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Mesoscale Discussion 338
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   MESOSCALE DISCUSSION 0338
   NWS STORM PREDICTION CENTER NORMAN OK
   0234 PM CDT SUN APR 13 2014

   AREAS AFFECTED...EASTERN TEXAS...NORTHWESTERN LOUISIANA...SOUTHWEST
   ARKANSAS

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 131934Z - 132200Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...ONGOING THUNDERSTORMS MAY BEGIN TO INTENSIFY DURING THE
   AFTERNOON AND EVENING HOURS. IF THIS INTENSIFICATION OCCURS...LARGE
   HAIL...DAMAGING WINDS...AND TORNADOES WILL BE POSSIBLE.

   DISCUSSION...THUNDERSTORMS ARE ONGOING WITHIN AN ELEVATED MOIST
   PLUME ACROSS EASTERN TEXAS AND SOUTHEAST OKLAHOMA. MORNING SOUNDINGS
   SUGGEST THESE THUNDERSTORMS HAVE BEEN ELEVATED IN
   NATURE...ORIGINATING ABOVE A STRONG LOW-LEVEL INVERSION CENTERED
   BETWEEN 850MB AND 700MB. GIVEN THE INCREASING ASCENT OVERSPREADING
   THE AREA...AND MOISTENING OF THE LOW-LEVELS...A GRADUAL TRANSITION
   TO SURFACE BASED CONVECTION WILL BE POSSIBLE OVER THE NEXT FEW
   HOURS. 

   THE ENVIRONMENT AHEAD OF THE ONGOING THUNDERSTORMS IS UNDERGOING
   DESTABILIZATION AS INDICATED BY THE INCREASE IN SBCAPE/MUCAPE TO
   BETWEEN 500-1000 J/KG. OVER THE NEXT FEW HOURS...DEEP LAYER SHEAR IS
   EXPECTED TO INCREASE TO ALMOST 50 KTS AS A MID-LEVEL JET STREAK
   OVERSPREADS THE AREA. THE COMBINATION OF INSTABILITY/SHEAR WOULD
   SUPPORT SEVERE THUNDERSTORMS CAPABLE OF LARGE HAIL AND DAMAGING
   WINDS. IF ONGOING CONVECTION CAN TRANSITION TO A MORE
   DISCRETE...SURFACE BASED MODE...OR...IF DEVELOPING CONVECTION AHEAD
   OF THE LINE CAN SUSTAIN ITSELF...EFFECTIVE STORM-RELATIVE HELICITY
   VALUES AROUND 300 M2/S2 WOULD ALSO SUPPORT A TORNADO THREAT.

   IF A TRANSITION TO SURFACE BASED CONVECTION BECOMES APPARENT...A
   WATCH MAY BECOME NECESSARY.

   ..MARSH/HART.. 04/13/2014


   ATTN...WFO...LZK...SHV...HGX...FWD...

   LAT...LON   31399732 32129650 32749577 33329521 33869481 34379427
               33899310 33059274 32099329 31569394 31189504 31079654
               31399732 

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Page last modified: April 13, 2014
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