761  
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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