855 FXUS64 KHUN 062338 AFDHUN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HUNTSVILLE AL 638 PM CDT TUE AUG 6 2013 .UPDATE... FOR 00Z TAFS && .DISCUSSION... /ISSUED 428 PM CDT TUE AUG 6 2013/ A SEASONABLY STRONG WEST-NORTHWEST FLOW REGIME ALOFT CONTINUES ACROSS NORTHERN ALABAMA/SOUTHERN MIDDLE TENNESSEE...BETWEEN A MID- TROPOSPHERIC HIGH LOCATED ACROSS CENTRAL/EAST TEXAS AND A BROAD TROUGH OVER NEW ENGLAND. THE FIRST IN A SERIES OF WEAKER IMPULSES EMBEDDED IN THIS FLOW HAS NOW PUSHED SOUTHEAST OF THE LOCAL AREA... BUT NOT BEFORE BRINGING AN INITIAL ROUND OF THUNDERSTORMS AND TORRENTIAL RAINFALL TO THE REGION THIS MORNING. SHORT TERM MODELS INDICATE THAT ANOTHER MID- LEVEL WAVE -- CURRENTLY LOCATED ACROSS SOUTHEASTERN MISSOURI -- WILL TRACK SOUTHEASTWARD FOR THE REMAINDER OF THE AFTERNOON/EVENING...BRINGING AT LEAST ONE ADDITIONAL CLUSTER OF SHOWERS/THUNDERSTORMS TO THE REGION. HOWEVER...FLOW ALOFT IS FORECAST TO DIMINISH AND BACK TO THE WEST OVERNIGHT AS THE NEW ENGLAND TROUGH LIFTS NORTHEASTWARD...AND THIS SUGGESTS THAT THE STRONGEST DEEP-LAYER FORCING FOR ASCENT WILL PRIMARILY BE ACROSS NORTHEAST ALABAMA/SOUTHERN MIDDLE TENNESSEE AS THE VORT MAX BEGINS TO ASSUME A MORE EAST-SOUTHEASTERLY HEADING. DURING THE PERIOD FROM WEDNESDAY THROUGH WEDNESDAY NIGHT...SOLUTIONS FROM ALL OF THE GLOBAL MODELS INDICATE THAT THE SOUTHERN PLAINS MID-LEVEL RIDGE WILL ATTEMPT TO BUILD EAST-NORTHEASTWARD IN RESPONSE TO A 500-MB TROUGH SHIFTING NORTHEASTWARD FROM THE FOUR CORNERS TO THE CENTRAL ROCKIES. ALTHOUGH THIS PATTERN WOULD NORMALLY RESULT IN A REDUCTION IN PRECIPITATION CHANCES...IT APPEARS THAT THE LOCAL AREA WILL REMAIN ON THE SOUTHERN FRINGE OF STRONGER NORTHWEST FLOW ALOFT...AND THERE ARE SOME INDICATION OF ANOTHER VORT MAX DIGGING SOUTHEASTWARD TOWARD THE SOUTHERN APPALACHIANS DURING THIS PERIOD. THIS WILL WARRANT LEAVING BOTH HIGH POPS INTACT AND THE FLASH FLOOD WATCH IN EFFECT THROUGH THURSDAY MORNING...AND WILL ALSO MENTION HEAVY RAINFALL IN THE ZFPHUN. FROM THURSDAY THROUGH THURSDAY NIGHT... THE CENTRAL ROCKIES MID-LEVEL SHORTWAVE TROUGH IS FORECAST TO SHIFT SLOWLY EASTWARD INTO THE CENTRAL PLAINS...WITH A BROAD SUBTROPICAL RIDGE BECOMING ESTABLISHED ALONG 35N LATITUDE. AS THIS RIDGE BECOMES POSITIONED DIRECTLY OVER THE FORECAST AREA...TEMPERATURES WILL INCREASE AS CLOUDS/RAIN CHANCES DIMINISH. MID-LEVEL HEIGHT RISES AND RIDGING WILL CONTINUE TO BE THE PRIMARY FEATURE OF INTEREST ON FRIDAY/FRIDAY NIGHT...WITH MAINLY DIURNAL CONVECTION POSSIBLE AS TEMPERATURES WARM INTO THE LOWER 90S. HOWEVER...CONDITIONS WILL BECOME MORE FAVORABLE FOR SHOWERS/STORMS ONCE AGAIN BY SATURDAY AS A STRONG EASTERLY WAVE LIFTING NORTHWESTWARD THROUGH THE CENTRAL GULF OF MEXICO INDUCES A BROAD WEAKNESS IN THE SUBTROPICAL RIDGE ACROSS THE SOUTHEASTERN STATES. A WEAK WEST-NORTHWEST FLOW MAY ALSO REDEVELOP OVER THE AREA BY THE SECOND HALF OF THE WEEKEND...AS A MID/UPPER-LEVEL CYCLONE DEEPENS ACROSS ONTARIO/QUEBEC...AND THE AXIS OF THE SUBTROPICAL RIDGE SHIFTS TO THE SOUTH/WEST OF THE REGION. ALTHOUGH THERE ARE DISCREPANCIES AMONG THE GFS/GEM/ECMWF...A WEAK COLD FRONT MAY ALSO ACCOMPANY THE TRANSITION TO A STRONGER NORTHWEST FLOW ALOFT...POTENTIALLY BRINGING A SLIGHTLY DRIER AIRMASS INTO THE REGION EARLY NEXT WEEK. 70/DD && .AVIATION... FOR 00Z TAFS...AN UPPER DISTURBANCE CONTINUES MOVE ACROSS THE CWA WITH MAINLY SCT SHRA THIS EVENING. AS THIS DISTURBANCE MOVES SE OF THE TN VALLEY THE PCPN WILL TAPER OFF BEGINNING ARND 02Z AT KMSL AND 03Z AT KHSV. ANOTHER DEVELOPING DISTURBANCE NOW OVER WRN KS WILL GET CAUGHT UP IN NW FLOW AND SHOULD BEGIN TO AFFECT THE TAF SITES BETWEEN 10Z AND 11Z EARLY WEDNESDAY MRNG. WILL CONTINUE TO KEEP THE CHC OF TSRA IN TAFS THRU THE END OF THE FCST PERIOD. OTHERWISE EXCEPT FOR MVFR CONDITIONS IN TSRA...VFR CONDITIONS ARE EXPECTED FOR THE NEXT 24 HOURS. 07 && .HUN WATCHES/WARNINGS/ADVISORIES... AL...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR ALZ001>010-016. TN...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR TNZ076-096-097. && $$ FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WEATHER.GOV/HUNTSVILLE.