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Mesoscale Discussion 676
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   MESOSCALE DISCUSSION 0676
   NWS STORM PREDICTION CENTER NORMAN OK
   0219 PM CDT SAT MAY 18 2013
   
   AREAS AFFECTED...SWRN KS...WRN OK...NW TX...FAR ERN OK/TX PANHANDLES
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 181919Z - 182015Z
   
   PROBABILITY OF WATCH ISSUANCE...95 PERCENT
   
   SUMMARY...SCATTERED TSTM INITIATION IS EXPECTED ON THE DRYLINE BY
   21-22Z. VERY LARGE HAIL...ISOLATED TORNADOES...AND DAMAGING WIND
   WILL BE POSSIBLE. WATCH ISSUANCE IS EXPECTED IN THE NEXT HOUR OR SO.
   
   DISCUSSION...LATEST SFC ANALYSIS DEPICTS THE DRYLINE EXTENDING FROM
   SWRN KS INTO THE FAR ERN OK/TX PANHANDLES AND NW TX. VIS IMAGERY
   SHOWS CU INCREASING IN THE WELL-MIXED AIRMASS IN THE VICINITY OF THE
   DRYLINE ACROSS SW KS INTO THE TX PANHANDLE. WHILE ONE EMBEDDED VORT
   MAX IS MOVING NWD OUT OF THE AREA...ANOTHER EMBEDDED VORT MAX OVER
   SERN CO/NERN NM SHOULD AID IN CONVECTIVE INITIATION LATER THIS
   AFTERNOON. 
   
   THE 18Z DDC SOUNDING SHOWS VERY STEEP LAPSE RATES IN EXCESS OF 9.5
   C/KM IN THE 750-500 MB LAYER...WHICH WILL SUPPORT VERY HIGH TO
   EXTREME MLCAPE OF 3000-4000 J/KG IN AREAS AHEAD OF THE DRYLINE THIS
   AFTERNOON AND EARLY EVENING. WHILE FLOW IS RELATIVELY
   MODEST...INCREASING SWLY MIDLEVEL FLOW IS SUPPORTING EFFECTIVE SHEAR
   OF 35-45 KTS AHEAD OF THE DRYLINE...WHICH WILL BE MORE THAN
   SUFFICIENT FOR SUPERCELL DEVELOPMENT UPON STORM INITIATION. 
   
   DISCRETE SUPERCELL ACTIVITY IS EXPECTED WITHIN THE FIRST 2-3 HOURS
   OF INITIATION...WITH VERY LARGE HAIL IN EXCESS OF BASEBALL SIZE THE
   PRIMARY THREAT. LARGE T/TD SPREADS AND RELATIVELY WEAK LOW-LEVEL
   SHEAR WILL LIMIT THE TORNADO THREAT INITIALLY...BUT A MARKED
   INCREASE IN THE LOW-LEVEL JET WILL INCREASE THE TORNADO THREAT
   TOWARD EVENING ACROSS MAINLY NWRN OK INTO SWRN KS...WITH ISOLATED
   STRONG TORNADOES POSSIBLE WITH ANY STORMS THAT CAN REMAIN DISCRETE
   AFTER 00Z. HOWEVER...STORM CONSOLIDATION IN A WELL-MIXED ENVIRONMENT
   MAY RESULT IN UPSCALE GROWTH AND A TRANSITION TO MORE OF A SEVERE
   WIND THREAT THIS EVENING...POSSIBLY LIMITING THE WINDOW OF
   OPPORTUNITY FOR A MORE ROBUST TORNADO THREAT.
   
   ..DEAN/KERR.. 05/18/2013
   
   
   ATTN...WFO...ICT...FWD...OUN...DDC...SJT...GLD...LUB...AMA...
   
   LAT...LON   37290112 37880150 38500134 38920033 38829937 38509866
               38129815 37669781 36889765 35559772 34699766 33459786
               32919805 32419816 32199830 31989879 31989936 32069993
               32170043 32790063 33780057 35300063 36140066 37290112 
   
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