544 FXUS62 KGSP 031113 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 713 AM EDT THU OCT 3 2013 .SYNOPSIS... WEAK UPPER LEVEL DISTURBANCES WILL PASS BY ALONG THE MOUNTAINS TODAY....BUT WITH HIGH PRESSURE OTHERWISE REMAINING ACROSS THE REGION THROUGH SATURDAY. A COLD FRONT...POSSIBLY ENHANCED WITH TROPICAL MOISTURE...WILL APPROACH FROM THE WEST ON SUNDAY EVENING AND BRING UNSETTLED AND RAINY WEATHER TO THE AREA FOR SUNDAY NIGHT THROUGH MONDAY. HIGH PRESSURE WILL RETURN BEHIND THE PASSING DISTURBANCE ON TUESDAY AND STRENGTHEN THROUGH MIDWEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 700 AM EDT...KGSP RADAR CONTINUES TO SHOW SPORADIC 20 TO 25 DBZ ECHOES ALONG MAINLY THE SPINE OF THE SOUTHERN APPALACHIANS AT DAYBREAK. ADDITIONAL WEAK FORCING FROM UPPER WAVES PASSING ALONG THE NC/TN BORDER MAY DRIVE VERY LIGHT ISOLD RAIN SHOWERS...BUT ANY PRECIP SHOULD BE CONFINED TO MAINLY THE HIGHER ELEVATIONS AND THE FAR WRN MTNS. THE CURRENTLY PASSING SHORTWAVE WILL LIFT NWD THROUGH THE CENTRAL APPALACHIANS TODAY...FOLLOWED BY A TRAILING SHORTWAVE INTO THE AFTN HOURS. MAINLY MID AND HIGH LEVEL CLOUDS WILL CONTINUE E OF THESE WAVES FOR A GOOD PART OF THE DAY. THE NAM CONTINUES TO SHOW MORE ROBUST QPF OVER THE MTNS TODAY...ATTRIBUTED MAINLY TO LESS CAPPING IN THE PROFILES. THIS APPEARS TO BE OVERDONE IN COMPARISON TO THE OTHER NUMERICAL MODELS...SO WILL LEAN STRONGLY TOWARD THE DRIER GFS AND RAP SOLUTIONS...WITH ONLY ISOLATED SHOWERS ALONG THE MTN CHAIN AND DRY CONDITIONS EAST. DESPITE THE ABUNDANT MID/HIGH CLOUDS...LOW LEVEL THICKNESSES WILL REACH OR SURPASS YESTERDAY VALUES...WITH COMPARABLE MAXES OR TEMPS POSSIBLY A DEGREE WARMER IN ERN SECTIONS. FLAT RIDGING WILL THEN REDEVELOP BEHIND THE DEPARTING WAVES TONIGHT. THE OPERATIONAL MOS IS QUITE COOL FOR MIN TEMPS...BUT WILL LEAN HEAVILY TOWARD THE WARMER BIAS CORRECTED VALUES AS THE AIRMASS CONTINUES TO MODIFY. ANOTHER ROUND OF EARLY MORNING MOUNTAIN VALLEY CAN BE EXPECTED OVERNIGHT. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 120 AM EDT THURSDAY...NO SIGNIFICANT CHANGES FROM THE PREVIOUS FORECAST FOR THE SHORT TERM PERIOD. WEAK DEEP LAYER RIDGING WILL PREVAIL THROUGH SATURDAY KEEPING CONDITIONS MOSTLY SUNNY AND DRY. MODEL GUIDANCE STILL CONTINUES TO INDICATE A FEW SHOWERS ALONG THE RIDGETOPS WHERE CAPPING WILL BE WEAKEST. THUS KEPT MENTION OF SLIGHT CHANCE POPS IN THE FORECAST FOR BOTH FRIDAY AND SATURDAY ACROSS THE HIGH TERRAIN. MEANWHILE...POTENTIAL TROPICAL DISTURBANCE WILL BE TAKING SHAPE IN THE CENTRAL GULF WHILE AN UPPER TROF MOVES ACROSS THE NORTHERN PLAINS. ASSOCIATED SURFACE COLD FRONT WILL CROSS THE MISSISSIPPI RIVER VALLEY LATE IN THE PERIOD SETTING UP ACTIVE WEATHER FOR THE REMAINDER OF THE WEEKEND INTO THE START OF THE WORK WEEK. TEMPERATURES THROUGH THE SHORT TERM PERIOD WILL BE ABOVE NORMAL AS HIGH PRESSURE SUBSIDENCE KEEPS SKY COVER LIMITED. