099 FXUS64 KHUN 252034 AFDHUN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HUNTSVILLE AL 334 PM CDT SAT MAY 25 2013 .DISCUSSION... THE TENNESSEE VALLEY REMAINS BENEATH A BROAD BELT OF NORTHWESTERLY FLOW ALOFT THIS AFTERNOON...WHICH IS BEING INDUCED BY A DEEP UPPER LOW ACROSS COASTAL NEW ENGLAND AND A HIGH AMPLITUDE MID-TROPOSPHERIC RIDGE EXTENDING FROM CENTRAL MEXICO NORTHWARD INTO SOUTHERN MANITOBA/ONTARIO. A WEAK 500-MB VORT MAX EXTENDING FROM SOUTHERN OKLAHOMA INTO NORTH/CENTRAL TEXAS IS EFFECTIVELY TRAPPED WITHIN THE RIDGE AXIS...AND IT IS THIS FEATURE THAT HAS BEEN RESPONSIBLE FOR THE SIGNIFICANT FLOODING EVENT ACROSS CENTRAL TEXAS FOR MUCH OF THE DAY TODAY. SHORT TERM MODELS ARE IN GOOD AGREEMENT THAT A SERIES OF MID-LEVEL WAVES EJECTING NORTHEASTWARD ACROSS THE CENTRAL/NORTHERN PLAINS AND INTO SOUTHERN CANADA -- AROUND ANOTHER UPPER LOW CENTERED OVER SOUTHERN BRITISH COLUMBIA/ALBERTA -- WILL WEAKEN THE CENTRAL PLAINS RIDGE FROM TONIGHT THROUGH SUNDAY. THIS WILL ALLOW THE SOUTHERN PLAINS DISTURBANCE TO FINALLY SHIFT EASTWARD...LIKELY REACHING THE LOWER MISSISSIPPI VALLEY ON SUNDAY EVENING. THE REMNANTS OF THIS WEAKENING MID-LEVEL WAVE WILL SPREAD EASTWARD ACROSS NORTHERN ALABAMA/SOUTHERN MIDDLE TENNESSEE ON MONDAY/MONDAY NIGHT...AND MAY PROVIDE JUST ENOUGH LARGE SCALE FORCING AND MID-LEVEL COOLING FOR THE DEVELOPMENT OF ISOLATED/WIDELY SCATTERED SHOWERS AND THUNDERSTORMS. WILL KEEP POPS ON THE LOW SIDE BASED ON PRESENCE OF MID-LEVEL DRY AIR /PWATS OF 1-1.20 INCHES/...THE WEAK NATURE OF FORCING...NO DISCERNIBLE SOURCE OF LOW-LEVEL CONVERGENCE...AND SUBSTANTIAL CINH EVIDENT IN POINT FORECAST SOUNDINGS FROM THE GFS/NAM/ECMWF/UKMET SUITE. HOWEVER...IF AN MCS TRACKS SOUTHEASTWARD ACROSS THE OHIO/UPPER TENNESSEE VALLEYS ON SUNDAY NIGHT...AS INDICATED BY SOME NWP GUIDANCE...AN OUTFLOW BOUNDARY FROM THIS FEATURE MAY PROVIDE WEAK LOW-LEVEL CONVERGENCE IN THE INCREASINGLY UNSTABLE ENVIRONMENT. GENERALLY WEAK WINDS THROUGH THE LOWER/MIDDLE TROPOSPHERE WOULD SUGGEST THAT THE MAIN THREATS -- IF STORMS INDEED DEVELOP -- WILL BE GUSTY WINDS AND FREQUENT LIGHTNING STRIKES. IN THE EXTENDED FORECAST PERIOD...GUIDANCE INDICATES THAT A BROAD MID-LEVEL HIGH WILL BECOME ESTABLISHED ACROSS THE SOUTHEASTERN CONUS BY TUESDAY -- DOWNSTREAM FROM AN AMPLIFIED LONGWAVE TROUGH PROGGED TO PUSH ONSHORE THE PACIFIC COAST LATE MONDAY OR MONDAY NIGHT. MEDIUM RANGE SOLUTIONS FROM THE GFS/ECMWF INDICATE THAT THIS MID/UPPER- LEVEL ANTICYCLONE WILL STRENGTHEN AND EXPAND NORTHEASTWARD INTO THE MID-ATLANTIC REGION THROUGH THE REMAINDER OF THE WORK WEEK...AS THE WESTERN CONUS LONGWAVE TROUGH SLOWLY SHIFTS EASTWARD AND BEGINS TO CLOSE OFF. ALTHOUGH THIS PATTERN WILL EFFECTIVELY END ANY THREAT FOR SHOWERS/THUNDERSTORMS UNTIL NEXT WEEKEND...A PERSISTENT SOUTHERLY WIND WILL ALLOW DEW POINTS TO CLIMB INTO THE LOWER/MID 60S...MAKING FOR VERY WARM/HUMID CONDITIONS WITH AFTERNOON HEAT INDICES IN THE LOWER 90S FOR MOST OF THE AREA. 70/DD && .AVIATION... /ISSUED 1231 PM CDT SAT MAY 25 2013/ FOR 18Z TAFS...RIDGING SURFACE AND ALOFT WILL CONTRIBUTE TO VFR CONDITIONS AND GENERALLY LIGHT AND VARIABLE WINDS THROUGH THE PERIOD. 15 && .PRELIMINARY POINT TEMPS/POPS... HUNTSVILLE 54 84 59 88 / 10 10 10 30 SHOALS 54 84 59 88 / 10 10 20 30 VINEMONT 50 81 55 84 / 10 10 10 30 FAYETTEVILLE 51 81 57 86 / 10 10 10 30 ALBERTVILLE 52 80 57 84 / 10 10 10 30 FORT PAYNE 46 80 53 85 / 10 10 10 30 && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WEATHER.GOV/HUNTSVILLE.