 2 INCHES IN DIAMETER.

   ..KERR/HART.. 04/12/2014


   ATTN...WFO...MKX...DVN...ARX...DMX...FSD...OAX...

   LAT...LON   41999584 42899468 43429351 42818933 41829004 41039493
               41999584 

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Page last modified: April 12, 2014
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