MESOSCALE DISCUSSION 0634 NWS STORM PREDICTION CENTER NORMAN OK 0501 PM CDT WED APR 27 2011 AREAS AFFECTED...MUCH OF MS/AL TO NORTHWEST GA CONCERNING...TORNADO WATCH 232...235... VALID 272201Z - 272330Z THE SEVERE WEATHER THREAT FOR TORNADO WATCH 232...235...CONTINUES. PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCHES 232/235 CONTINUE UNTIL 00Z/03Z RESPECTIVELY. A TORNADO OUTBREAK WILL CONTINUE INTO THIS EVENING ACROSS MUCH OF MS/AL INTO NORTHWEST GA. THIS IS AN EXTREMELY DANGEROUS/LIFE-THREATENING SITUATION! CITIES AND AREAS AT GREATEST RISK INCLUDE BIRMINGHAM...HUNTSVILLE...THE I-59 CORRIDOR OF NORTHERN AL...AND I-65 NEAR/NORTH OF BIRMINGHAM. A NUMBER OF SEMI-DISCRETE/LONG-LIVED TORNADIC SUPERCELLS CONTINUE TO FORM WITHIN A PRE-DRYLINE/PRE-COLD FRONTAL WARM SECTOR FROM SOUTH-CENTRAL MS NORTHEASTWARD INTO MUCH OF NORTHERN AL. OTHER TORNADIC STORMS CONTINUE TO INTERACT WITH A MODIFYING EFFECTIVE WARM FRONTAL-TYPE BOUNDARY ACROSS FAR NORTHERN AL IN THE GENERAL VICINITIES OF DECATUR/HUNTSVILLE. THE SPATIALLY WIDE WARM SECTOR IS VERY UNSTABLE AMID MIDDLE-UPPER 60S F SURFACE DEWPOINTS...WITH LOWER 70S F SURFACE DEWPOINTS ACROSS PORTIONS OF SOUTHERN/MS. MLCAPE VALUES ARE AS HIGH AS 2000-4000 J/KG WITHIN THE WEAKLY CAPPED WARM SECTOR. RECENT REGIONAL WSR-88D VWP DATA IS INDICATIVE OF AN INCREASE IN LOW LEVEL WIND SPEEDS/HODOGRAPH CURVATURE OVER THE PAST FEW HOURS...WITH 0-1 KM SRH VALUES NOW ESTIMATED TO BE IN EXCESS OF 300-400 M2/S2 AND 0-3 KM SRH IN EXCESS OF 600 M2/S2 PER BIRMINGHAM/HUNTSVILLE WSR-88D VWPS. THIS WILL REMAIN HIGHLY FAVORABLE FOR LONG-LIVED STRONG/POTENTIALLY VIOLENT TORNADOES WITH ANY SUSTAINED SUPERCELLS WITHIN THE BROAD/VOLATILE WARM SECTOR INTO THIS EVENING. WHILE STRONG TORNADOES WILL BE POSSIBLE WITH ANY SUSTAINED SUPERCELLS WITHIN PDS TORNADO WATCH 232/235...THE RELATIVELY HIGHEST CONCERN OVER THE NEXT FEW HOURS WOULD APPEAR TO BE ACROSS WEST-CENTRAL AL AND NORTHERN HALF OF AL INTO FAR NORTHWEST GA. HERE...IN ADDITION TO THE AFOREMENTIONED RESIDUAL SURFACE BOUNDARY...RELATIVELY STRONG/BACKED LOW LEVEL FLOW IS EVIDENT IN 21Z SUBJECTIVE ANALYSIS AMID A RELATIVE MAXIMA OF 2-HR PRESSURE FALLS...ESPECIALLY ALONG/NORTH OF I-20 IN NORTHERN AL. ..GUYER.. 04/27/2011