186
FXUS62 KGSP 171053
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
653 AM EDT THU SEP 17 2026
WHAT HAS CHANGED
NO SIGNIFICANT CHANGES TO THE FORECAST.
THE AVIATION DISCUSSION WAS UPDATED TO REFLECT THE RECENT 12Z TAF
ISSUANCE.
KEY MESSAGES
1. SUMMER-LIKE WEATHER WITH HOT CONDITIONS AND AFTERNOON SHOWERS
AND THUNDERSTORMS CONTINUE THROUGH MONDAY. PRECIPITATION CHANCES
CONTINUE TUESDAY AND WEDNESDAY WITH TEMPERATURES DROPPING TO NEAR
OR EVEN BELOW NORMAL.
DISCUSSION
KEY MESSAGE 1: SUMMER-LIKE WEATHER WITH HOT CONDITIONS AND AFTERNOON
SHOWERS AND THUNDERSTORMS CONTINUE THROUGH MONDAY. PRECIPITATION
CHANCES CONTINUE TUESDAY AND WEDNESDAY WITH TEMPERATURES DROPPING
TO NEAR OR EVEN BELOW NORMAL.
ANOMALOUSLY DEEP 500MB RIDGE REMAINS IN PLACE OVER THE SOUTHEASTERN
QUADRANT OF THE CONUS; A QUASI-STATIONARY FRONT REMAINS ON THE
NORTHERN PERIPHERY OF THIS RIDGE, ACROSS THE SOUTHERN GREAT
LAKES. ON THURSDAY THE RIDGE WILL BEGIN TO RETROGRADE, AS A
SHORTWAVE PASSES ITS AXIS, WHICH INDUCES HEIGHT FALLS ACROSS THE
NORTHEAST, TURNS LOW-LEVEL FLOW MORE NORTHWESTERLY AND STARTS TO
BRING THE FRONTAL ZONE SOUTHWARD IN OUR DIRECTION. PWATS INCREASE,
AND SEEMINGLY THROUGH AIRMASS MODIFICATION TEMPERATURES TREND
WARMER. MOST CAMS DEPICT AT LEAST ISOLATED SHOWERS/STORMS DEVELOPING
OVER THE MOUNTAINS/FOOTHILLS THURSDAY AFTERNOON, IN PART DUE TO
THE CWA BECOMING EXPOSED TO WEAK VORT RIPPLES ROUNDING THE RIDGE,
BUT OTHERWISE JUST WITH VERTICAL PROFILES BECOMING MORE FAVORABLE
FOR RIDGETOP CONVECTION.
THE ACTUAL COLD FRONT REMAINS TO OUR NORTH THURSDAY BUT MAY REACH
THE NW FRINGE OF THE AREA FRIDAY, CONTINUING TO OOZE SOUTHEASTWARD
FRIDAY NIGHT, BECOMING ZONAL IN ORIENTATION AS A COOLER SURFACE
HIGH BUILDS INTO THE NORTHEAST STATES. SOME DEGREE OF EASTERLY FLOW
IS SHOWN TO DEVELOP IN LOW LEVELS NEAR THE FRONT, PARTICULARLY
OVER NC, INTRODUCING BETTER LOW-LEVEL MOISTURE. POPS ACCORDINGLY
INCREASE FURTHER WITH LIKELY VALUES FORECAST ALONG THE BLUE RIDGE
ESCARPMENT AND MOUNTAIN RANGES BETWEEN IT AND THE TN BORDER. TEMPS
TREND STILL WARMER WITH FRIDAY LIKELY BEING THE WARMEST DAY OF THE
PERIOD, WITH UPPER 80S FOR THE MTN VALLEYS AND LOWER 90S FOR MOST
OF THE PIEDMONT.
MEANWHILE, A COMPACT UPPER LOW WILL ADVECT WESTWARD FROM THE
ATLANTIC, CENTERING OVER FLORIDA BY FRIDAY. BY SATURDAY THE
SHORTWAVE WHICH WILL HAVE HELPED DRIVE THE FRONTAL ZONE INTO THE
AREA WILL BE MOVING OFF PAST NEWFOUNDLAND, SO THE FRONT SHOULD STALL
OVER THE CAROLINAS/GEORGIA, OR POSSIBLY WASH OUT. THE FRONT WILL
REMAIN BETTER DEFINED IN THE CORN BELT REGION, THOUGH INITIALLY
STILL STATIONARY. THE PATTERN OVER OUR AREA BECOMES A BIT MURKY
ALOFT; VERY WEAK UPSLOPE FLOW AND/OR CONVERGENCE MAY BE FACTORS
AT 850 MB, AS THE UPPER LOW (OR VERY WEAK SFC REFLECTION) DRIFTS
WESTWARD INTO THE GULF. NEARER THE SURFACE, EASTERLY FLOW SHOULD
CONTINUE ALONG THE FRONT OR ITS REMNANT. THUS SOME RELATIVELY HIGH
POPS (30-60% PIEDMONT, 70-80% OVER THE MOUNTAINS) ARE JUSTIFIED
SATURDAY, WITH A SLOW DECLINE SATURDAY NIGHT. POPS ARE LOWER OVERALL
SUNDAY AS WINDS WEAKEN AND BECOME MORE CHAOTIC AT 850 MB REDUCING
THE LIFT AT THAT LEVEL; HOWEVER, NEAR-SFC FLOW TURNS SOUTHERLY AGAIN
SO ABOVE-CLIMO POPS CONTINUE OVER THE ESCARPMENT. TEMPERATURES TREND
LOWER BUT STILL ABOVE NORMAL FOR THOSE DAYS. THOUGH WE ARE NOT IN
ANY WPC ERO RISK AREAS THROUGH DAY 5, IT WOULD APPEAR SLOW-MOVING
SHOWERS OR STORMS PRODUCING LOCALLY HEAVY RAINFALL CAN'T BE RULED
OUT FRI-SUN, ON ACCOUNT OF THE WEAK STEERING FLOW ALOFT.
