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Mesoscale Discussion 468
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   MESOSCALE DISCUSSION 0468
   NWS STORM PREDICTION CENTER NORMAN OK
   0254 PM CDT SUN APR 26 2015

   AREAS AFFECTED...PORTIONS W-CENTRAL/NW TX.

   CONCERNING...TORNADO WATCH 119...

   VALID 261954Z - 262200Z

   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 119 CONTINUES.

   SUMMARY...CONTINUE WW.  SEVERAL SUPERCELLS CAPABLE OF DAMAGING HAIL
   AND A TORNADO OR TWO HAVE FORMED OVER WRN PORTIONS WW AND WILL MOVE
   ENEWD TO NEWD ACROSS WW AREA OVER NEXT FEW HOURS.  SOME UPSCALE
   EVOLUTION INTO CLUSTERED/SMALL-MCS MODE IS PSBL. 
   ADDITIONAL SVR DEVELOPMENT MAY OCCUR FROM SRN PORTIONS WW INTO ERN
   EDWARDS PLATEAU/WRN HILL COUNTRY.  CONVECTIVE/DESTABILIZATION TRENDS
   WILL BE MONITORED FOR PSBL NEW WW THERE.

   DISCUSSION...SFC MESOANALYSIS SHOWS DRYLINE INTERSECTING
   WAVY/QUASISTATIONARY FRONTAL ZONE NEAR SWRN CORNER OF COTTLE
   COUNTY...AND EXTENDING SWD BETWEEN SNK-SWW TO NEAR SOA.  FRONT
   EXTENDS EWD ACROSS SRN OK NEAR OR JUST N OF NRN EDGE OF WW. 
   CONFLUENCE LINE WAS DRAWN COTTLE COUNTY SSEWD TO NEAR JCT.  DRYLINE
   SHOULD CONTINUE MIXING EWD TO POSITION NEAR CONFLUENCE LINE BEFORE
   STALLING LATE THIS AFTN...PRIOR TO ARRIVAL OF PAC COLD FRONT NOW
   OVER WRN PORTIONS SOUTH PLAINS AND PERMIAN BASIN REGIONS. 

   DIFFERENTIAL-HEATING/OUTFLOW BOUNDARY FROM EARLIER/ELEVATED
   CONVECTION WAS DRAWN FROM WILLIAMSON COUNTY NWWD INTO SUPERCELL
   APCHG BROWN/CALLAHAN COUNTY LINE...AND MAY EXTEND FARTHER NW TOWARD
   TOWARD SUPERCELL APCHG NRN SHACKLEFORD COUNTY.  THIS BOUNDARY WAS
   MOVING NEWD ABOUT 15-20 KT...POTENTIALLY ALLOWING SUPERCELLS TO HAVE
   LONG RESIDENCE TIME WITH THIS BOUNDARY.    ASSOCIATED LOW-LEVEL
   VORTICITY MAY ENHANCE MESOCYCLONE STRENGTH/TORNADO POTENTIAL FOR
   THOSE STORMS OR ANY OTHERS THAT CAN INTERACT WITH IT.  

   SMALL POCKET OF STG SFC DRYING WAS EVIDENT AT BKD AND TO LESSER
   EXTENT RPH...LIKELY RELATED TO DOWNDRAFTS FROM MIDLEVEL CONVECTION. 
   THIS AIR MAY BE ENTRAINED INTO INFLOW OF STORMS TO ITS W IN ANOTHER
   COUPLE HOURS...POTENTIALLY LEADING TO MESSIER STRUCTURES. 
   MEANWHILE...ADDITIONAL DEVELOPMENT ALSO IS POSSIBLE SW OF EXISTING
   CONVECTION ALONG BLENDING DRYLINE/CONFLUENCE LINE.   AS THIS
   OCCURS...ALONG WITH ADDITIONAL DIABATIC SFC HEATING S OF ONGOING
   CONVECTION...ASSOCIATED LIFT WILL INCREASE.  POTENTIAL THEREFORE
   EXISTS FOR AT LEAST ISOLATED SVR-TSTM DEVELOPMENT NEAR SRN EDGE OF
   WW AND SWD THROUGH HILL COUNTRY.  ANY SUCH CONVECTION MAY BECOME
   SUPERCELLULAR WITH LARGE/DAMAGING HAIL AND TORNADO RISK.

   --- NOTE ---
   RAP MODEL HAS HAD A SUBSTANTIAL DRYING/OVER-MIXING PROBLEM OVER MUCH
   OF CENTRAL TX AND SRN OK ALL DAY LONG.  THIS APPEARS TO BE STRONGLY
   AFFECTING MOISTURE FIELDS AND AUTOMATED ANALYSES OF PARAMETERS
   DEPENDENT ON MOISTURE.  USE BUOYANCY/MOISTURE/CONVECTIVE PROGS FROM
   RAP...RAP-DEPENDENT HRRR...AND SPC/SFCOA FIELDS...WITH GREAT
   CAUTION.

   ..EDWARDS.. 04/26/2015


   ATTN...WFO...FWD...OUN...EWX...SJT...LUB...

   LAT...LON   30610013 33120036 33960044 34219973 34149849 33849781
               32189782 30779870 30419962 30610013 

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