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Local forecast by
"City, St"
  
000
FXUS62 KGSP 201839
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
239 PM EDT SAT SEP 20 2014

.SYNOPSIS...
A WEAK RIDGE OF HIGH PRESSURE WILL LINGER ATOP THE REGION THROUGH  
TONIGHT. TEMPERATURES WILL WARM ON SUNDAY BEFORE A COLD FRONT 
CROSSES THE CAROLINAS LATER THAT NIGHT. COOL AND DRY HIGH PRESSURE 
WILL THEN SPREAD ACROSS THE REGION AND REMAIN IN PLACE THROUGH AT 
LEAST MID WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 235 PM...DESPITE MDL OUTPUT SHOWING MTN CONVECTION...ATMOS 
SHUD REMAIN CAPPED THIS AFTERNOON AND EVENING WITH ONLY RIDGE TOP CU 
DEVELOPING. THERE WILL ALSO BE SOME JET STREAM CIRRUS ASSOCIATED 
WITH THE LOW PRESSURE SYSTEM MOVING UP THE SERN COAST. GUIDANCE 
SUGGESTS A GOOD NITE FOR AT LEAST PATCHY DENSE MTN VALLEY FOG... 
WHILE MOST AREAS OUTSIDE OF THE MTNS GENERALLY TOO DRY. SKIES SHOULD 
BE MOSTLY CLEAR WITH LOWS NEAR TO SLIGHTLY BELOW NORMAL.

AN UPPER TROF DIGS TOWARD THE AREA SUNDAY PUSHING A FRONT INTO THE 
MTNS BY THE END OF THE PERIOD. LITTLE IN THE WAY OF PRECIP IS 
EXPECTED UNTIL VERY LATE IN THE PERIOD...THEN ONLY ACROSS THE MTNS 
WHERE MOISTURE...FORCING AND INSTABILITY WILL BE BETTER. LOW LEVEL 
FLOW REMAINS WLY KEEPING AREAS OUTSIDE OF THE MTNS DRIER WITH A LOW 
LEVEL WARM NOSE KEEPING THE ATMOS GENERALLY CAPPED WITH ONLY WEAK 
ELEVATED INSTABILITY AT BEST. BRING CHC POP INTO THE TN BORDER 
COUNTIES BY LATE AFTERNOON...WITH SLIGHT CHC ACROSS THE REST OF THE 
MTNS...AND A DRY FCST ELSEWHERE. CANNOT RULE OUT AN ISOLATED SEVERE 
WIND GUST ACROSS THE MTNS GIVEN THE INCREASING SHEAR AND DRY MID 
LEVELS...BUT CHC IS LOW. HIGHS WILL BE 5 TO 10 DEGREES ABOVE NORMAL 
AS THICKNESSES INCREASE SIGNIFICANTLY AHEAD OF THE FRONT ALONG WITH 
THE INCREASING WLY LOW LEVEL FLOW.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 145 PM EDT SATURDAY...THE SHORT TERM FORECAST PERIOD 
INITIALIZES SUNDAY EVENING AMIDST AN UPPER TROF EJECTING TO THE EAST 
ACROSS THE GREAT LAKES REGION WITH A WEAK SURFACE LOW SLIDING 
THROUGH SOUTHERN ONTARIO.  A COLD FRONT WILL BE DRAPED FROM THIS 
PARENT SURFACE LOW SOUTHWEST ALONG THE APPALACHIAN MOUNTAINS.   
CLOSER TO HOME...A WEAK UPPER/SURFACE LOW OFF THE CAROLINA COASTLINE 
WILL MIGRATE NORTHWARD WITH NO SIGNIFICANT IMPACTS EXPECTED.  THERE 
REMAINS SOME UNCERTAINTY REGARDING THE AMOUNT OF ONGOING CONVECTION 
AT FORECAST INITIALIZATION.  THE USUALLY MORE AGGRESSIVE/UNSTABLE 
NAM INDICATES NEARLY 1000J/KG SBCAPE ACROSS THE WARM SECTOR WITH 
CONVECTION SPREAD OUT ACROSS THE HIGH TERRAIN AND NC 
PIEDMONT...LIKELY TIED TO THE PREFRONTAL SURFACE TROF AS A FOCUSING 
MECHANISM.  THE GFS/ECMWF FAVOR A MORE STABLE SOLUTION WITH LITTLE 
TO NO PREFRONTAL TROF FOCUSED ACTIVITY.  ALTHOUGH SHEAR WILL BE 
INCREASING...THE BEST UPPER JET DYNAMICS WILL PASS BY TO THE 
NORTH...THEREFORE DECIDED TO LEAN TOWARD THE MORE SUBTLE SOLUTIONS 
OF THE GFS/ECMWF.  THE FRONT WILL SWEEP THROUGH THE REGION DURING 
THE OVERNIGHT HOURS WITH OVERALL CONVECTIVE COVERAGE EXPECTED TO 
DISSIPATE WITH LOSS OF HEATING.  THE FRONT LOOKS TO CLEAR THE 
FORECAST AREA BY NLT NOON ON MONDAY BEFORE ANY DIURNAL HEATING 
INDUCED INSTABILITY CAN PLAY A FACTOR. 

