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Mesoscale Discussion 1908
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   MESOSCALE DISCUSSION 1908
   NWS STORM PREDICTION CENTER NORMAN OK
   0933 PM CDT THU SEP 06 2012
   
   AREAS AFFECTED...PORTIONS OF IA
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 070233Z - 070430Z
   
   PROBABILITY OF WATCH ISSUANCE...60 PERCENT
   
   SUMMARY...POTENTIAL FOR AT LEAST ISOLATED SEVERE HAIL/PERHAPS
   DAMAGING WINDS SHOULD CONTINUE TO INCREASE THROUGH LATE EVENING
   ACROSS NORTHWEST/CENTRAL IA. WHILE THE EXTENT/MAGNITUDE OF THE
   SEVERE POTENTIAL THIS EVENING INTO THE OVERNIGHT IS A BIT
   UNCERTAIN...DEVELOPMENTAL TRENDS WILL BE CLOSELY MONITORED FOR A
   POSSIBLE WATCH.
   
   DISCUSSION...MASS RESPONSE APPEARS TO BE QUICKLY OCCURRING ACROSS
   THE MIDDLE MO VALLEY/IA VICINITY OWING TO UPSTREAM HEIGHT FALLS
   JET/APPROACHING UPPER JET STREAK...WITH A RECENT /SINCE 0115Z/
   DEVELOPMENT AND QUICK INCREASE OF A STRONG/SEVERE TSTM ACROSS
   NORTHWEST IA. THIS ACTIVITY IS OCCURRING ATOP A DRY/STABLE BOUNDARY
   LAYER TO THE NORTH-NORTHEAST OF A SURFACE LOW/WARM FRONT. IN TANDEM
   WITH THE WARM FRONT...A MOIST INFLUX WILL CONTINUE TO OCCUR
   NEAR/ABOVE THE SURFACE...ALTHOUGH THE IMMEDIATE SOURCE REGION
   AIRMASS /AT LEAST INITIALLY/ IS NOT ROBUSTLY MOIST...REFERENCE 9
   G/KG MEAN MIXING RATIO PER THE 00Z OMAHA OBSERVED SOUNDING. 
   
   NONETHELESS...WITH AN INCREASING LOW LEVEL JET/DEEP LAYER FORCING
   FOR ASCENT...FACTORS SUCH AS THE AFOREMENTIONED MOIST INFLUX...EDGE
   OF THE ELEVATED MIXED LAYER...AND A STRONGLY SHEARED ENVIRONMENT MAY
   ACCOUNT FOR A SUSTENANCE/ADDITIONAL INTENSIFICATION OF THIS INITIAL
   DEVELOPMENT...WHILE LIKELY LEADING TO ADDITIONAL TSTMS BY LATE
   EVENING/OVERNIGHT ACROSS NORTHWEST/CENTRAL IA. AT LEAST AN
   ISOLATED/MARGINAL SEVERE HAIL THREAT WILL LIKELY BE THE PRIMARY
   HAZARD GIVEN THE ELEVATED NATURE OF THESE STORMS. HOWEVER...DAMAGING
   WINDS CANNOT BE DISCOUNTED LATER THIS EVENING/OVERNIGHT ESPECIALLY
   NEAR/JUST NORTHEAST OF THE WARM FRONT GIVEN STEADY LOW-LEVEL
   MOISTENING AND INCREASINGLY STRONG MEAN WESTERLY FLOW.
   
   ..GUYER/HART.. 09/07/2012
   
   
   ATTN...WFO...ARX...DMX...FSD...OAX...
   
   LAT...LON   42119579 43389589 43319362 42859257 41729291 41359342
               41519502 42119579 
   
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Page last modified: September 07, 2012
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