Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 042049 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 449 PM EDT FRI SEP 4 2015 .SYNOPSIS... A COOL AND MOIST WIND FLOW OFF THE ATLANTIC THIS WEEKEND WILL KEEP CONSIDERABLE CLOUDINESS AND COOLER TEMPERATURES FOR OUR REGION. EXPECT GRADUAL WARMING EARLY TO MIDDLE OF THE UPCOMING WEEK UNDER AN UPPER RIDGE. A COLD FRONT AND UPPER TROUGH WILL ARRIVE AT THE END OF THE WEEK. && .NEAR TERM /THROUGH SATURDAY/... AS OF 430 PM...MADE SOME UPDATES TO SKY/POPS/WX BASED ON CURRENT TRENDS. SEEING SOME NON-SEVERE DOWNBURSTS WITH THESE STORMS... ESPECIALLY WITH THE AID OF THE TCLT TDWR. ISOLATED SEVERE STILL DEFINITELY POSSIBLE...HAVE SEEN SOME REPORTS OF SEVERE WINDS AND HAIL TO OUR SOUTH WHERE CAPE/DCAPE VALUES ARE A LITTLE HIGHER. TRENDS INTO THE EVENING STILL LOOK GOOD BUT WILL UPDATE AS NECESSARY THROUGH THE EVENING. AS OF 230 PM...SATELLITE IMAGERY SHOWS ENHANCED CU OVER THE RIDGETOPS AND RADAR IMAGERY SHOWS THAT DEEP CONVECTION HAS INITIATED ACROSS PARTS OF NC AND ALONG THE BLUE RIDGE IN VA...AND DOWN ACROSS THE AREA NEAR THE FALL LINE. COVERAGE SHOULD GRADUALLY EXPAND FROM THERE. STILL THINK WE COULD SEE A FEW STORMS BECOME STRONG ENUF TO PRODUCE DAMAGING WIND GUSTS NOW THAT WE HAVE REALIZED THE EXPECTED ENVIRONMENT WITH DCAPE 1000+ J/KG. TEMPS LOOK GOOD. THE NEXT 24 HOURS SHOULD SEE THE DEVELOPMENT OF A PSEUDO-WEDGE-LIKE SCENARIO ACROSS THE WESTERN CAROLINAS. THE UPPER AIR PATTERN REMAINS CONVOLUTED WITH AN OVERALL HIGH AMPLITUDE RIDGE ACROSS EASTERN NORTH AMERICA...BUT WITH AN UPPER LOW CENTERED OFF THE SOUTHEAST COAST AND WEAK CYCLONIC FLOW AT MID LEVELS ACROSS THE FCST AREA. WITHIN THIS FLOW...A LARGE SURFACE HIGH WILL BE SUPPORTED TO OUR NE...LOOSELY ANCHORED OVER NEW ENGLAND AND THE MARITIME PROVINCES. WHAT THIS DOES IS PROVIDE A LOW LEVEL NE FLOW...WHICH IS NOT REALLY DAMMED ACROSS THE AREA TO OUR N. HOWEVER...THE EASTERLY FLOW AND THE DEVELOPMENT OF CONVECTIVE PRECIP ACROSS THE PIEDMONT AND FOOTHILLS OF VA AND NRN NC MAY FORM A COOL POOL THAT OOZES SOUTH AND SOUTHWESTWARD OVERNIGHT...PERHAPS ALONG CONVECTIVE OUTFLOWS. THIS IN EFFECT WILL FORM A SORT OF IN-SITU WEDGE INTO THE FCST AREA...WHICH SHOULD GRADUALLY PUSH S AND SW INTO SATURDAY MORNING. THE PROBLEM IS THE E/NE FLOW IS FAIRLY DEEP AND THERE WILL NOT BE ANY ISENTROPIC LIFT OR LLVL WARM ADVECTION OVER THE TOP OF A STABLE BOUNDARY LAYER TO MAINTAIN IT. AS A RESULT...ON SATURDAY WE ARE LEFT WITH BASICALLY A COOL AND CLOUDY NE FLOW NEAR THE SFC. THE MODELS PUSH PRECIP PRODUCTION DOWN INTO NE GEORGIA AND ACROSS THE MTNS BY AFTERNOON. WILL HEDGE AND KEEP AT LEAST A SLIGHT CHC OVER THE WRN NC PIEDMONT. THIS WILL MAKE THE HIGH TEMP FCST TRICKY. NOT CONVINCED TEMPS WILL REMAIN BELOW GUIDANCE...SO HAVE NUDGED THEM UP A BIT OVER THE PIEDMONT. