Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 202352 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 752 PM EDT WED AUG 20 2014 .SYNOPSIS... A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD ACROSS THE MISSISSIPPI RIVER VALLEY OVER THE NEXT FEW DAYS AND LINGER FOR THE REST OF THE WORK WEEK...RESULTING IN ABOVE NORMAL TEMPERATURES. A WEAK COLD FRONT WILL THEN PUSH INTO THE AREA FROM NORTHEAST SATURDAY AND BRING SOME MINOR RELIEF FROM THE HEAT. && .NEAR TERM /THROUGH THURSDAY/... AS OF 750 PM...CONVECTION ACROSS THE CWFA QUICKLY DISSIPATING WITH LOSS OF HEATING. ADDITIONAL CONVECTION OVER E TN SHOWS SOME SIGNS OF WEAKENING...BUT COVERAGE REMAINS UNCHANGED. HAVE UPDATED POP TO QUICKLY FALL OFF ACROSS THE UPSTATE AND NE GA...BUT SCT POP TO RETURN THIS EVENING ACROSS THE MTNS AS THE CONVECTION MOVES IN FROM TN. CANNOT RULE OUT A FEW SVR STORMS ACROSS THE MTNS OVERNIGHT...BUT CHC IS QUICKLY DIMINISHING. QUITE A BIT OF DEBRIS CLOUDS LINGER OVER THE WRN CWFA WITH MOSTLY CLEAR SKIES EAST. THE DEBRIS CLOUDS WILL CONTINUE OVERNIGHT...BUT SHUD THIN OUT WITH TIME. STILL EXPECT PATCHY FOG OVERNIGHT...WITH BEST CHC IN THE MTN VALLEYS. AS OF 425 PM...CLUSTER OF TSRA ASSOCIATED WITH THE PREVIOUS MCS HAVE FINALLY DISSIPATED AS THEY MOVED SOUTH OF THE CWFA. ADDITIONAL STORMS ARE FORMING ACROSS THE MTNS AHEAD OF ANOTHER SHORTWAVE. THESE STORMS WILL MOVE SOUTH INTO THE UPSTATE AND NE GA...AND ACROSS THE NC MTNS THRU THE AFTERNOON AND POSSIBLY INTO THE EARLY EVENING... ESPECIALLY ACROSS THE NC MTNS. WITH THE AMOUNT OF INSTABILITY AND DCAPE VALUES OVER THE AREA...CANNOT RULE OUT ADDITIONAL SEVERE STORMS. HAVE UPDATED POP TO INCLUDE THESE FEATURES. OTHERWISE... UPDATES FOR CURRENT CONDITIONS. PREVIOUS DISCUSSION...A PERSISTENT SMALL/STRONG TO OCCASIONALLY SEVERE CONVECTIVE CLUSTER CONTINUES TO DROP SOUTHEAST TOWARD SPARTANBURG COUNTY. SCT CONVECTION IS FINALLY BEGINNING TO UNZIP A BIT ALONG THE OUTFLOW BOUNDARY ALONG THE I-40 CORRIDOR INTO THE NC PIEDMONT. OTHERWISE... THE LATEST SPC MESOANALYSIS DEPICTS A MINIMA IN CAPE ACROSS THE AREA...WITH CAPE EXCEEDING 3000 J/KG JUST TO OUR EAST... AND MORE THAN 4000 J/KG ACROSS EAST TENN INTO NRN/CTRL GEORGIA. OTHER THAN FEATURING 40-60 POPS DOWNSTREAM OF THE ONGOING ACTIVITY...THE HIGHEST POPS HAVE BEEN DELAYED UNTIL EVENING ACROSS WESTERN AREAS. ROBUST CONVECTION IS DEVELOPING WITHIN THE VERY UNSTABLE AIR ACROSS EAST TENN...AND IT APPEARS COVERAGE WILL ONLY INCREASE THERE THROUGH THE AFTERNOON...WITH SOME UPSCALE GROWTH POSSIBLE IF NOT LIKELY IN LIGHT OF 0-3KM SHEAR OF AROUND 20 KTS. WE HAVE THEREFORE INCREASED POPS TO LIKELY THIS EVENING ACROSS THE SOUTHWEST MTNS OF NC. BRIEF LARGE HAIL AND DAMAGING WINDS WILL REMAIN