BEHIND THE FRONT ON MONDAY AFTERNOON...UPPER TROF AXIS AND 
ASSOCIATED VORTICITY MAXIMA WILL SLIDE THROUGH THE SOUTHERN/CENTRAL 
APPS.  MODERATE TO STRONG NORTHWEST FLOW THROUGH THE PROFILE WILL 
LEAD TO THE POSSIBILITY OF A FEW UPSLOPE INDUCED SHOWERS ALONG THE 
SPINE OF THE APPS.  THUS THE FORECAST WILL FEATURE CHANCE LEVEL POPS 
ACROSS THE HIGH TERRAIN SUNDAY NIGHT TAPERING TO SLIGHT CHANCE POPS 
ACROSS THE REMAINDER OF THE FORECAST AREA THROUGH MONDAY MORNING TO 
ACCOUNT FOR PASSAGE OF THE FRONT AND WEAK NORTHWEST UPSLOPE FLOW 
SHOWERS ALONG THE TN LINE.  THE ABOVE MENTIONED UPPER FEATURES WILL 
SLIDE EAST LATE IN THE DAY MAKING WAY FOR RISING HEIGHTS AND 
CANADIAN HIGH PRESSURE AT THE SURFACE THAT WILL LAST THROUGH THE 
PERIOD.  THIS WILL YIELD MORE FALL LIKE CONDITIONS WITH TEMPERATURES 
GENERALLY 8-10 DEGREES BELOW NORMAL AMONGST DRIER NORTHERLY FLOW.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 2 PM SATURDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON 
WEDNESDAY WITH HEIGHTS STEADILY RISING AS A BROAD AND STEEP UPPER 
RIDGE SPREADS ACROSS THE REGION. THIS IMPRESSIVE RIDGE IS EXPECTED 
TO REMAIN IN PLACE THRU NEW DAY 7 OVER THE EASTERN HALF OF THE CONUS 
WHILE ANOTHER STEEP UPPER TROF DIGS DOWN OVER THE WEST COAST BY 
THE END OF THE MEDIUM RANGE. 

AT THE SFC...STRONG CANADIAN HIGH PRESSURE WILL BE CENTERED TO OUR 
NORTH WITH COOL AND DRY AIR OVER THE FCST AREA. OVER THE NEXT COUPLE 
OF DAYS...THE LONG RANGE GUIDANCE SUGGESTS THAT THIS HIGH WILL 
GRADUALLY DRIFT EASTWARD WITH SOME DEEPER LYR MOISTURE ENCROACHING 
UPON THE CWFA FROM THE SOUTH AND EAST. THE MODELS DIFFER WITH 
REGARDS TO HOW FAR NW THIS DEEPER MOISTURE WILL EXPAND. THE ECMWF 
CONTINUES TO SHOW GREATER COVERAGE OVER THE CWFA ON FRI AND MOST OF 
SAT WHILE THE NEWER RUN OF THE GFS KEEPS THE MOISTURE PLUME MORE TO 
THE SOUTH ON FRI AND THEN EXPANDS IT FARTHER NORTH ON SAT. 
INTERESTINGLY...THE LATEST 12Z RUN OF THE CMC MODEL KEEPS THE DEEPER 
MOISTURE EVEN FARTHER SOUTH THAN THE GFS THRU ITS FCST ENDING TIME 
OF 12Z FRI. BASED ON THE MIXED MODEL SPREAD TOWARDS THE END OF THE 
FCST PERIOD...I DID NOT MAKE ANY MAJOR CHANGES TO THE SENSIBLE FCST. 
I GRADUALLY INCREASED POPS TO SLIGHT CHANCE DURING THE LATTER PART 
OF THURS AND KEEP THEM THERE FOR FRI. I DID INCLUDE AN AREA OF SOLID 
CHANCE VALUES OVER THE FAR SOUTHERN ZONES FOR SAT AFTERNOON INTO SAT 
EVENING...OTHERWISE MOST OTHER AREAS STILL ONLY CARRY SLIGHT CHANCE. 
TEMPS WERE CHANGED LITTLE WITH VALUES REMAINING A FEW DEGREES BELOW 
CLIMATOLOGY FOR LATE SEPT.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ALL BUT KAVL...VFR. FEW CONVECTIVE CU WITH JET STREAM 
CIRRUS THIS AFTERNOON. CU DIMINISHES THIS EVENING BUT CIRRUS 
REMAINS. CONVECTIVE CU RETURNS WITH HEATING SUNDAY. NELY WIND 
BECOMES LIGHT NLY OVERNIGHT THEN INCREASES FROM THE WNW WITH MIXING 
SUNDAY.

KAVL...RIDGE TOP CU THIS AFTERNOON DISSIPATES THIS EVENING LEAVING 
SOME CIRRUS IN PLACE. ALL PARAMETERS SHOW A GOOD NIGHT FOR VALLEY 
FOG. HAVE GONE LIFR AROUND DAYBREAK TO INDICATE THIS...BUT VLIFR 
QUITE POSSIBLE. FOG SHUD BURN OFF QUICKLY AFTER DAYBREAK WITH CU 
DEVELOPING AGAIN WITH HEATING. SLY WIND THIS AFTERNOON BECOMES CALM 
OVERNIGHT THEN PICKS UP FROM THE NORTH WITH MIXING SUNDAY.

OUTLOOK..A COLD FRONT WILL BRING A CHANCE FOR RESTRICTIONS MAINLY 
OVER THE MTNS SUNDAY NIGHT AND MONDAY MORNING. HIGH PRESSURE BUILDS 
BACK IN EARLY NEXT WEEK.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z 
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%     
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%     
KAVL       HIGH 100%     HIGH 100%     MED   71%     HIGH  87%     
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: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

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

&&

$$
SYNOPSIS...JPT
NEAR TERM...RWH
SHORT TERM...CDG
LONG TERM...JPT
AVIATION...RWH





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Page last modified: January 20, 2010

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