402  
FXUS62 KGSP 240243  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
1043 PM EDT SAT SEP 23 2017  
   
SYNOPSIS
 
 
BROAD HIGH PRESSURE WILL CONTINUE TO BUILD THROUGH THE WEEKEND AND  
PERSIST THROUGH THE MIDDLE OF NEXT WEEK. IN THE MEANTIME, TROPICAL  
CYCLONES JOSE AND MARIA WILL REMAIN OFF THE EAST COAST.  
 

 
   
NEAR TERM /THROUGH SUNDAY/
 
 
AS OF 1030 PM: A COUPLE SHOWERS STILL BUBBLING UP ACROSS THE CENTRAL  
FRENCH BROAD VALLEY, BUT SHOULD DISSIPATE SHORTLY. OTHERWISE,  
PATCHES OF STRATOCU AND CIRRUS STILL OVER THE AREA, WHICH SHOULD  
GENERALLY DECREASE IN COVERAGE AS WE HEAD INTO THE OVERNIGHT HOURS.  
DEWPTS ARE FAIRLY ELEVATED, AND WINDS ARE DECOUPLING, SO I EXPECT  
PLENTY OF FOG IN THE MAJOR MOUNTAIN VALLEYS AND PATCHY FOG AROUND  
THE USUAL FOG-PRONE AREAS OF THE PIEDMONT. TEMPS WILL BOTTOM OUT A  
COUPLE CATEGORIES ABOVE NORMAL.  
 
FAIRLY BENIGN WEATHER PATTERN WILL CONTINUE THROUGH SUNDAY AS A  
LARGE EASTERN CONUS UPPER RIDGE MAKES GRADUAL EASTWARD PROGRESS  
SURFACE HIGH OVER THE NORTHEAST CONUS WITH RIDGE RUNNING DOWN THE  
SOUTHERN APPALACHIANS CHANGES LITTLE AND WILL KEEP THE AREA IN LIGHT  
NORTHEASTERLY FLOW. SLIGHT WARMING AT MID-LEVELS WILL LIMIT  
INSTABILITY, SO NO SHOWERS ARE FORECAST FOR SUNDAY.  
 
TEMPERATURES HAVE BEEN RUNNING ABOVE GUIDANCE AND MODEL BLENDS.  
CURRENT FORECAST WAS ARRIVED-AT BY ADDING A COUPLE DEGREES TO BROAD  
MODEL BLEND. THIS GIVES TEMPERATURES 5 TO 10 DEGREES ABOVE NORMAL  
TODAY AND TOMORROW.  
 
HURRICANE MARIA CONTINUES TO SPIN IN THE ATLANTIC, AND IS MOVING  
DOWN THE AXIS OF MINIMUM DEEP LAYER SHEAR TOWARDS THE NC OUTER  
BANKS. FOR UPSTATE SC AND SURROUNDING AREAS, MARIA WILL DO LITTLE  
MORE THAN SLIGHTLY ENHANCE THE NORTHEASTERLY SURFACE FLOW ON SUNDAY.  
 

 
   
SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/
 
 
AS OF 215 PM SATURDAY: DRY AND UNSEASONABLY WARM WEATHER WILL  
PERSIST THROUGH THE SHORT TERM, AS A HIGHLY AMPLIFIED UPPER RIDGE  
TIGHTENS ITS GRIP ON THE EASTERN CONUS. THE AIR MASS IS EXPECTED TO  
REMAIN DRY AND STABLE EARLY IN THE WEEK, AS A SURFACE RIDGE  
STRENGTHENS WITH THE UPPER ANTICYCLONE GRADUALLY SPILLING EAST OF  
THE NORTHERN/CENTRAL APPALACHIANS. THAT SAID, THE OFFICIAL FORECAST  
TRACK OF TROPICAL CYCLONE MARIA HAS SLOWLY EDGED WESTWARD THROUGH  
TIME. WHILE THERE IS GOOD AGREEMENT THAT THIS INCREASES THE PRESSURE  
GRADIENT BETWEEN MARIA AND THE SURFACE RIDGE, POSSIBLY LEADING TO  
BREEZY CONDITIONS BY TUESDAY, THERE IS DISAGREEMENT ON WHETHER LOW  
LEVEL MOISTURE INCREASES IN THIS FLOW. IF THE MOISTURE DOES INCREASE,  
THEN THE ATMOSPHERE COULD BECOME UNSTABLE ENOUGH FOR ISOLATED  
CONVECTION OVER THE AREA. FOR NOW, HAVE KEPT THE FORECAST DRY DUE TO  
THE UNCERTAINTY. ALSO UNCERTAIN IS THE AMOUNT OF ANY HIGH CLOUDS  
THAT WOULD MOVE IN FROM THE EAST AROUND THE PERIPHERY OF THE  
CYCLONE. AGAIN, DUE TO THE UNCERTAINTY, DID NOT LOWER THE HIGHS AS  
MUCH AS A MODEL BLEND WOULD SUGGEST, BUT DID DROP THEM A DEGREE OR  
SO ACROSS THE I-77 CORRIDOR. FOR NOW, THIS KEEPS HIGHS AND LOWS 5 TO  
10 DEGREES ABOVE NORMAL.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
 
