139 FXUS64 KBMX 222348 AFDBMX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BIRMINGHAM AL 648 PM CDT WED MAY 22 2013 .UPDATE... FOR 00Z AVIATION. && .DISCUSSION... TODAY'S FORECAST IS BROUGHT TO YOU BY THE LETTERS MCS... AS IN MESOSCALE CONVECTIVE SYSTEMS CAN REALLY MESS WITH A FORECAST. SHOWERS AND THUNDERSTORMS HAVE BEEN VERY SLOW TO DEVELOP THIS AFTERNOON ACROSS CENTRAL ALABAMA SINCE WIDESPREAD MID AND HIGH CLOUDS LEFTOVER FROM THE NOW DEFUNCT OVERNIGHT MCS IN MISSISSIPPI HAVE SLOWED THE RATE OF HEATING TODAY. AS OF 3 PM CDT... MANY LOCATIONS ARE JUST NOW REACHING THEIR CONVECTIVE TEMPERATURES... AND A FEW SHOWERS AND THUNDERSTORMS HAVE FORMED ALONG A SURFACE TROUGH AND DIFFERENTIAL HEATING ZONE IN OUR NORTHEASTERN AREA AROUND ANNISTON AND GADSDEN. BACK IN MISSISSIPPI PRECIP IS STRUGGLING TO GET GOING ALONG/JUST AHEAD OF THE COLD FRONT DUE TO THOSE LEFTOVER CLOUDS MENTIONED ABOVE. WITH DECENT LOW LEVEL MOISTURE IN PLACE AND SBCAPE OF 1500 TO 2000 J/KG ACROSS THE EASTERN HALF OF THE AREA... STILL THINK SOME SCATTERED DEVELOPMENT WILL OCCUR FOR A MAJORITY OF CENTRAL ALABAMA THIS AFTERNOON AND EARLY EVENING AS A SHORTWAVE TROUGH MOVING OVER WESTERN TENNESSEE GLANCES THE REGION TO THE NORTH. LOOKING AT SEVERE POTENTIAL FOR THE REST OF THE AFTERNOON... THE WIND SHEAR NEEDED TO ORGANIZE STORMS IS TOO WEAK... 30 KT OR LESS. SO WHILE SOME STRONG STORMS WITH SMALL HAIL AND GUSTY WINDS WILL BE POSSIBLE GIVEN THE INSTABILITY AND SURFACE COLD FRONT APPROACHING FROM MISSISSIPPI... THINK THAT STORMS FOR CENTRAL ALABAMA SHOULD REMAIN BELOW SEVERE LEVELS. HAVE KEPT IN A CHANCE FOR SHOWERS AND A SLIGHT CHANCE FOR A THUNDERSTORM TONIGHT FOR LOCATIONS ALONG AND SOUTHEAST OF THE I-20/59 CORRIDOR. PRECIP CHANCES DECREASE BY THURSDAY MORNING... AND HAVE ONLY KEPT IN SLIGHT CHANCE POPS FOR THE SOUTHEAST BEFORE 10 AM. OTHERWISE EXPECT THURSDAY TO BE RAIN FREE ACROSS CENTRAL ALABAMA. FRIDAY A SECONDARY SURGE OF COOLER AIR WILL MOVE INTO THE AREA AS THE UPPER TROUGH ADVANCES TO THE EASTERN SEABOARD. THIS WILL BRING OUR HIGHS DOWN BELOW AVERAGE FOR THE NORTHERN PORTIONS OF CENTRAL ALABAMA. ALSO... MORNING LOWS ON SATURDAY LOOK TO BE QUITE COOL FOR THIS TIME OF YEAR... UPPER 40S NORTH TO LOW/MID 50S SOUTH. BEHIND THE DEPARTURE OF THE UPPER TROUGH... SURFACE HIGH PRESSURE WILL SETTLE OVER THE SOUTHEAST FOR THE WEEKEND. BASED OFF THIS HIGH PRESSURE MOVING IN AND THE SOMEWHAT DRIER AIR BEHIND THE SECONDARY SURGE OF COOLER AIR FRIDAY... NOT EXPECTING PRECIP FOR SATURDAY OR SUNDAY. HOWEVER... WITH THE DEPARTURE OF THE UPPER TROUGH TO OUR EAST... CENTRAL ALABAMA WILL BE PLACED IN NORTHWEST FLOW ALOFT FROM SATURDAY THROUGH ABOUT NEXT TUESDAY. UNDER THIS SETUP AND GIVEN SUFFICIENT MOISTURE... WE OFTEN GET MCS FEATURES MOVING FROM ARKANSAS/NORTHERN MISSISSIPPI INTO THE AREA IN THE AFTERNOON/EVENING TIME FRAME. THE 12Z ECMWF IS HINTING AT THIS POSSIBILITY EACH AFTERNOON FROM SATURDAY THROUGH TUESDAY. IT DOES KEEP THE BULK OF THE PRECIP EITHER TO THE NORTH OR WEST OF CENTRAL ALABAMA... BUT IT IS SOMETHING TO KEEP IN MIND. OF COURSE... THE GFS KEEPS THINGS DRY FOR THE ENTIRE EXTENDED PERIOD WITH A STRONGER UPPER LEVEL RIDGE IN PLACE AND THE DISTURBANCES ROUNDING THE CREST OF THE RIDGE TO THE NORTH OF ALABAMA. IN KEEPING WITH THE PREVIOUS FORECAST PACKAGE... HAVE KEPT POPS OUT OF THE FORECAST FROM FRIDAY THROUGH NEXT WEDNESDAY. IF BOTH THE GFS AND ECMWF BEGIN TO AGREE ON A SPECIFIC DAY (OR DAYS) FOR POSSIBLE MCS DEVELOPMENT... THEN POPS MAY HAVE TO BE ADDED. BUT MCS FORMATION IN NORTHWEST FLOW IS USUALLY VERY DIFFICULT FOR THE GLOBAL SCALE MODELS TO PICK UP ON... ESPECIALLY THIS FAR OUT. SO ITS BASICALLY WAIT AND SEE. REGARDLESS.... WEEKEND TEMPS LOOK VERY NICE IN THE MID TO UPPER 80S. 77/GLEASON && .AVIATION... 00Z TAF DISCUSSION. SHOWERS AND THUNDERSTORMS ARE DECREASING IN COVERAGE AND INTENSITY WITH THE LOSS OF DAYTIME HEATING. A RUMBLE OF THUNDER OR TWO COULD CONTINUE AT KANB OVER THE NEXT HOUR OR SO. SHOWERS ARE TOO SCATTERED TO ADD ANY MENTION OF PRECIPITATION IN THE TAFS. WATER VAPOR IMAGERY INDICATES RATHER DRY AIR PUNCHING INTO WESTERN ALABAMA BEHIND THE FRONT. MODEL SOUNDINGS INDICATE LINGERING LOW LEVEL MOISTURE BEHIND THE FRONT AND HAVE INTRODUCED IFR CONDITIONS LATE TONIGHT ACROSS THE TERMINALS. BOUNDARY LAYER WINDS APPEAR TO BE TOO STRONG FOR WIDESPREAD FOG ISSUES. THE LOW LEVELS SHOULD MIX OUT FAIRLY QUICKLY TOMORROW MORNING GIVING WAY TO VFR CONDITIONS. 05/MA && .BMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$