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 225 AM EDT THURSDAY...MUCH UNCERTAINTY STILL REMAINS REGARDING DEVELOPING TROPICAL CYCLONE IN THE CENTRAL GULF. LATEST NHC GUIDANCE INDICATES A LARGE AREA OF CONVECTION NEAR THE YUCATAN PENINSULA WITH FLIGHT INFO FROM THE DISTURBANCE YIELDING INDICATIONS OF GALE FORCE WINDS...BUT NO CLOSED LOW AT THIS TIME. TROPICAL FORECAST MODELS CONTINUE TO CONVERGE THEIR SOLUTIONS ON A LOW TRACK THROUGH GEORGIA AND NORTHEAST ALONG AND JUST WEST OF THE I85 CORRIDOR BY MONDAY. OPERATIONAL MODELS SUCH AS THE GFS/ECMWF CONTINUE TO HAVE SLIGHT DIFFERENCES ON TIMING AND INTENSITY OF THIS SYSTEM...AND ITS INTERACTION WITH THE PROGRESSIVE UPPER TROF AND ASSOCIATED COLD FRONT THAT WILL BE MOVING THROUGH THE MISSISSIPPI RIVER VALLEY SATURDAY NIGHT THROUGH SUNDAY. THE GFS CONTINUES TO PRODUCE THE MOST IMPRESSIVE SOLUTION WITH A WELL DEFINED TROPICAL FEATURE MAKING LANDFALL ALONG THE FLORIDA PANHANDLE LATE ON SUNDAY NIGHT. AS THE UPPER TROF FEATURE CONTINUES EASTWARD...THE TROPICAL LOW LOOKS TO ACCELERATE OUT AHEAD CROSSING THE DEEP SOUTH INTO THE CAROLINAS BY MONDAY MORNING AS THE FROPA PUSHES INTO THE HIGHER TERRAIN. THE ECMWF HAS A WEAKER AND SLIGHTLY SLOWER SOLUTION THAN THE ABOVE MENTIONED GFS. EITHER WAY ITS TOO EARLY TO TELL WITH NEAR ABSOLUTE CERTAINTY WHERE THE TRACK OF THE TROPICAL LOW AND ITS ASSOCIATED MOISTURE WILL PASS. THIS TRACK WILL BE CRUCIAL TO DETERMINE THE APPROXIMATE THREATS ACROSS NORTHEAST GA AND THE CAROLINAS. AT THIS TIME USING A CONSENSUS OF TROPICAL MODEL OUTPUT BACKED UP BY THE OPERATIONAL GFS AND CMC...IT LOOKS AS IF THE PRIMARY THREATS WILL BE HEAVY RAINFALL WITH THE PRECIPITATION AXIS MAXIMIZED ALONG THE I85 CORRIDOR. A MARGINAL SEVERE THREAT REMAINS ACROSS AREAS EAST OF THE I85/I77 CORRIDORS WITH THIS CURRENT TRACK ON MONDAY. IF THE SYSTEM STARTS TO DEVELOP EXTRATROPICAL FEATURES AND BEGINS TO INTERACT MORE WITH THE FROPA...OR THE TRACK SHIFTS SLIGHTLY WEST...THE PRECIPITATION AXIS COULD SHIFT WESTWARD ALSO THEREBY INCREASING THE POTENTIAL FOR HEAVY RAINFALL ACROSS THE MOUNTAINS. AS FOR THE FCST...INCREASING POPS LATE ON SUNDAY NIGHT WILL EVENTUALLY SETUP SOLID LIKELY POPS ACROSS THE REGION ON MONDAY. TEMPERATURES WILL BE A FEW DEGREES BELOW NORMAL AS MOSTLY CLOUDY SKIES