032 FXUS64 KHUN 251058 AAA AFDHUN AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE HUNTSVILLE AL 558 AM CDT TUE JUN 25 2013 .UPDATE... FOR 12Z TAFS && .DISCUSSION... /ISSUED 521 AM CDT TUE JUN 25 2013/ GENERALLY QUIET CONDITIONS PREVAIL ACROSS THE CENTRAL TENNESSEE VALLEY THIS MORNING...WITH A SEASONABLY WARM/MOIST AIRMASS BEING MAINTAINED BY LIGHT SOUTHERLY LOW-LEVEL FLOW. WATER VAPOR SATELLITE DATA SUGGESTS THAT THE SUBTROPICAL MID-LEVEL HIGH IS NOW CENTERED ACROSS SOUTH CENTRAL TEXAS...WITH A WEAK 500-MB SHORTWAVE TROUGH EXTENDING FROM WEST VIRGINIA SOUTH-SOUTHWESTWARD INTO EAST CENTRAL ALABAMA. THIS WAVE IS FORECAST TO TRACK SLOWLY EASTWARD ACROSS THE SOUTHERN APPALACHIANS TODAY...AS THE MID-LEVEL RIDGE CONTINUES TO RETROGRADE ACROSS NORTHERN CHIHUAHUA/SOUTHWEST TEXAS. OVERALL...WE ARE EXPECTING CONDITIONS TODAY TO BE SIMILAR TO WHAT WAS OBSERVED YESTERDAY...WITH ISOLATED/WIDELY SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPING BY LATE MORNING/EARLY AFTERNOON. ALTHOUGH THE COVERAGE OF CONVECTION MAY BE A BIT LOWER TODAY AS WEAK MID-LEVEL SUBSIDENCE SHOULD BE PRESENT ACROSS THE REGION IN THE WAKE OF THE SHORTWAVE DEPARTING TO THE EAST...INCREASING DEEP-LAYER MOISTURE MAY OFFSET THIS TO SOME DEGREE. DESPITE A THICK DECK OF MORNING LOW STRATUS CLOUDS THAT WILL LIKELY ENCOMPASS MOST OF THE REGION...HIGH TEMPERATURES SHOULD HAVE NO TROUBLE WARMING INTO THE LOWER 90S ONCE AGAIN. BEGINNING TONIGHT...GLOBAL MODELS ARE IN GOOD AGREEMENT THAT THE PREVIOUSLY MENTIONED MID-LEVEL RIDGE WILL BEGIN TO EXPAND NORTHWARD INTO NEW MEXICO/ARIZONA -- RESULTING IN THE INITIAL DEVELOPMENT OF WEAK NORTHWEST FLOW ALOFT OVER THE LOCAL REGION. AS THIS OCCURS A MID- LEVEL SHORTWAVE TROUGH ADVANCING EASTWARD FROM SOUTHERN MISSOURI INTO THE LOWER OHIO VALLEY WILL BEGIN TO DIG SOUTHEASTWARD... POTENTIALLY BEGINNING TO IMPACT THE AREA EARLY WEDNESDAY MORNING. ALTHOUGH WE EXPECT LITTLE IN TERMS OF NOCTURNAL CONVECTION WITH THIS FEATURE...WEAK LIFT ASSOCIATED WITH ITS REMNANTS MAY RESULT IN A MINOR INCREASE IN THE COVERAGE OF SHOWERS AND STORMS AS IT PUSHES SOUTHEASTWARD DURING THE DAY ON WEDNESDAY. MODELS INDICATE THE PASSAGE OF YET ANOTHER/STRONGER WAVE IN THE NORTHWEST FLOW REGIME ON WEDNESDAY NIGHT...ALTHOUGH IT APPEARS NOW THAT THE STRONGEST FORCING FOR ASCENT WILL BE LOCATED NORTH/EAST OF THE FORECAST AREA. THUS... THE HIGHEST THREAT FOR IMPACTS FROM ANY MESOSCALE COMPLEX OF THUNDERSTORMS THAT MAY DEVELOP SHOULD BE NORTH OF THE AREA...AND WILL INDICATE A NORTH- SOUTH GRADIENT IN POPS TO REFLECT THIS. SOME LINGERING SHOWER AND THUNDERSTORM ACTIVITY WILL BE POSSIBLE -- ESPECIALLY ACROSS THE NORTHEASTERN PORTION OF THE AREA -- ON THURSDAY MORNING...PRIOR TO THE PASSAGE OF A SURFACE TROUGH AXIS WHICH WILL VEER LOW-LEVEL FLOW TO THE WEST. MAXIMUM TEMPERATURES WILL LIKELY REACH THE LOWER/MID 90S ON WEDNESDAY AS SOUTHWESTERLY FLOW STRENGTHENS IN THE MIXING LAYER. HOWEVER...BASED ON THE POTENTIAL FOR LINGERING CLOUDS AND MORNING PRECIPITATION...WILL TRIM A FEW DEGREES OFF MOS HIGH TEMPERATURES ON THURSDAY. MEDIUM RANGE GUIDANCE FROM ALL GLOBAL MODELS CONTINUES TO INDICATE THE PRESENCE OF A HIGHLY AMPLIFIED MID/UPPER-LEVEL FLOW REGIME ACROSS THE CONUS PERSISTING THROUGH THE EXTENDED PERIOD. THIS WILL OCCUR AS THE FOUR CORNERS MID-LEVEL RIDGE MIGRATES SLOWLY WESTWARD AND A STRONG UPPER LOW DIGS SOUTHWARD FROM THE GREAT LAKES -- EVENTUALLY DEVELOPING A LONGWAVE TROUGH OVER THE EASTERN CONUS. THE THREAT FOR SHOWERS/STORMS WILL CONTINUE THROUGH SATURDAY...AS SEVERAL DISTURBANCES MAY AFFECT THE REGION DURING THIS PERIOD. HOWEVER...A MORE SUBSTANTIAL COLD FRTON WILL ARRIVE LATE SATURDAY OR SATURDAY NIGHT...BRINGING BRINGING SLIGHTLY COOLER/DRIER AIR INTO THE REGION AND REDUCING PRECIPITATION CHANCES. WE CONTINUED TO TREND THE FORECAST TOWARD THE COOLER GFS ENSEMBLE MEAN...WITH HIGHS LATE IN THE FORECAST PERIOD EXPECTED TO ONLY REACH THE MID 80S. 70/DD && .AVIATION... FOR 12Z TAFS... IFR/MVFR CIGS HAVE DEVELOPED OVER A LARGE PORTION OF NORTH ALABAMA AND SOUTHERN TN. THUS FAR...THE CIGS HAVE AVOIDED THE KMSL VCNTY. THE CLOUDS SHOULD LIFT INTO A CU FIELD BY ~16Z. SCT TSRA ARE EXPECTED TO DEVELOP SOONAFTER. WILL FORECAST A LAYER OF CB AT BOTH KMSL AND KHSV THRU EARLY THIS EVENING. LOW CLOUDS SHOULD DEVELOP ONCE AGAIN LATE TONIGHT WITH A SIMILAR WX SITUATION IN PLACE. AK && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WEATHER.GOV/HUNTSVILLE.