868 FXUS64 KHUN 081050 AAA AFDHUN AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE HUNTSVILLE AL 550 AM CDT THU AUG 8 2013 .UPDATE... FOR 12Z TAFS && .DISCUSSION... /ISSUED 306 AM CDT THU AUG 8 2013/ AN ANOMALOUS AND PERSISTENT VORTEX JUST SOUTHWEST OF THE HUDSON BAY WILL FINALLY MOVE OFF TO THE NORTHEAST OVER QUEBEC. THIS WILL LEAVE THE INFLUENCE OF TWO WEAKENED RIDGES (ONE OVER TX, ONE OVER THE ATLANTIC) OVER CENTRAL NORTH AMERICA. MID-LEVEL SHORTWAVE TROUGHS WITHIN A WEAKNESS BETWEEN THE RIDGE OVER THE SOUTHERN PLAINS AND THE TROUGH TO THE NORTHEAST WILL BECOME THE MAIN PLAYERS FOR WEATHER OVER THE SHORT TERM. THE UPPER FLOW PATTERN IS THEN EXPECTED TO BECOME AMPLIFIED IN THE LONG TERM. THE SOUTHEAST AND AREAS NORTH TO THE OHIO RIVER VALLEY ARE ENVELOPED WITHIN A MARITIME TROPICAL AIRMASS. THIS WILL TRANSLATE TO VERY EFFICIENT RAINFALL PRODUCING THUNDERSTORMS WHENEVER A LIFTING MECHANISM IS PRESENT. HOWEVER, DUE TO THIS ANOMALOUS SETUP FOR AUGUST (MULTIPLE ROUNDS OF SHOWERS/STORMS DURING THE FORECAST PERIOD), THE MODELS ARE HAVING GREAT DIFFICULTY RESOLVING THE TIMING OF EACH MID-LEVEL SHORTWAVE AND THE MOVEMENT OF A SFC FRONT LOCATED TO THE NORTHWEST OVER THE OH RIVER VALLEY. THUS, FOR TODAY, HAVE ACTUALLY REDUCED POPS DUE TO THE LACK OF CONVECTION FOR THIS MORNING AND WHAT LOOKS LIKE MAINLY SCT CONVECTION THIS AFTERNOON/EVENING. IN ADDITION, HAVE CHOSEN TO CANCEL THE FLASH FLOOD WATCH DUE TO THE LOW CONFIDENCE IN WIDESPREAD FLASH FLOODING. INSTANCES OF FLASH FLOODING MAY STILL OCCUR WITH ANY THUNDERSTORMS THAT DEVELOP DUE TO THE HIGH PWATS (TROPICAL AIR MASS). INSTABILITY PARAMETERS DO INDICATE MODERATE SB INSTABILITY (~1000 J/KG) LATER THIS AFTERNOON. THE MAIN IMPACTS WILL LIKELY BE GUSTY WINDS FROM OUTFLOW BOUNDARIES, HEAVY RAINFALL, AND FREQUENT LIGHTNING. ISOLATED THUNDERSTORMS MAY LINGER INTO THE EVENING TONIGHT. ANY BREAKS IN THE CLOUDS IN BETWEEN AND AFTER STORMS DISSIPATE MAY LEAD TO PATCHY FOG DEVELOPMENT. AS A RESULT, ADDED PATCHY FOG TO THE FORECAST. AS THE UPPER LOW MOVES OFF TO THE NORTHEAST OVER QUEBEC, SEVERAL MID- LEVEL SHORTWAVES WILL FLATTEN THE RIDGE BY FRIDAY WITH A SFC COLD FRONT PUSHING SOUTHWARD TOWARDS TN/NC/N AR. THIS WILL MEAN THE POSSIBILITY OF SHOWERS AND STORMS DEVELOPING OVER THE OH AND MID MS RIVER VALLEY/CENTRAL MO AND SLOWLY SPREADING SOUTHWARD. LEFT A GRADIENT POP IN THE FORECAST FROM NORTH TO SOUTH FOR FRIDAY. TEMPS ARE DEFINITELY CHALLENGING DURING THIS TIME PERIOD WITH BREAKS IN THE CLOUDS TRANSLATING TO DIFFERENTIAL HEATING OVER SOME AREAS. THUS, HAVE TRIED TO INCORPORATE SOME PERSISTENCE EXCEPT FOR SOMEWHAT HIGHER TEMPS ON FRIDAY WITH THE RIDGE (THOUGH WEAKER) MOVING EASTWARD FROM THE SOUTHERN PLAINS. BY SATURDAY, ADDITIONAL MID-LEVEL SHORTWAVES FLOWING BETWEEN THE WOBBLING RIDGE AND BROAD TROUGH TO THE NORTH MAY ACT TO PUSH THE SFC FRONT FROM TN TOWARDS AL SENDING A COUPLE OF WAVES OF STORMS OVER THE AREA. IF THIS FRONT ACTUALLY MOVES FAR ENOUGH SOUTH ON SATURDAY, THERE MAY NEED TO BE ADJUSTMENTS NEEDED TO THE WX FORECAST FOR SUNDAY AS POPS MAY BE ON THE WET SIDE. BY SUNDAY A RIDGE WILL BE BUILDING OVER THE WEST (AGAIN) LEADING TO AN AMPLIFICATION OF THE UPPER FLOW PATTERN AND WHAT APPEARS TO BE NW FLOW (AGAIN) FOR THE EASTERN PORTIONS OF CENTRAL NORTH AMERICA. THUS, HAVE LEFT A CHC OF THUNDERSTORMS IN THE FORECAST THROUGH THE REST OF THE EXTENDED. ONE THING TO KEEP IN MIND IS THAT THE FRONT MAY ACTUALLY PUSH COMPLETELY SOUTH OF THE HUNTSVILLE FORECAST AREA LATE IN THE PERIOD, WHICH COULD FINALLY DRY THE AREA, BUT UNTIL MORE CONSISTENCY IS SEEN WILL ONLY INCLUDE SOMEWHAT COOLER TEMPS ON TUESDAY/WEDNESDAY DURING THE OVERNIGHT. SL.77 && .AVIATION... FOR 12Z TAFS... VFR CONDS WILL LAST THRU MOST OF TODAY WITH THE EXCEPTION OF SOME AFTERNOON THUNDERSTORMS. THESE ARE MOST LIKELY TO DEVELOP ACROSS SOUTHERN TN INTO NORTHWEST AL, BUT HAVE INCLUDED THEM IN THE VICINITY AT BOTH KMSL AND KHSV THRU 01Z. PATCHY FOG IS LIKELY TO DEVELOP TONIGHT WITHIN THE VERY MOIST AIRMASS. AT THIS TIME, FORECAST MVFR VSBYS BEGINNING ~10Z, BUT A DOWNGRADE TO IFR/LIFR CANNOT BE RULED OUT IN LATER UPDATES DEPENDING ON RAINFALL THAT OCCURS TODAY AND IF THE SKY CAN CLEAR THIS EVENING. AK && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WEATHER.GOV/HUNTSVILLE.