 
AS OF 205 PM EDT SATURDAY: THE EXTENDED FCST PICKS UP AT 00Z ON  
WEDNESDAY WITH THE PERSISTENT UPPER RIDGE BEGINNING TO WEAKEN AS  
A NORTHERN STREAM UPPER TROF MOVES UP AND OVER THE RIDGE FROM THE  
WEST. AS WE MOVE INTO THURS AND FRI, THE UPPER TROF AXIS WILL  
BROADEN AND AMPLIFY OVER THE GREAT LAKES AND IS EXPECTED TO DIG  
FARTHER SOUTHWARD AND APPROACH THE FCST AREA BY THE END OF THE  
PERIOD ON SAT. AT THE SFC, HIGH PRESSURE WILL STILL BE LINGERING  
OVER THE REGION ON WED AS TC MARIA REMAINS JUST OFF THE CAROLINA  
COAST. COMPARED TO PREVIOUS FCSTS, THE TREND HAS BEEN TO BRING  
MARIA A BIT CLOSER TO THE COAST ON WED, AND THEN MOVE HER FARTHER  
OFFSHORE LATER ON THURS. THIS NEWER SCENARIO WILL LIKELY RESULT IN  
A LESS IMPRESSIVE OVERALL FROPA ON THURS. IN THE WAKE OF THE FRONT,  
COOLER HIGH PRESSURE WILL OVERSPREAD THE REGION ON FRI AND LINGER  
WELL INTO THE WEEKEND. AS FOR THE SENSIBLE WX, MOSTLY DRY CONDITIONS  
ARE STILL ANTICIPATED, ALTHOUGH THE LONG-RANGE MODELS ARE SHOWING  
MORE MOIST NLY FLOW ON WED AS MARIA GETS CLOSER TO THE CAROLINA  
COAST. TEMPS WILL REMAIN WELL ABOVE CLIMATOLOGY THRU THURS AND  
COOL TO BELOW NORMAL BY SAT.  
 

 
   
AVIATION /03Z SUNDAY THROUGH THURSDAY/
 
 
AT KCLT AND ELSEWHERE: NOT MUCH CHANGE FOR THE 00Z TAFS. A FEW  
SHOWERS LINGERING NORTH OF KAVL FOR FIRST HOUR OR SO OF TAF PERIOD,  
BUT OTHERWISE SHOULD BE QUIET. CU FIELD WILL DISSIPATE, THEN  
MOUNTAIN VALLEY FOG WILL DEVELOP OVERNIGHT AS IT HAS THE LAST FEW  
NIGHTS. AN UPPER RIDGE WILL PERSIST JUST NORTH OF THE AREA, KEEPING  
A STEADY AND LIGHT NORTHEASTERLY FLOW ATOP THE AREA THE PERIOD. THE  
AIR MASS WILL BE MORE STABLE TOMORROW, SO ONLY A FAIR WX CU FIELD  
UNDER AREAS OF CIRRUS EXPECTED. WINDS STAY OUT OF THE NE TOMORROW.  
 
OUTLOOK: DRY CONDITIONS EXPECTED FOR THE FIRST HALF OF THE WEEK.  
UNDER MOSTLY CLEAR SKIES AND CALM CONDITIONS, FOG AND/OR LOW STRATUS  
ARE LIKELY IN THE MTN VALLEYS EACH OF THE NEXT FEW MORNINGS.  
 
CONFIDENCE TABLE...  
 
02-08Z 08-14Z 14-20Z 20-00Z  
KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KAVL HIGH 95% LOW 44% HIGH 100% HIGH 100%  
KHKY HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KAND HIGH 100% HIGH 100% 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:  
 
WWW.WEATHER.GOV/GSP/AVIATION  
 

 
   
GSP WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
NC...NONE.  
SC...NONE.  
 

 
 

 
SYNOPSIS...JPT  
NEAR TERM...ARK/WJM  
SHORT TERM...RWH  
LONG TERM...JPT  
AVIATION...ARK  
 
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