PREVAIL. BEHIND THE PASSING SYSTEM ON TUESDAY...THE GFS SOLUTION EJECTS THE TROPICAL LOW UP THE EAST COAST WITH THE COLD FRONT PROGRESSING OUT TO SEA. HIGH PRESSURE THEN BUILDS IN ACROSS THE EASTERN GREAT LAKES BY TUESDAY EVENING STRENGTHENING THROUGH MIDWEEK. THE ECMWF SOLUTION PLAYS OUT MUCH DIFFERENTLY WITH THE TROPICAL SYSTEM EJECTING AS IN THE GFS...YET THE SURFACE FRONT STALLS AS UPPER LEVEL RIDGING OVER THE WESTERN ATLANTIC HOLDS FIRM. AT THIS RANGE...WENT WITH A BLEND OF THE TWO SOLUTIONS THROUGH THE REMAINDER OF THE PERIOD YIELDING LOW END CHANCE POPS AND NEAR NORMAL TEMPERATURES FOR TUESDAY AND WEDNESDAY. && .AVIATION /11Z THURSDAY THROUGH MONDAY/... AT KCLT...MID AND HIGH CLOUDS ARE SHOWING SIGNS OF CLEARING FROM THE SOUTH AROUND DAYBREAK...AND SOME BRIEF FOG COULD STILL BE OBSERVED. WILL ONLY FEATURE TEMPO 6SM BR AT THIS POINT. CALM WINDS WILL GRADUALLY BECOME SOUTHERLY WITH MIXING BY LATE MORNING. ANY LINGERING HIGH CLOUDS SHOULD EVENTUALLY GIVE WAY TO SCT STRATOCUMULUS THROUGH THE DAY AS HEATING DEVELOPS. LIGHT S TO SW TO CALM WINDS WILL LINGER OVERNIGHT...WITH FEW STRATOCUMULUS...AND A LOW END THREAT OF MVFR FOG TOWARD DAYBREAK FRI. ELSEWHERE...FOG DEVELOPMENT REMAINS FAIRLY TRANSIENT THIS MORNING DUE TO THE PASSING MID AND HIGH CLOUDS ALOFT. ANTICIPATE THAT THE BEST CHANCE OF TEMPO IFR TO LIFR CIG OR VSBY WILL BE AT KAVL AND KAND THROUGH 14Z. OTHERWISE...LIGHT WINDS WILL BECOME SRLY THROUGH THE DAY...WITH HIGH CLOUDS GRADUALLY GIVING WAY TO SCT STRATOCUMULUS. ANY SPOTTY SHOWERS THROUGH THE DAY WILL BE CONFINED TO THE FAR WRN MTNS AND WILL NOT BE MENTIONED IN THE TAFS. VFR CONDITIONS WILL CONTINUE THROUGH THE EVENING HOURS WITH WINDS BECOMING LIGHT ONCE AGAIN. MVFR VSBY IN FOG IS LIKELY AT THE FOOTHILL TAFS OVERNIGHT...WITH IFR AT KAVL EARLY FRI MORNING. .OUTLOOK...SFC HIGH PRESSURE WILL LINGER THROUGH SAT. MOISTURE WILL INCREASE AHEAD OF AN APPROACHING COLD FRONT ON SUNDAY...WITH A TROPICAL WEATHER FEATURE POSSIBLY MOVING NWD FROM THE GULF OF MEXICO THROUGH MONDAY. THE BEST CHANCE OF WIDESPREAD RESTRICTIONS APPEARS TO BE SUNDAY NIGHT INTO MONDAY. CONFIDENCE TABLE... 11-17Z 17-23Z 23-05Z 05-11Z KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 100% KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAVL MED 65% HIGH 100% HIGH 100% HIGH 86% KHKY HIGH 100% HIGH 100% HIGH 100% HIGH 100% KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAND HIGH 93% HIGH 100% HIGH 100% HIGH 100% 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...CDG/HG NEAR TERM...HG SHORT TERM...CDG LONG TERM...CDG AVIATION...HG