Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 250145 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 945 PM EDT THU JUL 24 2014 .SYNOPSIS... A COLD FRONT WILL MOVE EAST OF THE AREA OVERNIGHT. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT FOR FRIDAY AND THE WEEKEND. ANOTHER COLD FRONT IS EXPECTED TO REACH THE AREA FROM THE NORTHWEST ON MONDAY. && .NEAR TERM /THROUGH FRIDAY/...
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AS OF 945 PM EDT...THE PASSING SFC COLD FRONT HAS MOVED TO NEAR THE INTERSTATE 85 CORRIDOR LATE THIS EVENING AND WILL CONTINUE TO PROGRESS SE OVERNIGHT. ANY LINGERING ISOLD SHOWERS THAT TRIGGER IN NW UPSLOPE FLOW INTO THE MTNS LATE THIS EVENING SHOULD DISSIPATE QUICKLY. GRADUAL DRYING WILL SET UP ON DEVELOPING N TO NE FLOW OVERNIGHT...HOWEVER...THE BOUNDARY LAYER WILL LIKELY SEE THE SLOWEST DRYING. THIS SHOULD LEAD TO LOW CLOUD FORMATION AND AT LEAST PATCHY FOG. THE AREAS THAT RECEIVED APPRECIABLE RAINFALL AS WELL AS THE MTN VALLEYS WILL STAND THE BEST CHANCE OF FOG DEVELOPMENT. LIGHT WINDS ARE EXPECTED TO VEER AROUND TO SE OR PERHAPS EVEN SRLY IN SRN SECTIONS THROUGH THE DAY ON FRIDAY. THE LIGHT UPSLOPE COMPONENT AND WEAKENING CAP MAY ALLOW FOR ISOLATED MOUNTAIN SHOWERS FRI AFTERNOON...BUT MOST LOCATIONS SHOULD BE DRY. MAX TEMPS WILL TOP OUT A COUPLE DEGREES BELOW CLIMO.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... AS OF 130 PM THU...UPPER HEIGHTS INITIALLY RISE FRI NIGHT AS A TROUGH LIFTS AWAY FROM THE EAST COAST...BUT REMAIN NEARLY STEADY THEREAFTER LEAVING OUR REGION UNDER SLIGHTLY CYCLONIC FLOW OVER THE WEEKEND. BY LATE SUNDAY HOWEVER HEIGHTS BEGIN TO FALL AGAIN AS ANOTHER SHORTWAVE DIGS INTO THE MIDWEST. AT THE SFC WEAK HIGH PRESSURE WILL PERSIST OVER THE SERN CONUS ALONG WITH LIGHT SWLY TO WLY FLOW. FOR SATURDAY THE MAIN DIFFICULTY IS TO DETERMINE WHETHER THE SFC HIGH WILL PROVIDE ENOUGH SUBSIDENCE TO STIFLE DIURNAL CONVECTION. MODELS DIFFER RATHER WIDELY IN THEIR DEPICTION OF THE CAP. 09Z SREF MEMBER SOUNDINGS MOSTLY SHOW A SIGNIFICANT MIDLEVEL INVERSION...BUT THE MEMBERS WHICH ARE UNCAPPED SHOW CAPE VALUES A BIT HIGHER THAN CLIMO GIVEN THE LACK OF RIDGING ALOFT. DRY MID-UPPER LEVELS AND LACK OF SHEAR IMPLY PULSE-MODE THREATS IF ANY CELLS ARE TO FIRE. ON THE OTHER HAND...GFS/GEFS IMPLY CAPPING AND ACCORDINGLY HAVE NO QPF RESPONSE. OVERALL SUPPORT SEEMS TO BE BETTER FOR A DRY FCST...THUS I HAVE MAINTAINED IT. HIGH TEMPS WILL BE ABOUT NORMAL FOR SATURDAY. THE POTENTIAL CAPPING IS A CRITICAL QUESTION FOR SUNDAY...BUT AT THAT TIME THERE IS THE ADDED ISSUE OF WHETHER THE COLD FRONT PLOWING ACRS THE OH/TN VALLEYS WILL HAVE ANY IMPACT DURING PEAK HEATING. EARLIER MODEL RUNS SUGGESTED THE FRONT WOULD BE NEAR ENOUGH TO PUT OUR AREA IN A MORE FAVORABLE ENVIRONMENT FOR STRONG STORMS SUNDAY AFTN...BUT LATEST GUIDANCE HAS DELAYED IT AND A FAIR NUMBER OF THE LATEST RUNS AGAIN KEEP CONVECTION TO A MINIMUM OVER THE CWFA. ENSEMBLE SOLUTIONS LEND SOME SUPPORT THOUGH...AND IN LIGHT OF THE UNCERTAIN MODEL TRENDS AND CONTINUED EXPECTATION THAT THE FRONT WILL BE NEARBY...LOW POPS HAVE BEEN KEPT SUNDAY AFTN...RAMPING UP INTO SUNDAY NIGHT. TEMPS WILL INCH UP SLIGHTLY FURTHER SUNDAY UNDER HIGHER THICKNESSES IN THE SWLY FLOW. