629 FXUS62 KGSP 221418 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 1018 AM EDT WED MAY 22 2013 .SYNOPSIS... AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE REGION THROUGH THURSDAY. SOUTHERLY FLOW WILL KEEP THE AREA WARM AND GENERALLY UNSETTLED WITH STORM CHANCES EACH AFTERNOON. A COOLER AND DRIER AIRMASS SETTLES IN FOR THE WEEKEND AFTER A COLD FRONT MOVES THROUGH THURSDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF MID MORNING...A FEW SHOWERS AND THUNDERSTORMS ALREADY DEVELOPING ALONG A LINEAR FEATURE STRETCHING N TO S ACROSS NE GEORGIA. HAVE TWEAKED THE POP TO ACCOUNT FOR THIS EARLY DEVELOPMENT...AND LACK OF DEVELOPMENT ACROSS THE PIEDMONT. RAISED THE PRECIP CHANCES A BIT OVER THE WEST FOR LATE IN THE DAY WITH THE EXPECTATION THAT A LINE OR BAND OF STORMS WILL DEVELOP OVER THE TN VALLEY AND MAKE IT INTO THE FCST AREA. TEMPS LOOK OKAY. PREVIOUS DISCUSSION... AT 300 AM EST WEDNESDAY...AN UPPER TROUGH AXIS WILL SLOWLY CROSS THE MS RIVER VALLEY TODAY AND TONIGHT. A SHORTWAVE ROUNDING THIS UPPER TROUGH WILL REACH THE SOUTHERN APPALACHIANS THIS EVENING...CROSSING OUR AREA OVERNIGHT. A WEAKENING COLD FRONT WILL APPROACH OUR AREA FROM THE WEST TODAY...PRECEDED BY A BAND OF GULF MOISTURE...WHILE ATLANTIC MOISTURE MOVES NORTH INTO THE PIEDMONT. THESE MOISTURE BAND CONVERGE OVER OUR AREA TONIGHT. THE FRONT AND MOISTURE ALONG IT REACH THE INTERSTATE 77 CORRIDOR BY THURSDAY MORNING. ALTHOUGH INSTABILITY WILL PEAK DURING THE DAYLIGHT HOURS...WINDS SHEAR WILL INCREASE THIS EVENING...OPENING A WIDER WINDOW FOR SEVERE WEATHER POTENTIAL. THE MOISTENING AIR MASS WILL SUPPORT HEAVIER RAINFALL WITH TIME. STEERING FLOW WILL INITIALLY MOVE CELLS INTO THE BLUE RIDGE ESCARPMENT...BUT BY THE TIME THE BEST MOISTURE ARRIVES...CELL MOVEMENT SHOULD BE MORE PARALLEL TO THE HIGHER TERRAIN. THIS WILL LIMIT PRECIPITATION ACCUMULATION...AND NO LARGE SCALE HYDROLOGICAL PROBLEMS ARE FORESEEN AT THIS TIME. TEMPERATURES WILL RUN A CATEGORY OR TWO ABOVE NORMAL IN WARM ADVECTION. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 255 AM WEDNESDAY...SHORT WAVES MOVING THRU AN UPPER TROF PUSH THE TROF AXIS TOWARD THU THEN INTO THE AREA THU NITE. AT THE SFC... A PRE-FRONTAL TROF STARTS THE DAY OVER THE AREA WITH A COLD FRONT TO OUR WEST. THIS FRONT JUMPS INTO THE TROF BY THE END OF THE DAY AND MOVES EAST OF THE AREA THU NITE. THIS SETS UP TWO AREAS OF FORCING. ONE OVER THE ERN CWFA ALONG THE TROF AND OVER THE MTNS AHEAD OF THE FRONT. NE GA AND MUCH OF THE UPSTATE WILL BE BETWEEN THESE 2 AREAS. THEREFORE...HAVE PUT THE HIGHEST POP OVER THE AREAS WITH BEST FORCING...BUT DID KEEP LOW CHC POP OVER NE GA AND THE UPSTATE AS THERE WILL BE WEAK INSTABILITY IN PLACE. BEST INSTABILITY AND SHEAR WILL BE EAST OF THE AREA...SO DO NOT EXPECT ANY SIGNIFICANT COVERAGE OF SVR STORMS. PRECIP CHC DIMINISHES OUTSIDE OF THE MTNS DURING THE EVENING AS THE FRONT MOVES EAST. HOWEVER...SCT SHRA WILL LINGER OVER THE NC MTNS IN THE DEVELOPING NW FLOW AND CONTINUED LOW LEVEL MOISTURE. HIGHS THU AROUND 5 DEGREES ABOVE NORMAL WITH LOWS A COUPLE OF DEGREES ABOVE NORMAL THU NITE. THE UPPER TROF AXIS MOVES EAST OF THE AREA FRI WITH NWLY FLOW REMAINING IN PLACE FRI NITE...WHILE SFC HIGH PRESSURE SLOWLY BUILDS TOWARD THE AREA. ANY LINGERING NW FLOW SHRA END BY AFTERNOON. THE BIGGER STORIES WILL BE THE WINDS AND COLD AIR MASS MOVING IN. EXPECT WINDY CONDITIONS TO DEVELOP AS MIXING TAPS SIGNIFICANT LOW LEVEL WINDS. THAT SAID...IT LOOKS LIKE WINDS AND GUSTS WILL REMAIN BELOW WIND ADV LEVELS. HIGHS FRI WILL BE 5 TO 10 DEGREES BELOW NORMAL WHILE LOWS FRI NITE END UP 10 TO 15 DEGREES BELOW NORMAL. RIGHT NOW IT LOOKS LIKE WINDS WILL REMAIN TOO STRONG FOR ANY SIGNIFICANT FROST FORMATION OVER THE NC MTNS. HOWEVER...WILL HAVE TO KEEP AN EYE ON THIS AS TEMPS APPROACH FROSTY LEVELS. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 355 AM WEDNESDAY...THE GFS AND ECMWF ARE IN GENERAL AGREEMENT THRU THE MEDIUM RANGE. HOWEVER...THERE ARE SOME DETAIL DIFFERENCES. NWLY UPPER FLOW REMAINS OVER THE AREA SAT AND SUN AS THE CWFA WILL BE BETWEEN A TROF TO OUR EAST AND A RIDGE TO OUR WEST. THE FLOW BECOMES ZONAL FOR MONDAY WITH WEAK RIDGING TUE. ALL THIS TIME... SERIES OF SHORT WAVES MOVE THRU THE FLOW AND ACROSS THE AREA. AT THE SFC...HIGH PRESSURE RIDGES IN FROM THE NW...BUT IS SPLIT BY A WEAK BACK DOOR COLD FRONT. THIS FRONT REMAINS OVER OR NEAR THE AREA MON AND TUE. PRECIP ACTIVATES ALONG THE FRONT FROM TIME TO TIME AS THE WAVES MOVE OVER. HOWEVER...THE ECMWF IS MUCH MORE WIDESPREAD WITH PRECIP THAN THE GFS. FOR NOW...HAVE FOLLOWED NATIONAL GUIDANCE AND KEEP PRECIP LIMITED TO SLIGHT CHC XCPT ACROSS THE NRN MTNS FROM MON NITE ON. HIGHS AROUND 5 DEGREES BELOW NORMAL SAT AND SUN...NEAR NORMAL MON...THEN ABOUT 5 DEGREES ABOVE NORMAL TUE. LOWS 5 TO 10 DEGREES BELOW NORMAL SAT NITE...NEAR NORMAL SUN NITE...THEN A LITTLE ABOVE NORMAL MON NITE. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... AT KCLT...IFR CIGS HAS BROKEN UP...BUT A TEMPO FOR IFR CIG WILL BE CARRIED IN THE TAF EARLY THIS MORNING. MVFR VSBY HAS BEEN FAIRLY STABLE FOR SEVERAL HOURS...AND WILL BE MAINTAINED FOR ANOTHER HOUR. BY MID MORNING LOW VFR CLOUDS AND UNRESTRICTED VSBY ARE EXPECTED. MODEL SOUNDINGS SUPPORT AFTERNOON AND EARLY EVENING CONVECTION WITH MOISTURE MOVING IN FROM THE SOUTH. SOUTHERLY WINDS WILL APPROACH 10 KNOTS THIS AFTERNOON...WITH GUSTS. A BLEND OF MODEL GUIDANCE DOES NOT SUPPORT RESTRICTIONS EARLY THURSDAY. ELSEWHERE...RESTRICTIONS WILL BE CARRIED FOR THE FIRST HOUR AT KGSP AND KHKY PER OBSERVATION...AND AT KAVL WHERE TOW VERY LOW CLOUDS LAYERS ARE PRESENT. KGMU AND KAND APPEAR TO HAVE LESS OF A CHANCE OF RESTRICTIONS. LOW VFR CLOUDS WILL PREVAIL MOST OF TODAY...WITH CONVECTION DEVELOPING BY THIS AFTERNOON AS A WEAKENING COLD FRONT APPROACHES. ALTHOUGH CONVECTION WILL TAPER OFF TONIGHT...IT MAY CONTINUE AT A DIMINISHED RATE AS THE FRONT GETS CLOSER...ESPECIALLY IN THE MOUNTAINS. THE TAFS WILL FOCUS ON THE MOST LIKELY TIMING OF CONVECTION. SSW WINDS WILL APPROACH 10 KNOTS TODAY...WITH GUSTS. A BLEND OF MODEL GUIDANCE SUPPORTS MVFR FOG AT KAVL EARLY THURSDAY MORNING...WITH LOW VFR AT ALL OTHER SITES BUT KAND. OUTLOOK... CEILING AND VISIBILITY RESTRICTIONS IN SCATTERED SHOWERS AND THUNDERSTORMS AGAIN THURSDAY AFTN/EVE. GENERALLY VFR WEATHER FRIDAY AND SATURDAY. CONFIDENCE TABLE... 14-20Z 20-02Z 02-08Z 08-14Z KCLT HIGH 97% HIGH 100% HIGH 95% HIGH 96% KGSP HIGH 97% HIGH 100% HIGH 90% MED 69% KAVL HIGH 98% HIGH 98% HIGH 82% MED 64% KHKY HIGH 94% HIGH 100% HIGH 86% LOW 56% KGMU HIGH 96% HIGH 100% HIGH 93% MED 69% KAND HIGH 96% HIGH 100% HIGH 93% MED 78% THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE) WWW.WEATHER.GOV/GSP/AVIATION_TABLES && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...RWH NEAR TERM...JAT/PM SHORT TERM...RWH LONG TERM...RWH AVIATION...JAT