ON SUNDAY MOST GUIDANCE DEPICTS ANOTHER SHORTWAVE ADVANCING THROUGH
THE GREAT LAKES, PICKING UP THE FRONT AND DRIVING IT SOUTH AS A COLD
FRONT AGAIN, SUGGESTING AN UPTICK IN POPS MONDAY AND TUESDAY AS
THE FRONT MAKES GRADUAL PROGRESS INTO THE AREA. WITH THE SFC HIGH
BEHIND THE FRONT BEING STRONGER, BEING SUPPORTED TO SOME DEGREE
BY CONFLUENT UPPER FLOW, THIS EVOLUTION HAS A DECENT CHANCE OF
DRIVING COOLER AIR DOWN THE EAST COAST TUE AND ESPECIALLY WED IN
A FASHION SIMILAR TO CAD (A "LOOKALIKE" EVENT). THERE IS A DECENT
SIGNAL FROM GUIDANCE FOR TEMPS TO FALL BACK TO NEAR NORMAL TUESDAY,
THOUGH THERE IS SPREAD IN HOW FAR THE SURFACE FRONT REACHES BEFORE
STALLING/REVERSING, SO DISAGREEMENT ON HOW LONG THE COOLER AIR
REMAINS WITH US (AND THUS ON TEMPS WED). THE 16/12Z ECMWF, MOST OF
ITS ENSEMBLE MEMBERS AS WELL AS A HANDFUL OF MEMBERS OF THE 16/18Z
GFS ENSEMBLE, DEVELOP AN UPPER LOW IN THE MIDWEST WHICH IMPEDES
THE PROGRESS OF THE FRONT AND SUGGESTS WARMER AND WETTER CONDITIONS
MIDWEEK, COMPARED TO THE RELATIVELY DRIER GFS AND SIMILAR MEMBERS
OF THE MAJOR ENSEMBLES. THE 17/00Z OPERATIONAL GFS APPEARS TO HAVE
TRENDED MORE LIKE THE 16/12Z ECMWF RUN, SO CONFIDENCE REMAINS LOW
AT THAT TIME.
AVIATION /12Z THURSDAY THROUGH MONDAY/
AT KCLT AND ELSEWHERE: MOSTLY VFR CONDITIONS WILL PREVAIL THROUGH
THE TAF PERIOD OUTSIDE OF MORNING MOUNTAIN VALLEY FOG AND LOW
STRATUS. KEPT THE TEMPO IN FOR KAVL FOR 3SM VSBY AND OVC002 CIG
THROUGH 13Z. CAN'T RULE OUT FOG DEVELOPING ELSEWHERE, ESPECIALLY AT
TERMINALS NEAR BODIES OF WATER. IN THIS CASE, PUT A TEMPO FOR 1/4SM
VSBY AND OVC001 CIG FOR THE FOG AND LOW STRATUS POTENTIAL AT KHKY AS
WELL. ANY FOG OR LOW STRATUS THAT DEVELOPS SHOULD QUICKLY DISSIPATE
SHORTLY AFTER SUNRISE. MOSTLY DRY CONDITIONS WITH AFTERNOON VFR CU,
BUT ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON,
WITH BETTER COVERAGE CLOSER TO THE NC TERMINALS. CONFIDENCE IS ONLY
HIGH ENOUGH TO MAINTAIN A VCSH MENTION AT KAVL, WHILE KEEPING THE
REST OF THE TAF SITES DRY. LIGHT AND VARIABLE WINDS OVERNIGHT WILL
PICK UP OUT SOUTH TO SOUTHEAST WINDS THROUGH THE DAY TIME PERIOD AT
3-6 KTS, WHILE KAVL MAINTAINS A NORTH-NORTHWEST COMPONENT. MID/HIGH
CLOUDS ARE LIKELY TO MOVE IN DURING THE EVENING. ANOTHER ROUND OF
MOUNTAIN VALLEY FOG AND LOW STRATUS IS POSSIBLE BEFORE DAYBREAK
FRIDAY.
OUTLOOK: INCREASED SHOWER AND THUNDERSTORM CHANCES WITH ASSOCIATED
RESTRICTIONS THROUGH MONDAY. MOUNTAIN VALLEY FOG AND LOW STRATUS
WILL BE POSSIBLE EACH MORNING.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
CAC/JCW
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