MESOSCALE DISCUSSION 0273
   NWS STORM PREDICTION CENTER NORMAN OK
   1058 PM CDT SUN MAR 17 2013
   
   AREAS AFFECTED...SRN THROUGH CNTRL AND ERN AR INTO NWRN MS AND WRN
   TN
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 180358Z - 180630Z
   
   PROBABILITY OF WATCH ISSUANCE...40 PERCENT
   
   SUMMARY...STORMS ARE EXPECTED TO UNDERGO A GRADUAL INCREASE IN
   COVERAGE AND INTENSITY FROM SRN THROUGH CNTRL AND ERN AR INTO NWRN
   MS AND WRN TN NEXT SEVERAL HOURS. ISOLATED LARGE HAIL AND DAMAGING
   WIND WILL BE THE MAIN THREATS...THOUGH A TORNADO OR TWO CANNOT BE
   RULED OUT FROM SRN AR INTO NWRN MS AND SWRN TN. WW IS POSSIBLE...BUT
   ISSUANCE WILL ULTIMATELY DEPEND ON CONVECTIVE TRENDS.
   
   DISCUSSION...LATE THIS EVENING A QUASI-STATIONARY FRONT EXTENDS FROM
   THE TN VALLEY SWWD THROUGH WRN TN...ERN AND SRN AR INTO NERN TX.
   DEWPOINTS NEAR 60 HAVE ADVECTED THROUGH THE WARM SECTOR BENEATH A
   WARM EML RESULTING IN 500-1000 J/KG SBCAPE ALONG AND SOUTH OF THE
   BOUNDARY. AN AXIS OF HIGHER THETA-E AIR WITH UPPER 50S DEWPOINTS
   HAVE ALSO ADVECTED ABOVE THE STABLE SURFACE LAYER NORTH OF THE FRONT
   RESULTING IN 1000-1500 J/KG MUCAPE AS INDICATED ON THE 00Z RAOB FROM
   LITTLE ROCK AR. 
   
   A STOUT INVERSION ASSOCIATED WITH ERN EXTENSION OF THE EML HAS SO
   FAR INHIBITED DEVELOPMENT OF DEEP CONVECTION...BUT WV IMAGERY SHOWS
   A SHORTWAVE TROUGH MOVING THROUGH OK AND NRN TX. AS LEADING EDGE OF
   MID LEVEL ASCENT ACCOMPANYING THIS FEATURE BEGINS TO OVERTAKE
   INSTABILITY AXIS...THE INVERSION SHOULD WEAKEN AND PROMOTING AN
   INCREASE IN STORMS NEAR AND NORTH OF THE QUASISTATIONARY FRONT
   TONIGHT. TRENDS IN RADAR IMAGERY AND LIGHTNING DATA INDICATE
   CONVECTION IS ALREADY BEGINNING TO DEEPEN AND SLOWLY INTENSIFY OVER
   SERN AR/NWRN MS. STRONG EFFECTIVE SHEAR AND STEEP MID LEVEL LAPSE
   RATES WILL SUPPORT POTENTIAL FOR UPDRAFT ROTATION AND A THREAT OF
   LARGE HAIL. SOME OF THE STORMS DEVELOPING NEAR THE FRONT MAY ALSO
   POSE A THREAT FOR ISOLATED DAMAGING WIND. LARGE HODOGRAPHS EXIST IN
   VICINITY OF FRONT FROM ERN AR INTO NWRN MS AND WRN TN...SUGGESTING A
   THREAT FOR A COUPLE OF TORNADOES. HOWEVER...A NEAR SFC BASED
   INVERSION LIKELY EXISTS IN THIS AREA BASED ON CURRENT WARM SECTOR
   TEMPERATURES AND DEWPOINTS...INDICATING ACTIVITY IS PROBABLY
   SLIGHTLY ELEVATED.
   
   ..DIAL/THOMPSON.. 03/18/2013
   
   
   ATTN...WFO...MEG...JAN...LZK...SHV...
   
   LAT...LON   36048922 34838940 33219233 33159390 33809373 35719124
               36048922