MESOSCALE DISCUSSION 0675
   NWS STORM PREDICTION CENTER NORMAN OK
   1139 PM CDT SAT APR 30 2011
   
   AREAS AFFECTED...EXTREME NERN TX...EXTREME SERN OK AND ACROSS SWRN
   TO ERN AR
   
   CONCERNING...TORNADO WATCH 257...258...
   
   VALID 010439Z - 010545Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 257...258...CONTINUES.
   
   ALTHOUGH AN ISOLATED TORNADO CANNOT BE RULED OUT FROM EXTREME SWRN
   AR TO EAST CENTRAL-NERN AR...THE GREATEST THREAT HAS LIKELY
   TRANSITIONED TO HEAVY RAINFALL AS NEW STORMS HAVE DEVELOPED DURING
   THE LAST HOUR /SINCE 0315Z/ ACROSS FAR SERN OK /MCCURTAIN COUNTY/
   INTO SWRN AR /MONTGOMERY COUNTY/.  PRECIPITABLE WATER VALUES OF
   1.5-1.75 INCHES EXTENDING FROM ERN TX TO ERN AR AND THE LOWER TN
   VALLEY WILL SUPPORT RAINFALL RATES OF 1-2 INCH PER HOUR AS NEW
   STORMS CONTINUE TO DEVELOP OVER FAR SERN OK/SWRN AR AT THE NOSE OF A
   30-40 KT SSWLY LLJ.  THIS ACTIVITY IS EXPECTED TO CONTINUE TRAINING
   ENEWD OVERNIGHT AT 10-15 KT PER 00Z NAM PROPAGATION VECTORS WITH THE
   GREATEST THREAT PERSISTING IN A 40-50 MILE WIDE CORRIDOR FROM
   MCCURTAIN COUNTY OK TO WHITE COUNTY AR.
   
   LATE EVENING SURFACE ANALYSIS INDICATED A COLD FRONT EXTENDING FROM
   NWRN/WRN IL SSWWD TO SOUTH CENTRAL MO TO SWRN AR /25 NW TXK/ AND
   THROUGH NERN TX /30 N TYR/ TO CENTRAL AND SW TX.  THE PORTION OF THE
   BOUNDARY IN NERN TX TO NRN AR APPEARS TO HAVE BECOME MORE
   QUASI-STATIONARY DURING THE LAST 1-2 HOURS.  THE AIR MASS INVOF AND
   S OF THE COLD FRONT REMAINS QUITE MOIST...MODERATELY UNSTABLE AND
   STRONGLY SHEARED.  RECENT RADAR IMAGERY SHOWED A STORM OVER SWRN AR
   /MILLER COUNTY/ HAD TURNED LEFT MOVING MORE NNEWD WHICH SUGGESTS IT
   WAS NO LONGER ROOTED AT THE SURFACE.  HOWEVER...GIVEN THE AVAILABLE
   INSTABILITY AND STRONGLY SHEARED ENVIRONMENT INCLUDING IN THE LOW
   LEVELS...ANY STORM THAT CAN BECOME ROOTED AT THE SURFACE WILL HAVE A
   POTENTIAL TORNADO THREAT.  THIS APPEARS GREATEST ACROSS SRN INTO
   CENTRAL AR WHERE EFFECTIVE SRH IS 300-400 M2/S2.
   
   ..PETERS.. 05/01/2011
   
   
   ATTN...WFO...MEG...JAN...LZK...SHV...TSA...
   
   LAT...LON   34739443 35279304 35919174 36059089 35989030 34859036
               34209074 33869122 34079252 34089283 33739306 33249364
               32889389 32919442 33069495 33339524 34059519 34509500
               34739443