MESOSCALE DISCUSSION 0642 MESOSCALE DISCUSSION 0629 NWS STORM PREDICTION CENTER NORMAN OK 0256 PM CDT WED APR 27 2011 AREAS AFFECTED...MUCH OF MS/AL INTO SOUTHERN TN AND NORTHWEST GA CONCERNING...TORNADO WATCH 232...235... VALID 271956Z - 272200Z THE SEVERE WEATHER THREAT FOR TORNADO WATCH 232...235...CONTINUES. PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCHES 232/235 CONTINUE UNTIL 00Z/03Z RESPECTIVELY. THIS INCLUDES THE POTENTIAL FOR LONG-TRACK STRONG/PERHAPS VIOLENT TORNADOES INTO THIS EVENING AS A SEVERE WEATHER OUTBREAK ONLY INCREASES IN MAGNITUDE/RISK. AN EXTREMELY DANGEROUS/LIFE-THREATENING SITUATION CONTINUES TO UNFOLD THIS AFTERNOON ACROSS A LARGE PART OF MS/AL...WITH ADJACENT PORTIONS OF TN/NORTHWEST GA ALSO EXPECTED TO BECOME A CONCERN LATE THIS AFTERNOON/EVENING. CURRENT OBSERVATIONAL TRENDS...REASONABLY SUPPORTED BY EXPERIMENTAL HRRR GUIDANCE...IMPLY THAT SCATTERED SUPERCELLS WILL CONTINUE TO FORM IN BROKEN NNE-SSW ORIENTED CORRIDORS OF SUBTLE CONFLUENCE AHEAD /EAST/ OF MORE STORMS/SUPERCELLS THAT ARE DEVELOPING ALONG A PRE-COLD FRONTAL TROUGH/DRYLINE GENERALLY NEARING I-55 IN MS. THE WARM SECTOR AIRMASS HAS AGGRESSIVELY DESTABILIZED THIS AFTERNOON AMID NEAR 70F/LOWER 70S F SURFACE DEWPOINTS...REFERENCE SPECIAL 18Z OBSERVED RAOBS FROM JACKSON MS/BIRMINGHAM AL...WITH A WIDE/HIGHLY SHEARED MOIST SECTOR IN PLACE ALONG/SOUTH OF A MODIFYING WEST-EAST OUTFLOW BOUNDARY /NOW AN EFFECTIVE WARM FRONT/ ACROSS FAR NORTHERN PORTIONS OF AL/MS. EXTREME LOW LEVEL SHEAR...VIA LONG/CURVING LOW LEVEL HODOGRAPHS...WILL REMAIN HIGHLY CONDUCIVE FOR SUPERCELLS CAPABLE OF LONG-TRACK STRONG/VIOLENT TORNADOES INTO THIS EVENING AMID 0-1 KM SRH OF 300-500 M2/S2 OR GREATER /ESPECIALLY NEAR THE AFOREMENTIONED NORTHERN MS AND AL BOUNDARY/. ..GUYER.. 04/27/2011