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Mesoscale Discussion 1084
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   MESOSCALE DISCUSSION 1084
   NWS STORM PREDICTION CENTER NORMAN OK
   1248 PM CDT SAT JUN 20 2015

   AREAS AFFECTED...MUCH OF IOWA AND NORTHWESTERN ILLINOIS

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 201748Z - 201945Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...STRONG TO SEVERE STORMS WITH MARGINALLY SEVERE MAY PERSIST
   THIS AFTERNOON...AND A GREATER THREAT OF SEVERE MAY EMERGE LATER
   THIS AFTERNOON ESPECIALLY ACROSS CENTRAL/SOUTHERN IOWA. A WW WILL
   LIKELY NOT BE NEEDED IN THE SHORT-TERM...BUT TRENDS WILL BE
   MONITORED FOR A POTENTIAL INCREASING THREAT LATER THIS
   AFTERNOON/EVENING.

   DISCUSSION...STORMS ONGOING ACROSS CENTRAL AND EASTERN IOWA HAVE
   BEEN MARGINALLY SEVERE WITH OCCASIONAL REPORTS OF 1 INCH HAIL
   REPORTED WITHIN THE LAST TWO HOURS.  THESE STORMS ARE CURRENTLY
   ELEVATED ATOP A SHALLOW LAYER OF RAIN-COOLED AIR LEFT BEHIND FROM
   PREVIOUS MORNING CONVECTION.  THIS CONVECTION IS EXPECTED TO
   CONTINUE THROUGHOUT THE DAY...FORCED BY SUSTAINED CONVERGENCE AROUND
   850 MB AND A FAVORABLE THERMODYNAMIC PROFILE WITH SUFFICIENT
   MID-LEVEL INSTABILITY.  OCCASIONAL LARGE HAIL WILL CONTINUE TO BE
   THE MAIN THREAT WITH STRONGER CELLS...BUT THE MARGINALITY AND
   SPORADIC NATURE OF THE THREAT WILL LIKELY PRECLUDE A WW ISSUANCE FOR
   THIS ACTIVITY IN THE SHORT TERM. 

   LATER THIS AFTERNOON...MODEL GUIDANCE AND OBSERVATIONS SUGGEST THE
   POSSIBILITY OF MORE SURFACE-BASED STORMS DEVELOPING ALONG A COLD
   FRONT ENTERING NORTHWESTERN IOWA...WITH DEVELOPMENT ALSO POSSIBLE
   ALONG A DIFFERENTIAL HEATING/OUTFLOW BOUNDARY INTERSECTING THAT
   FRONT FROM NEAR SPW TO NEAR DSM TO NEAR BRL.  LOW-LEVEL SHEAR NEAR
   AND NORTH/EAST OF THIS BOUNDARY IS HIGHER DUE TO BACKED LOW-LEVEL
   WINDS...AND ALTHOUGH CURRENT CONVECTION IS LIKELY NOT REALIZING THE
   ENHANCED SHEAR DUE TO THEIR ELEVATED NATURE...ANY SURFACE BASED
   ACTIVITY THAT DEVELOPS LATER THIS AFTERNOON MAY REALIZE THE
   INCREASED LOW-LEVEL SHEAR WHILE ALSO FORMING IN A STRONGLY UNSTABLE
   ENVIRONMENT...POSING A GREATER SEVERE THREAT.  WW ISSUANCE MAY BE
   NEEDED LATER ONCE THE DETAILS OF THIS POTENTIAL ACTIVITY BECOME
   CLEARER LATER THIS AFTERNOON.

   ..COOK/GUYER.. 06/20/2015


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

   LAT...LON   41319319 41399371 41429429 41419504 41579572 41929600
               42399595 42679561 42849491 43219365 43199238 42919131
               42519044 42108996 41478968 40848970 40549046 40729124
               41069188 41319319 

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Page last modified: June 20, 2015
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