POSSIBLE...WITH DOWNBURST POTENTIAL ENHANCED WITH ANY ORGANIZED CLUSTERS. CONVECTION SHOULD WANE AND/OR PUSH SOUTH OF THE FORECAST AREA BY LATE EVENING. HOWEVER...LOW CHANCE POPS WILL BE MAINTAINED ACROSS THE FAR WESTERN MTNS...ESP THE NORTHERN MTNS...AS ADDITIONAL SHORT WAVE TROUGHS AND/OR MCV/S DROPPING SOUTHEAST...DOWNSTREAM OF BUILDING UPPER RIDGE WILL CONTINUE TO CLIP THE FORECAST AREA. OTHERWISE...UPPER HEIGHTS WILL CONTINUE TO BUILD ACROSS THE SOUTHEAST INTO THURSDAY...RESULTING IN WARMER MID-LEVEL TEMPS AND A DEEPER/RELATIVELY DRIER BOUNDARY LAYER WITH HIGHER LFC/S. NEVERTHELESS...FORECAST SOUNDINGS ARE LARGELY UNCAPPED AND QUITE UNSTABLE BY AFTERNOON. POPS WILL BE ADVERTISED NEAR-CLIMO...WITH SLIGHT/LOW CHANCE POPS OUTSIDE THE MTNS...AND CHANCES OVER THE HIGH TERRAIN. TEMPS WILL BE A BIT ABOVE NORMAL THROUGH THE PERIOD. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... AS OF 255 PM EDT WEDNESDAY... THE UPPER RIDGE CURRENTLY IN PLACE FROM THE WESTERN GULF OF MEXICO TO THE NORTHERN PLAINS...WILL RETROGRADE OR BECOME SLIGHTLY RE-ORIENTED BY SATURDAY. MEANWHILE THE UPPER LOW PIN-WHEELING ACROSS THE GREAT LAKES...WILL DRIFT TOWARD THE NEW ENGLAND COAST. THEREFORE SENSIBLE WEATHER IN THE SHORT TERM SUGGESTS A CONTINUOUS FLOW OF S/W`S WILL SLIDE SEWD (IN THE NWLY FLOW ALOFT) TOWARD OUR REGION THIS PERIOD. IT APPEARS ONE SUCH S/W COULD CLIP PARTS OF THE NORTHERN AND EASTERN SECTIONS OF OUR FORECAST AREA THURSDAY NIGHT. THEREFORE...AFTER SOME THURSDAY EVENING NC POPS FOR UPSLOPING ON THE WEST FACING SLOPES...WE WILL ADJUST POPS ACROSS OUR NRN AND ERN COUNTIES FOR CHANCE OF SHOWERS AND THUNDERSTORMS OVERNIGHT. OTHER THEN RIDGE TOP STORMS FRIDAY...IT IS HARD TO NAIL DOWN ANY OTHER AREA FOR HIGHER POPS...ALTHOUGH FLOW ALOFT SUGGESTS OUR NRN SECTIONS MAY HAVE A BETTER CHANCE. WITH MOISTURE AND INSTABILITY IN PLACE WILL CARRY CHANCE IN THE NORTH AND SLIGHT CHANCE SOUTHERN SECTIONS. IT APPEARS A BACK DOOR COLD FRONT WILL EDGE TOWARD THE REGION SATURDAY WITH MORE CLOUD COVER...AND PERHAPS AN INCREASE IN OVERALL PRECIPITATION POTENTIAL. WE HAVE NOT GONE OVERBOARD YET TO SEE IF THE TREND CONTINUES DURING THIS TIME-FRAME. GUIDE TEMPERATURES ON FRIDAY SHOULD BE VERY WARM OR HOT...WITH APPARENT TEMPERATURES CLIMBING TO 100 DEGREES OR BETTER IN OUR SC PIEDMONT ZONES. WE HAVE USED MORE OF A CONSENSUS OF TEMPERATURES... RATHER THAN MOS VALUE GUIDE ON FRIDAY AND SATURDAY. TEMPERATURE TREND AS MENTIONED HOT ON FRIDAY...BUT KNOCKED BACK SOMEWHAT ON SATURDAY...BECAUSE OF CLOUDS AND POTENTIAL PRECIPITATION. THERMAL PROFILE ALSO SUGGESTS THIS PLAN. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... AS OF 1230 PM WEDNESDAY...MEDIUM RANGE MODELS ARE IN DECENT ENUF AGREEMENT WITH RESPECT TO THE MEAN PATTERN FOR THE FIRST HALF OF THE EXTENDED PERIOD FEATURING LLVL RIDGING POKING SSW INTO THE CWFA. THE COMBINATION OF THE LLVL EASTERLY FLOW AND THE HIGHLY AMPLIFIED NLY FLOW SHOULD RESULT IN ENUF FORCING FOR AT LEAST SCATTERED SHOWERS...AND MAX TEMPERATURES A FEW DEG F BELOW PERSISTANCE AND A CATEGORY OR TWO BELOW CLIMO SUNDAY AND MONDAY. WITH LLVL RIDGING LIKELY TO LINGER THRU TUESDAY...THERE REMAINS ABOVE NORMAL CONFIDENCE THAT MAXIMUM TEMPERATURES WILL CONTINUE TO AVERAGE BELOW CLIMO. IT REMAINS TO BE SEEN ON JUST HOW MUCH FORCING IS AVAILABLE TO TRIGGER SHOWER ACTIVITY...SO JUST A TOKEN SLIGHT AND/OR SMALL POP WILL REMAIN. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... AT KCLT...CONVECTION SHOULD REMAIN NORTH AND WEST OF THE AIRFIELD OVERNIGHT EVEN IF IT SURVIVES THE TRIP OVER THE MTNS. WINDS HAVE BEEN TRICKY WITH ALL INDICATIONS THEY WOULD BE WNW...BUT HAVE REMAINED WSW. WILL KEEP THE WSW THIS EVENING...THEN CALM OVERNIGHT. LIGHT NLY WIND DEVELOPS AFTER DAYBREAK...THEN TURNS WNW FOR THE AFTERNOON. ANY CLOUDS SHOULD REMAIN VFR THRU THE PERIOD. CONVECTION IS EXPECTED AGAIN THU. HOWEVER...CELLS SHOULD REMAIN NORTH AND WEST OF THE AIRFIELD. ELSEWHERE...CONVECTION DISSIPATING ACROSS THE UPSTATE BUT STILL GOING STRONG ACROSS E TN. WILL HAVE TO WATCH KAVL FOR ANY AMD OVERNIGHT IF THE CONVECTION CAN SURVIVE THE TRIP ACROSS THE HIGHEST ELEVATIONS. RELIABLE GUIDANCE IS ONCE AGAIN HITTING THE FOG HARD LATE TONIGHT...AS IT HAS BEEN DOING THE PASTS SEVERAL MORNINGS... WITH VERY POOR VERIFICATION RESULTS. THEREFORE...HAVE IMPROVED THE VSBY FORECAST CONSIDERABLY OVER WHAT GUIDANCE IS ADVERTISING...BUT THIS IS STILL RESULTING IN A 3SM FORECAST AT KAVL. EXPECT ANOTHER ROUND OF CONVECTION THU...WITH BEST CHC OVER THE MTNS AND I-40 CORRIDOR...SO INCLUDED PROB30 FOR KAVL/KHKY. CHC TOO LOW ELSEWHERE. OTHERWISE...VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD OUTSIDE OF SHRA/TSRA. OUTLOOK...SCT AFTERNOON CONVECTION AND PATCHY EARLY MORNING FOG WILL REMAIN IN THE FORECAST THROUGH THE WEEK. THERE WILL ALSO BE AN OUTSIDE CHANCE FOR REMNANT ORGANIZED CONVECTION APPROACHING THE AREA FROM THE NW DURING THE LATE NIGHT/EARLY MORNING HOURS. CONFIDENCE TABLE... 00-06Z 06-12Z 12-18Z 18-24Z KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 100% KGSP HIGH 100% HIGH 100% HIGH 97% HIGH 100% KAVL HIGH 94% HIGH 88% HIGH 94% HIGH 100% KHKY HIGH 100% HIGH 94% HIGH 91% HIGH 100% KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAND HIGH 100% HIGH 94% HIGH 91% 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...CSH NEAR TERM...JDL/RWH SHORT TERM...TS LONG TERM...CSH AVIATION...RWH

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