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Mesoscale Discussion 420
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   MESOSCALE DISCUSSION 0420
   NWS STORM PREDICTION CENTER NORMAN OK
   1225 PM CDT SUN APR 27 2014

   AREAS AFFECTED...ERN OK...NERN TX THROUGH WRN AND CNTRL ARKANSAS

   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   VALID 271725Z - 271930Z

   PROBABILITY OF WATCH ISSUANCE...95 PERCENT

   SUMMARY...THE ATMOSPHERE IS EXPECTED TO BECOME INCREASINGLY
   FAVORABLE FOR LONG TRACK SUPERCELLS CAPABLE OF TORNADOES...A FEW OF
   WHICH COULD BE STRONG BY MID-LATE AFTERNOON. LARGE HAIL AND DAMAGING
   WIND WILL ALSO BECOME LIKELY WITH THE STRONGER STORMS. MESOSCALE AND
   CONVECTIVE TRENDS WILL CONTINUE TO BE MONITORED...AND A TORNADO
   WATCH WILL LIKELY BE NEEDED BY 19Z-20Z.

   DISCUSSION...EARLY THIS AFTERNOON A PACIFIC COLD FRONT EXTENDS FROM
   ERN KS SWD THROUGH CNTRL OK INTO NCNTRL TX. A WARM FRONT WAS LOCATED
   FROM NRN MS THROUGH CNTRL ARKANSAS. THE WARM SECTOR BETWEEN THESE
   BOUNDARIES CONTINUES TO DESTABILIZE AS A STRONG LLJ ADVECTS UPPER
   60S DEWPOINTS NWD BENEATH STEEP LAPSE RATES. HOWEVER...THE RATE OF
   BOUNDARY LAYER DESTABILIZATION HAS BEEN SLOWED BY MULTILAYER CLOUDS
   INCLUDING STRATUS AND CONVECTIVE DEBRIS. LATEST VISIBLE IMAGERY DOES
   SHOW NUMEROUS CLOUD BREAKS...AND THE STRATUS DECK OVER CENTRAL
   ARKANSAS MAY EVENTUALLY ERODE FROM THE SOUTH. AN AXIS OF 1500-2500
   J/KG MLCAPE WILL DEVELOP ACROSS THIS REGION THIS AFTERNOON.

   A PRE-FRONTAL BELT OF ASCENT WITH WHAT APPEARS TO BE AN EWD
   PROPAGATING GRAVITY WAVE CONTINUES FROM WRN ARKANSAS THROUGH NWRN
   TX. MEANWHILE AN UPPER JET STREAK ROTATING THROUGH BASE OF THE UPPER
   TROUGH WILL SHIFT EWD THROUGH NRN TX INTO THE LOWER MS VALLEY.
   FORCING FOR ASCENT ASSOCIATED WITH THESE FEATURES AS WELL AS
   BOUNDARY LAYER WARMING SHOULD EVENTUALLY WEAKEN THE CAP SUFFICIENTLY
   FOR SURFACE BASED THUNDERSTORM DEVELOPMENT WITHIN AXIS OF
   PRE-FRONTAL CONFLUENCE IN WARM SECTOR...AS WELL AS ALONG THE PACIFIC
   FRONT. STRENGTHENING WIND PROFILES ASSOCIATED WITH THE APPROACHING
   UPPER JET AND FAVORABLE LOW-LEVEL HODOGRAPHS WILL SUPPORT SUPERCELLS
   WITH LOW-LEVEL MESOCYCLONES CAPABLE OF PRODUCING TORNADOES AND LARGE
   HAIL. THE 0-1 KM HODOGRAPHS APPEAR MAXIMIZED ACROSS CNTRL AR WHERE
   LOW-LEVEL WINDS REMAIN BACKED IN VICINITY OF THE WARM FRONT THAT IS
   CURRENTLY BEING REINFORCED BY ELEVATED CONVECTION.

   ..DIAL/THOMPSON.. 04/27/2014


   ATTN...WFO...LZK...SHV...TSA...

   LAT...LON   34059531 35869495 35829294 34869170 33779184 32549318
               32559460 34059531 

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Page last modified: April 27, 2014
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