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... AS OF 200 PM FRI...LITTLE IMPACTFUL CHANGE IS EXPECTED IN THE OVERALL SFC/UPPER PATTERN OVER THE PERIOD. HIGH PRESSURE OVER THE NE CONUS WILL WEAKEN SLOWLY AND MOVE OFFSHORE UNDER THE INFLUENCE OF FALLING HEIGHTS OVER THE MIDWEST. NORTHEASTERLY TO EASTERLY FLOW WILL CONTINUE INTO THE CAROLINAS ON THE SRN PERIPHERY OF THE HIGH. THE MAIN EFFECT WILL BE TO MAINTAIN LOW TO MID LEVEL MOISTURE TRANSPORT FROM THE ATLANTIC...BUT ONLY SLIGHT UPSLOPE FORCING DUE TO THE WEAK WINDS. POPS ARE WARRANTED MAINLY ON ACCOUNT OF INSTABILITY...BUT THE USUAL MODEL DIFFERENCES BETWEEN THE GFS AND NAM ARE SEEN. THE NAM DEPICTS THE EASTERLY WINDS MAINTAINING A MIXED LAYER ATOP THE BOUNDARY LAYER...FROM WHICH PARCELS WILL REMAIN BUOYANT OVERNIGHT. GFS SHOWS THIS BEING LESS EFFECTIVE AND ALSO SHOWS POORER MIDLEVEL LAPSE RATES. NEVERTHELESS SLIGHT CHANCE NOCTURNAL POPS WITH SLIGHT FAVORITISM TOWARD THE BLUE RIDGE ARE APPROPRIATE. AFTERNOON CAPE IS EXPECTED TO BE GREATER SUNDAY THAN MONDAY AND SO THE HIGHEST OVERALL POPS ARE INCLUDED THEN. MAX TEMPS WILL BE A DEGREE OR TWO BELOW CLIMO SUNDAY BUT REBOUND TO ABOUT CLIMO ON MONDAY WITH AIRMASS MODIFICATION. MIN TEMPS WILL BE SLIGHTLY ABOVE CLIMO WITH NOCTURNAL CLOUD COVER. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AT 150 PM EDT FRIDAY...STARTING MONDAY NIGHT THE 500MB PATTERN HAS A SHALLOW RIDGE OVER THE SOUTHEAST STATES WITH A TROUGH AXIS OVER THE WESTERN DAKOTAS AND PROGRESSING EAST IMPINGING ON THE SE RIDGE. THE RIDGE WILL FLATTEN OUT THROUGH MID WEEK THEN THE TROUGH DIGS OVER THE SE WITH AXIS BECOMING ESTABLISHED JUST WEST OF THE APPALACHIANS BY LATE FRIDAY. RIDGE WILL BUILD AT WEEKS END OVER THE FAR WEST. AT THE SURFACE...HIGH PRESSURE WILL BE OVER THE CAROLINAS AND MID ATLANTIC TUESDAY THEN DRIFTS EAST AS COLD FRONT CROSSES THE MISS VALLEY. THIS COLD FRONT REACHES THE OHIO VALLEY BY THURSDAY AND WILL BE CROSSING OUR AREA BY FRIDAY. SCATTERED CONVECTION WILL INCREASE AS THE FRONT GETS CLOSER LATE IN THE WEEK. OVERALL...THE INSTABILITY WILL BE MODEST AT BEST. CAPE VALUES AROUND 1000 ON THE GFS FOR PIEDMONT GA AND SC LATE TUESDAY...WEAKER VALUES WED AND 700 TO 1000 THURSDAY AND FRIDAY. WIND SPEEDS IN THE LOW TO MID LEVELS NOT EXCESSIVE AS H8GHER WINDS AT THE END OF THE WEEK IN THE TROUGH. EVEN THEN THE 700MB WIND WILL BE AROUND 20 KTS WHICH IS FAIRLY LIGHT. TEMPS A LITTLE ABOVE NORMAL IN MID WEEK...DIPPING TO A LITTLE BELOW NORMAL NEXT WEEKEND WITHIN THE TROUGH. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... AT KCLT...ADJUSTED THE TEMPO TIMING TO START AT 20Z WITH A PREVIOUS AMD AS SEVERAL TSRA ARE DEVELOPING AROUND THE AIRPORT. LOW-END DOWNBURSTS EVIDENT ON TDWR SO ADDED VRB GUSTS TO THE TEMPO. CONVECTIVE INTENSITY DOES LOOK LIKE IT IS DROPPING SOMEWHAT SO WILL TAKE THE TEMPO THROUGH 23Z AND MAKE ADDITIONAL ADJUSTMENTS THEREAFTER BASED ON TRENDS. AFTER A ROUND OF STORMS MOVES THRU THE AREA...WILL KEEP ONLY CONVECTIVE DEBRIS ACROSS THE REGION OVERNIGHT...WITH A LIGHT NE WIND. THE MODEL GUIDANCE SUGGESTS BRINGING A LOW CLOUD DECK DOWN FROM THE NE IN THE EARLY MORNING HOURS. A SIMILAR EVOLUTION OCCURS IN MOST SITUATIONS LIKE THIS...WITH PLENTY OF MOISTURE...AND EASTERLY COMPONENT TO THE LOW LEVEL FLOW...WITH HIGH PRESSURE TO THE NE. THE LAMP GUIDANCE WAS GENERALLY ACCEPTED... BUT CEILINGS WERE KEPT TO MVFR ACROSS THE WRN PIEDMONT OF NC. LATER TAFS WILL HAVE TO ADDRESS THE POSSIBILITY OF IFR CEILINGS AROUND DAYBREAK...BUT FOR NOW IT IS MORE LIKELY TO STAY MVFR. ON SATURDAY...LOW CLOUD BASE WILL GRADUALLY RISE TO VFR AS BOUNDARY LAYER DEEPENS. ADDITIONAL SHOWERS OR STORMS SHOULD DEVELOP WITH HEATING AROUND MIDDAY. ELSEWHERE...SCATTERED STORMS WILL FORM FIRST ACROSS THE HIGHER TERRAIN AND THEN SLOWLY DEVELOP DOWN ACROSS THE REST OF THE FCST AREA THRU EARLY EVENING. CONFIDENCE ONLY HIGH ENUF AT KAVL/KHKY TO INCLUDE A TEMPO FOR NOW. THE UPSTATE SC TAF SITES WERE LIMITED TO VCTS/PROB30 BASED ON LACK OF COVERAGE IN CONVECTION ALLOWING MODELS. THERE COULD BE A ROUND OF SHOWERS IN THE EARLY MORNING SATURDAY AS A BACK DOOR SFC BOUNDARY MOVES DOWN FROM THE NE...BUT CONFIDENCE NOT HIGH ENUF TO MENTION. EXPECT VALLEY FOG TO FORM AT KAVL IN THE PRE- DAWN HOURS...MOST LIKELY RESTRICTING VSBY TO MVFR...UNLESS PRECIP FALLS THERE TODAY. THINK LOW CLOUD CEILING WILL REACH KHKY SATURDAY MORNING...BUT GET HUNG UP MOVING SW AS SUN STARTS TO WARM ATMOSPHERE AFTER 12Z. WIND SHOULD REMAIN N TO NE THRU THE PERIOD. MORE SHOWERS CAN BE EXPECTED WITH HEATING ON SATURDAY. OUTLOOK...A MOIST EASTERLY FLOW WILL CONTINUE THRU SUNDAY...BRINGING A GOOD CHANCE OF IFR/MVFR RESTRICTIONS SATURDAY NIGHT AND SUNDAY MORNING. LIGHT PRECIP WILL REMAIN POSSIBLE. THE THREAT FOR RESTRICTIONS WILL CONTINUE THRU SUNDAY NIGHT. DRY AIR WORKING IN FROM THE E ON MONDAY WILL BEGIN TO DIMINISH THE THREAT FOR EARLY NEXT WEEK. CONFIDENCE TABLE... 20-02Z 02-08Z 08-14Z 14-18Z KCLT HIGH 100% HIGH 100% MED 65% HIGH 85% KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAVL HIGH 100% HIGH 100% HIGH 80% HIGH 95% KHKY HIGH 100% HIGH 100% MED 66% HIGH 83% KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAND HIGH 100% HIGH 100% HIGH 83% 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 && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...DEO NEAR TERM...PM/TDP SHORT TERM...WIMBERLEY LONG TERM...DEO AVIATION...PM/TDP

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