Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 150730 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 330 AM EDT MON SEP 15 2014 .SYNOPSIS... COOL BUT UNSETTLED WEATHER WILL CONTINUE THROUGH TONIGHT...AS A STATIONARY FRONT WILL REMAIN JUST TO OUR SOUTH BEFORE AN UPPER DISTURBANCE PASSES THROUGH. A COLD FRONT WILL THEN CROSS THE AREA IN ITS WAKE...USHERING IN SEASONABLY COOL AIR AND MOSTLY DRY WEATHER LASTING INTO THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS WEAKENING HIGH PRESSURE RIDGE SLIDES OFF THE COAST TODAY (ESSENTIALLY ENDING THE PERIOD OF NE FLOW)...AND THE FLOW ABOVE THE SURFACE LAYER TURNS TO LIGHT WESTERLY...LOW CLOUDS SHOULD LIFT AND POSSIBLY SCATTER AT TIMES LATER TODAY. THIS WILL ALLOW TEMPS TO REBOUND TO 75-80 ACROSS MUCH OF THE AREA THIS AFTERNOON...WHICH IS STILL A FEW DEGREES SHY OF CLIMO. THE ADDITIONAL HEATING SHOULD ALLOW THE ATMOSPHERE TO DESTABILIZE MODESTLY THIS AFTERNOON. COMBINED WITH PWATS THAT REMAIN QUITE JUICY FOR THE TIME OF YEAR...ISLD TO WIDELY SCT CONVECTION SHOULD DEVELOP BY MID-AFTERNOON ACROSS WESTERN AREAS...ESP ACROSS THE HIGH TERRAIN AND UPPER SAVANNAH RIVER VALLEY...WHERE INSTABILITY SHOULD BE GREATEST. THE SHORT TERM MODELS KICK A WEAK SHORT WAVE TROUGH...CURRENTLY SEEN AS A SUBTLE FEATURE IN WV IMAGERY OVER NW TEXAS...OVER THE SOUTHEAST LATER TODAY...WHICH SUPPORTS QUITE A BIT OF CONVECTIVE DEVELOPMENT OVER THE TENN VALLEY/NORTH GA BY LATE AFTERNOON. THIS ACTIVITY SHOULD MAKE A RUN TOWARD...AND/OR INITIATE NEW CONVECTION OVER OUR AREA BY EVENING...AND THIS IS WHEN POPS REACH A NADIR. THE HIGHEST POPS...GENERALLY 40-50 PERCENT WILL BE FAVORED OVER THE UPSTATE AND NORTHEAST GEORGIA...WHICH SHOULD SEE THE MOST FAVORABLE JUXTAPOSITION OF DEEP MOISTURE/INSTABILITY/FORCING. WHILE SHEAR WILL BE SOMEWHAT RESPECTABLE FOR THE TIME OF YEAR...CURRENT INDICATIONS ARE THAT PROFILES WILL BE TOO MOIST AND INSTABILITY TOO LIMITED TO SUPPORT MUCH OF A SEVERE WEATHER THREAT. ADDITIONALLY... UNIDIRECTIONAL WIND PROFILES SHOULD SUPPORT PROGRESSIVE CELL MOVEMENT...SO EVEN THE HEAVY RAIN/FLASH FLOOD THREAT APPEARS TO BE LOW. COLD FRONT ASSOCIATED WITH POTENT SHORT WAVE TROUGH TRAVERSING THE GREAT LAKES REGION IS EXPECTED TO ENTER THE CWA BY DAYBREAK... SUPPORTING AT LEAST LOW POPS THROUGH THE OVERNIGHT. MIN TEMPS ARE EXPECTED TO BE SLIGHTLY ABOVE CLIMO. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM MONDAY...UPPER PATTERN WILL GRADUALLY AMPLIFY OVER THE CONUS THRU THE MIDWEEK EVENTUALLY LEADING TO DEEPER TROUGHING OVER THE EAST. A WEAK AREA OF HIGH PRESSURE WILL MOVE EWD OUT OF THE PLAINS TUE AND TUE NIGHT. A WEAK COLD FRONT AHEAD OF THIS HIGH WILL WORK THROUGH OUR CWFA TUESDAY...WITH THE HIGH PRESSURE SLOWLY SHIFTING ACRS THE MTNS BY WED AND PRODUCING WEDGELIKE EASTERLY FLOW INTO THE AREA. MOISTURE IS NOT THAT IMPRESSIVE THROUGH THE COLUMN AT ANY TIME DURING THE PERIOD...WITH INSTABILITY THE MAIN JUSTIFICATION FOR POPS. THOUGH POOR MIDLEVEL LAPSE RATES ARE EXPECTED...THE PERSISTENT CYCLONIC FLOW ALOFT IS SUGGESTED TO FORCE A LEE TROUGH TUE AFTN...AND BRING EDDIES ACRS THE FA BOTH TUE AND WED NIGHTS. CONTINUOUS LOW POPS WILL BE ADVERTISED WITH MINOR INCREASES WHEN ENHANCED FORCING IS PRESENT. THE COOLER AIR WILL TAKE SOME TIME TO FILTER IN...AND ESP WITH DOWNSLOPING TUE MAX TEMPS WILL RISE A TAD ABOVE CLIMO. WED MAXES AND WED NIGHT MINS WILL BE A CATEGORY OR TWO BELOW CLIMO WITHIN THE POST-FRONTAL AIRMASS. IT SHOULD BE NOTED THAT THE NAM DEVELOPS MUCH MORE INSTABILITY TUE AFTN THAN THE GFS BUT KEEPS SFC PARCELS SLIGHTLY CAPPED DUE TO THE AFOREMENTIONED POOR LAPSE RATES ATOP THE MIXED LAYER. THOUGH ONLY ISOLATED CELLS ARE EXPECTED TO BE ABLE TO FORM...0-6KM BULK SHEAR VALUES WILL BE A BIT STRONGER THAN WHAT WE/VE SEEN LATELY. ACTIVITY FORMING DURING PEAK HEATING MAY POSE A SMALL SEVERE RISK IF IT GROWS TALL ENOUGH. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 230 AM MONDAY...AN INITIALLY SIMPLE WESTERN RIDGE/EASTERN TROUGH PATTERN THURSDAY WILL BECOME MORE COMPLEX OVER THE WEEKEND WITH REASONABLE AGREEMENT BETWEEN THE 15/00Z GFS AND 14/12Z EC AS TO ITS EVOLUTION. THE ERN TROUGH PROGRESSES ENOUGH TO ALLOW REAL COLD AIR DAMMING TO FORM BY FRI MRNG...REINFORCING SEASONABLY COOL TEMPS FOR THE REGION AND SUPPORTING A DRY FCST THRU MOST OF THE WEEKEND. WEAK UPPER RIDGING RETURNS TO THE SOUTHEAST SATURDAY AS THE PARENT HIGH IS PUSHED OFFSHORE. THIS IN CONJUNCTION WITH LOW PRESSURE MOVING ALONG THE CANADIAN BORDER INITIATES RETURN FLOW SUNDAY...WEAKENING THE WEDGE AND ALLOWING A BRIEF WARMUP. THAT LOW DOES THEN BRING ANOTHER COLD FRONT INTO OUR AREA TO START THE NEW WEEK. GFS IS MORE BULLISH WITH THE FRONT AS IT DEVELOPS A SECONDARY SFC LOW OVER THE MIDWEST IN RESPONSE TO A SHORTWAVE EMBEDDED IN THE SYNOPTIC FLOW. THE 15/00Z EC JUST ARRIVED STILL FAVORING THE PREVIOUS RUN/S TRACK OF THE CANADIAN LOW...BUT AMPLIFIES THE UPPER TROUGH SUBSTANTIALLY. THIS BACKS UP A STRONGER FROPA FOR EARLY MONDAY. EITHER WAY IT LOOKS LIKE EVEN COOLER WEATHER IS IN STORE NEXT WEEK. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... AT KCLT...THE PRIMARY CONCERN SURROUNDS JUST HOW MUCH CIGS WILL LOWER THIS MORNING. CONDITIONS ARE SOLIDLY MVFR AS OF 0530Z...BUT NE FLOW JUST ABOVE THE SURFACE INDICATES SOME SLIGHTLY DRIER AIR IS FILTERING INTO THE REGION. ON THE OTHER HAND...NEAR TERM MODEL GUIDANCE IS IN AGREEMENT THAT THE FLOW WILL TURN TOWARD THE SW TOWARD DAYBREAK...WHICH WOULD STOP ANY DRY AIR INFILTRATION AND POSSIBLY ALLOW CIGS TO LOWER TO IFR. IN FACT...I THINK THERE/S ENOUGH POTENTIAL FOR THIS TO INCLUDE A TEMPO BETWEEN 10Z AND 12Z. SOME BR IN THE 5-6SM RANGE WILL ALSO BE POSSIBLE. OTHERWISE...CIGS SHOULD LIFT TO VFR BY EARLY AFTERNOON...AND POSSIBLY SCATTER FROM TIME TO TIME. AN UPPER AIR DISTURBANCE WILL BRING INCREASING CHANCES FOR CONVECTION DURING THE EVENING...MAINLY IN THE FORM OF SHRA. A PROB30 HAS BEE INTRODUCED TO ACCOUNT FOR THIS. LGT/VRBL WINDS SHOULD BECOME LIGHT SW BY MID-AFTERNOON. ELSEWHERE...OUR BEST PERFORMING GUIDANCE OVER THE PAST COUPLE OF DAYS IS INSISTENT IN DEVELOPING LIFR (AT KAVL) AND IFR (ELSEWHERE) CIGS WITHIN THE NEXT COUPLE OF HOURS...AND HAS PLENTY OF SUPPORT FROM OTHER RELIABLE GUIDANCE. HOWEVER...CIGS HAVE ACTUALLY BEEN SLOWLY LIFTING OVER THE PAST COUPLE OF HOURS. THERE IS ALSO INDICATION THAT THE FLOW WILL VEER TOWARD THE W/SW ABOVE THE SURFACE (ALBEIT REMAINING LIGHT) TOWARD DAYBREAK...RESULTING IN AN INCREASED DOWNSLOPE COMPONENT WHICH WOULD BE A LIMITING FACTOR FOR CIGS LOWERING MUCH FURTHER. NEVERTHELESS...WE ARE STARTING TO SEE PATCHY FEW/SCT IFR CLOUDS SHOWING UP ON AREA METARS...SO TEMPOS FOR IFR HAVE BEEN ADDED FOR AT LEAST A COUPLE OF HOURS THROUGH DAYBREAK. KHKY SEES THE SHORTEST TEMPO (2 HOURS) DUE TO STRONGER EFFECTS FROM DOWNSLOPING. MEANWHILE...KAVL IS ALREADY LIFR AND SHOULD REMAIN SO THE REST OF THE NIGHT...ALTHOUGH WOULD NOT BE SURPRISED TO SEE THEM VARY QUITE A BIT...ES ONCE THE W/SW FLOW BECOMES ESTABLISHED. AN UPPER AIR DISTURBANCE WILL BRING INCREASING CHANCES FOR CONVECTION TO WESTERN AREAS BY LATE AFTERNOON...CONTINUING THROUGH THE END OF THE PERIOD. A PROB30 FOR TSRA HAS BEEN INTRODUCED TO ACCOUNT FOR THIS. OUTLOOK...SCT SHOWERS/THUNDERSTORMS WILL CONTINUE INTO EARLY TUE... WHILE FLT RESTRICTIONS MAY DEVELOP AGAIN TUE MORNING IN LOW CLOUDS AND/OR FOG. A RETURN TO MAINLY VFR CONDITIONS IS EXPECTED LATER TUE INTO MIDWEEK OUTSIDE OF RESTRICTIONS WITH DIURNAL CONVECTION. CONFIDENCE TABLE... 07-13Z 13-19Z 19-01Z 01-07Z KCLT MED 75% HIGH 87% HIGH 100% HIGH 100% KGSP MED 64% HIGH 81% HIGH 84% HIGH 100% KAVL MED 75% HIGH 80% HIGH 90% HIGH 85% KHKY MED 61% MED 79% HIGH 98% HIGH 94% KGMU LOW 56% HIGH 81% HIGH 87% HIGH 100% KAND HIGH 85% HIGH 91% 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...WIMBERLEY NEAR TERM...JDL SHORT TERM...WIMBERLEY LONG TERM...WIMBERLEY AVIATION...JDL

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