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Mesoscale Discussion 677
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   MESOSCALE DISCUSSION 0677
   NWS STORM PREDICTION CENTER NORMAN OK
   0331 PM CDT SAT MAY 18 2013
   
   AREAS AFFECTED...WRN/CNTRL SD...NERN WY
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 182031Z - 182130Z
   
   PROBABILITY OF WATCH ISSUANCE...40 PERCENT
   
   SUMMARY...TSTM COVERAGE IS EXPECTED TO INCREASE IN COVERAGE THROUGH
   THE REMAINDER OF THE AFTERNOON...WITH A PRIMARY THREAT OF LARGE HAIL
   AND DAMAGING WINDS. AREA IS BEING MONITORED FOR A POSSIBLE WW.
   
   DISCUSSION...SLOW-MOVING SUPERCELL THUNDERSTORMS HAVE BEEN ONGOING
   FOR THE LAST 1-2 HOURS ACROSS THE BLACK HILLS...WITH MODERATE MLCAPE
   OF 1000-2000 J/KG AND EFFECTIVE SHEAR OF 35-45 KTS SUPPORTING A
   LARGE HAIL RISK. ADDITIONAL ATTEMPTS AT INITIATION ARE UNDERWAY
   NORTH OF THE ONGOING SUPERCELLS...AND ALSO FURTHER EAST NEAR PIR
   ALONG A DIFFUSE SLOW-MOVING WARM FRONT. MULTIPLE EMBEDDED VORTICITY
   MAXIMA WITHIN BROAD SWLY MIDLEVEL FLOW WILL CONTINUE TO SUPPORT TSTM
   DEVELOPMENT...WITH SUFFICIENT INSTABILITY/SHEAR FOR ORGANIZED STORM
   STRUCTURES. 
   
   SPLITTING SUPERCELLS WILL BE THE PRIMARY MODE FOR THE NEXT 2-3
   HOURS...WITH A THREAT OF LARGE HAIL AND PERHAPS AN ISOLATED
   TORNADO...ESPECIALLY WITH ANY STORMS INTERACTING WITH THE WARM
   FRONT. UPSCALE GROWTH INTO ONE OR MORE CLUSTERS IS POSSIBLE EARLY
   THIS EVENING...WHICH WOULD LEAD TO INCREASE IN SEVERE WIND RISK. IF
   THE UPWARD TREND IN TSTM COVERAGE CONTINUES...WW ISSUANCE WILL BE
   POSSIBLE.
   
   ..DEAN/KERR.. 05/18/2013
   
   
   ATTN...WFO...FSD...ABR...UNR...CYS...BYZ...
   
   LAT...LON   43490430 44130510 45020508 45630337 45730190 45590035
               45139934 44469890 43909877 43549887 43369958 43100010
               43040042 43050199 43010293 43030356 43070388 43330414
               43490430 
   
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