MESOSCALE DISCUSSION 0478
   NWS STORM PREDICTION CENTER NORMAN OK
   0747 PM CDT TUE APR 19 2011
   
   AREAS AFFECTED...NERN TX...EXTREME SERN OK...WRN AND CNTRL AR
   
   CONCERNING...TORNADO WATCH 155...
   
   VALID 200047Z - 200215Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 155 CONTINUES.
   
   THREAT FOR MAINLY ISOLATED LARGE HAIL...DAMAGING WIND AND PERHAPS A
   COUPLE OF ISOLATED TORNADOES WILL PERSIST NEXT FEW HOURS FROM NERN
   TX...EXTREME SERN OK INTO WRN AR. STORMS COULD DEVELOP A LITTLE
   FARTHER SWD INTO EXTREME SRN AR.
   
   COLD FRONT EXTENDS FROM SRN MO SWWD THROUGH NWRN AR...SERN OK INTO
   N-CNTRL TX WHERE IT INTERSECTS DRYLINE EAST OF STEPHENVILLE. THE
   DRYLINE EXTENDS SWD TO EAST OF DEL RIO. ISOLATED STORMS CONTINUE
   DEVELOPING NEAR TRIPLE POINT AND NEWD ALONG AND AHEAD OF THE COLD
   FRONT THROUGH WRN AND CNTRL AR. DEEP VERTICAL SHEAR FROM 35-40
   KT...STEEP LAPSE RATES AND 3000+ MLCAPE REMAIN SUPPORTIVE OF
   SUPERCELLS WITH VERY LARGE HAIL. ISOLATED TORNADOES REMAIN POSSIBLE
   NEXT COUPLE HOURS...BUT MODEST 0-1 KM STORM RELATIVE HELICITY IS NOT
   EXPECTED TO UNDERGO A SIGNIFICANT INCREASE GIVEN PRIMARY LOW LEVEL
   JET STRENGTHENING WELL EAST OF THIS REGION. THIS IN CONJUNCTION WITH
   A STABILIZING BOUNDARY LAYER SHOULD REMAIN LIMITING FACTORS FOR A
   MORE ROBUST TORNADO THREAT IN WW 155.
   
   OVERALL COVERAGE OF STORMS IN NERN TX HAS DIMINISHED...BUT STORMS
   MAY CONTINUE DEVELOPING SWD ALONG THE DRYLINE-COLD FRONT MERGER.
   STORMS MAY ALSO BE MORE PERSISTENT ACROSS AR WHERE INFLUENCE OF
   DEEPER ASCENT ATTENDING SHORTWAVE TROUGH APPEARS TO BE WEAKENING THE
   CAPPING INVERSION.
   
   ..DIAL.. 04/20/2011
   
   
   ATTN...WFO...LZK...SHV...TSA...FWD...
   
   LAT...LON   34749478 36169335 36379266 36039202 34689312 33019422
               32439540 32389708 34749478