MESOSCALE DISCUSSION 0642 NWS STORM PREDICTION CENTER NORMAN OK 0755 PM CDT WED APR 27 2011 AREAS AFFECTED...MUCH OF AL AND NORTHWEST/WEST-CENTRAL GA CONCERNING...TORNADO WATCH 235... VALID 280055Z - 280200Z THE SEVERE WEATHER THREAT FOR TORNADO WATCH 235 CONTINUES. PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH 235 CONTINUES UNTIL 03Z...WITH A CONTINUED HIGH-END RISK FOR STRONG/PERHAPS VIOLENT TORNADOES ESPECIALLY ACROSS A LARGE PART OF EAST-CENTRAL/SOUTH-CENTRAL AL INTO NORTHWEST GA. GIVEN A SCHEDULED 03Z EXPIRATION OF TORNADO WATCH 235...EARLY INDICATIONS ARE THAT A REPLACEMENT TORNADO WATCH WILL LIKELY BE NEEDED. THIS REMAINS A POTENTIALLY LIFE-THREATENING SCENARIO. NOT SURPRISING GIVEN A NUMBER OF DESTRUCTIVE TORNADOES SINCE THIS AFTERNOON...THE 00Z OBSERVED BIRMINGHAM RAOB SAMPLED A CLASSIC STRONG TORNADO ENVIRONMENT/PARAMETER SPACE...HIGHLIGHTED BY HIGH BOUNDARY LAYER MOISTURE CONTENT AND VERY STRONG 0-1 KM SRH OF 450 M2/S2 VIA A LONG CURVING HODOGRAPH WITHIN THE LOWEST 1-2 KM. WITH TIME...OBSERVATIONAL TRENDS/SHORT TERM GUIDANCE SUGGEST THE STRONGEST 1-2 KM FLOW WILL CONTINUE TO SHIFT EAST-NORTHEASTWARD ACROSS EASTERN AL INTO NORTHERN GA/THE SOUTHERN APPALACHIANS VICINITY. THERMODYNAMICALLY...THE BOUNDARY LAYER WILL BE VERY SLOW TO DECOUPLE AFTER DARK GIVEN THE HIGH MOISTURE CONTENT...AMID LOWER 70S F SURFACE DEWPOINTS AND 16 G/KM MEAN MIXING RATIO PER THE 00Z BIRMINGHAM RAOB. OF NOTE...ONGOING TORNADIC SUPERCELLS ASIDE...SHORT TERM OBSERVATIONAL TRENDS IMPLY THAT ADDITIONAL STORMS/SUPERCELLS ARE LIKELY TO CONTINUE TO DEVELOP/INCREASE IN THE SHORT-TERM ACROSS SOUTH-CENTRAL/EAST-CENTRAL AL AMID A ZONE OF SHARPENING LOW LEVEL CONFLUENCE. THIS WOULD INCLUDE THE VICINITY OF MONTGOMERY AND NEARBY I-65/I-85 GENERAL VICINITIES. ACCORDINGLY...SUSTAINED/RELATIVELY DISCRETE TORNADIC SUPERCELLS...WITH CONTINUED STRONG/PERHAPS VIOLENT TORNADO POTENTIAL...ARE LIKELY TO PERSIST WITHIN A WSW-ENE ORIENTED BROAD CORRIDOR ACROSS A LARGE PART OF CENTRAL/PORTIONS OF SOUTHERN AL INTO NORTHWEST/WEST-CENTRAL GA THIS EVENING. ..GUYER.. 04/28/2011