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 150 PM THURSDAY...SUBSTANTIAL/ANOMALOUSLY STRONG UPPER HEIGHT FALLS WILL BE INTRODUCED TO THE EASTERN CONUS EARLY IN THE MEDIUM RANGE PERIOD...ALLOWING A COLD FRONT TO PUSH TOWARD THE REGION. THE LATEST GLOBAL MODEL RUNS HAVE CONTINUED A RECENT TREND OF DRIER PRE-FRONTAL AIR AND A WEAKER QPF RESPONSE WITH THE FRONT IN THE LATE SUNDAY NIGHT/EARLY MONDAY TIME FRAME. IN FACT...A CONSENSUS SEEMS TO BE DEVELOPING THAT PROBABILITIES FOR SHOWERS WILL BE VERY LOW... EXCEPT PERHAPS ACROSS THE SOUTHERN AND EASTERN FRINGE OF OUR PIEDMONT AREAS MON AFTERNOON...WHEN THE FRONT WILL HAVE A LITTLE MORE IN THE WAY OF BUOYANCY TO WORK WITH. NEVERTHELESS...EARLY NEXT WEEK IS STILL TOO FAR IN THE FUTURE FOR US TO GET TOO CUTE WITH TIMING THE POSITION OF THE FRONT...AND THESE SCENARIOS TYPICALLY EVOLVE MORE SLOWLY THAN ADVERTISED BY THE MODELS THIS TIME OF YEAR. THEREFORE...WILL GENERALLY FEATURE A SHOTGUNNED CHANCE POP ACROSS THE CWFA THROUGHOUT MONDAY...DIMINISHING TO SLIGHT CHANCE OR LESS BY EVENING. THE REMAINDER OF THE FORECAST PERIODS LOOKS VERY SIMILAR TO WHAT WAS EXPERIENCED ABOUT A WEEK AGO...WHEN AN UNUSUALLY COOL/DRY AIR MASS BECAME ESTABLISHED OVER THE REGION UNDERNEATH AN ANOMALOUSLY STRONG EASTERN TROUGH. IF ANYTHING...THIS AIR MASS PAY PROVE TO BE A LITTLE MORE PERSISTENT THAN LAST WEEK/S. TEMPS ARE EXPECTED TO BE 5-10 DEGREES BELOW CLIMO THROUGH THE PERIOD...WHILE A HALT IN DIURNAL CONVECTION IS EXPECTED THROUGH AT LEAST WED. BY THE END OF THE PERIOD...THERE ARE SIGNS THAT...AGAIN SIMILAR TO LAST WEEK/S EVENTS...THE TROUGH WILL EFFECTIVELY RETROGRADE... ALLOWING MOISTURE TO RETURN WITHIN A DEVELOPING WEDGE-LIKE SCENARIO. POPS AND CLOUDS WILL THEREFORE BEGIN TO INCREASE BY THE END OF THE PERIOD...WITH TEMPS REMAINING COOL WITHIN A DEVELOPING EASTERLY LOW LEVEL FLOW REGIME. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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AT KCLT...ALL CONVECTION HAS MOVED EAST OF KCLT AND WANED THIS EVENING. ANTICIPATE VFR CONDITIONS THROUGH LATE EVENING AND EARLY OVERNIGHT...WITH NW WINDS TURNING MORE NRLY AND THEN NE OVERNIGHT POST FROPA. THE BOUNDAY LAYER WILL STAY MOIST...HOWEVER...AND RECENT RAINFALL WILL CONTRIBUTE TO LOW STRATUS AND FOG DEVELOPMENT IN THE PIEDMONT. THERE IS GROWING CONSENSUS FOR IFR CIGS DURING THE EARLY MORNING HOURS...BUT IT MAY BATTLE WEAK NRLY WIND AND DRYING. HAVE COMPROMISED BY EDGING THE FORECAST CLOSER TO IFR WITH BKN010 LATE TONIGHT. EXPECT QUICK IMPROVEMENT BY 14Z...WITH VFR CONDITIONS AND LIGHT ENE WINDS...POSSIBLY TOGGLING SE LATE DAY. ELSEWHERE...PRECIPITATION HAS ENDED ACROSS THE MTN AND FOOTHILL TAF SITES THIS EVENING. ANY RESIDUAL UPSLOPE INDUCED SHOWERS ALONG THE SPINE OF THE MOUNTAINS SHOULD DISSIPATE BEFORE REACHING KAVL. THE MOIST BOUNDARY LAYER COULD WELL LEAD TO LOW CLOUD AND FOG FORMATION DURING THE EARLY MORNING HOURS. THE BEST CHANCE OF THIS WILL BE AT KAVL...BUT WILL HINT AT SOME FEW TO SCT010 AT THE FOOTHILL SITES...AND FORECAST IFR VSBY AT KHKY OVERNIGHT. THE LOW RESTRICTIONS SHOULD DISSIPATE QUICKLY BY 14Z FRI MORNING...WITH MAINLY SCT VFR CLOUDS THROUGH THE DAY ALONG WITH E TO SE WINDS...EXCEPT SW FROM KAND TO KAVL DURING THE AFTN. OUTLOOK...FRI NIGHT THROUGH SUNDAY MORNING SHOULD BE QUIET AND VFR...EXCEPT FOR THE MTN VALLEYS WHERE EARLY MORNING FOG MAY OCCUR. SCT THUNDERSTORMS MAY RETURN TO THE FORECAST AREA FOR SUNDAY AFTERNOON...THOUGH MORE LIKELY MON...AS ANOTHER COLD FRONT APPROACHES AND THEN MOVES THROUGH THE AREA BY MON NIGHT. CONFIDENCE TABLE... 01-07Z 07-13Z 13-19Z 19-01Z KCLT HIGH 100% HIGH 83% HIGH 95% HIGH 100% KGSP HIGH 100% HIGH 95% HIGH 100% HIGH 100% KAVL HIGH 90% MED 73% HIGH 100% HIGH 100% KHKY HIGH 100% HIGH 94% HIGH 100% HIGH 100% KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAND HIGH 100% HIGH 85% 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
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...LG NEAR TERM...HG SHORT TERM...WIMBERLEY LONG TERM...JDL AVIATION...HG

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