449
FXUS62 KGSP 181742
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
142 PM EDT THU SEP 18 2025
SYNOPSIS
WEAK HIGH PRESSURE WILL KEEP CONDITIONS MOSTLY DRY TODAY OUTSIDE OF
A MOUNTAIN SHOWER OR STORM. AN UPTICK IN SHOWER AND STORM CHANCE ARE
POSSIBLE FRIDAY INTO THE WEEKEND, ESPECIALLY OVER THE HIGH COUNTRY.
TEMPERATURES WILL BE ON THE WARM SIDE OF NORMAL THROUGH SATURDAY
BEFORE A SLIGHT COOL DOWN COMMENCES SUNDAY INTO THE EARLY PART OF
NEXT WEEK.
NEAR TERM /THROUGH FRIDAY/
AS OF 1233 PM EDT THURSDAY: QUIET WEATHER TO CONTINUE FOR THE
NEAR TERM! MOSTLY CLEAR CONDITIONS ARE ONGOING WITH A LIGHT NE
WIND, BENEATH EXPANSIVE HIGH PRESSURE AND A NEBULOUS UPPER PATTERN.
ILL-DEFINED TROUGHINESS WILL PERSIST THROUGH MUCH OF THE PERIOD,
BUT HEIGHTS ARE GENTLY CLIMBING AHEAD OF A RIDGE AXIS EXTENDING
FROM THE OZARK PLATEAU NORTH INTO THE LOWER GREAT LAKES. AS A
RESULT, ABOVE-NORMAL HIGHS ARE EXPECTED TODAY - CLIMBING INTO
THE MID-80S ACROSS THE PIEDMONT AND UPSTATE - AND ANY CONVECTION
TRYING TO GET A FOOTHOLD IN THE MOUNTAINS WILL ENCOUNTER A MOSTLY
SUPPRESSIVE ENVIRONMENT. SO, WHILE SOME WIDELY SCATTERED SHOWERS
WILL LIKELY DEVELOP TODAY OVER THE HIGH TERRAIN...NEITHER COVERAGE
NOR INTENSITY WILL BE VERY IMPRESSIVE.
ANY CONVECTION THAT DEVELOPS WILL DISSIPATE QUICKLY AFTER SUNSET.
MOSTLY CLEAR SKIES ARE EXPECTED OVERNIGHT, EXCEPT OF COURSE IN THE
MOUNTAIN VALLEYS, WHERE ANOTHER ROUND OF VALLEY FOG AND STRATUS
SHOULD DEVELOP IN THE WEE HOURS OF FRIDAY MORNING. WIND SHOULD BE
CALM ENOUGH AND RADIATIVE COOLING EFFECTIVE ENOUGH THAT AT LEAST
PATCHY FOG MAY DEVELOP OVER PARTS OF THE NC FOOTHILLS AND SAVANNAH
RIVER VALLEY, TOO. LOWS WILL FALL INTO THE LOW 60S AGAIN.
FRIDAY WILL BE SIMILAR, WITH RIDGETOP CONVECTION IN THE AFTERNOON
BUT NO MENTIONABLE POP OUTSIDE THE MOUNTAINS. HIGHS SHOULD CLIMB
INTO THE UPPER 80S, WITH SOME FAVORED SPOTS ALONG I-77 HITTING
90 DEGREES. SKIES WILL BE MOSTLY CLEAR AGAIN, WITH SOME FAIR
WEATHER CU OUTSIDE THE MOUNTAINS.
SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/
AS OF 118 PM EDT THURSDAY: A SHORTWAVE TROUGH WILL BE IN THE
MIDST OF SHIFTING FROM THE MS VALLEY FRIDAY NIGHT AND ACROSS THE
REGION ON SATURDAY AS A CLUSTER OF DPVA BREAKS CONTAINMENT FROM A
CLOSED UPPER LOW MOVING ACROSS THE NORTHERN PLAINS. AT THE SAME
TIME, A STOUT BACKDOOR FRONT WILL APPROACH THE CWFA DURING THE
DAYTIME PERIOD SATURDAY AS A ~1030MB SURFACE HIGH SHIFTS FROM THE
ONTARIO/QUEBEC BORDER TO NEW ENGLAND, AND EVENTUALLY OFFSHORE BY
THE END OF THE PERIOD. FACTOR IN MODERATE DESTABILIZATION FOR
THIS TIME OF YEAR (750-1500 J/KG SBCAPE), PWAT VALUES BETWEEN
1.00"-1.50", AND STRONG FORCING FROM THE AFOREMENTIONED FEATURES,
SCATTERED CONVECTION SHOULD KICKOFF IN THE MOUNTAINS BY THE START
OF PEAK HEATING SATURDAY AFTERNOON. THERE ARE SOME INSTANCES OF
DRY MID-LEVEL AIR AND WEAK DEEP LAYER SHEAR, SUGGESTING THAT THIS
ACTIVITY WOULD BE OUTFLOW DRIVEN, ESPECIALLY IF INITIATION OCCURS
OUTSIDE OF THE MOUNTAINS. LATEST MODEL TRENDS ARE INCREASING POPS
FOR SATURDAY AFTERNOON AND MAKES SENSE IN THIS SCENARIO, HOWEVER,
ANY SEVERE THREAT IS VERY LOW. AFTERNOON HIGHS ARE EXPECTED TO
RUN A CATEGORY OR TWO ABOVE NORMAL. THE BACKDOOR FRONT SHOULD
SLIP SOUTH OF THE REGION SATURDAY NIGHT AND SET UP A WEDGE-LIKE
CONFIGURATION NOSING INTO THE AREA THROUGH SUNDAY WITH DRIER
NORTHEASTERLY SURFACE WINDS. LINGERING CONVECTION IS POSSIBLE
EARLY DURING THE OVERNIGHT PERIOD SATURDAY, AHEAD OF THE BACKDOOR
FRONT, BUT SHOULD DISSIPATE SOMETIME DURING THE OVERNIGHT PERIOD
AS FAVORABLE DAYTIME HEATING AND LOSS OF FORCING PRECLUDES FURTHER
DEVELOPMENT. OVERNIGHT LOWS WILL BE NEAR-NORMAL, WHILE AFTERNOON
HIGHS RETURN TO NEAR-NORMAL VALUES SUNDAY AS INFLUENCE FROM THE
SURFACE HIGH FILTERS IN SLIGHTLY COOLER AIR FROM THE NORTHEAST.
LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/
AS OF 135 PM EDT THURSDAY: SURFACE HIGH FROM THE SHORT-TERM WILL
LINGER THROUGH MONDAY BEFORE BREAKING DOWN AS THE PARENT HIGH SHIFTS
OF THE NORTH ATLANTIC AND WEAK SURFACE RIDGING REMAINS IN PLACE
GOING INTO THE EARLY PART OF NEXT WEEK. DETERMINISTIC GUIDANCE
CONTINUES TO SUPPORT THE IDEA OF DAILY DIURNAL CONVECTION ACROSS
THE MOUNTAINS EACH AFTERNOON NEXT WEEK, WHILE VERY SPARSE COVERAGE
OUTSIDE OF THE MOUNTAINS, BUT THERE ARE DIFFERENCES IN THE OVERALL
SYNOPTIC PATTERN NEXT WEEK. THE GENERAL CONSENSUS THOUGH IS THAT
THERE IS SOME TROUGH OR CLOSED LOW THAT DIGS ACROSS THE CENTRAL
CONUS AND APPROACHES THE EASTERN-THIRD OF THE COUNTRY BY THE END OF
THE FORECAST PERIOD. THIS WILL HELP TO RAMP POPS UP ACROSS THE AREA
BASED ON TIMING AND THE LOCATION OF ANY TROUGH OR CLOSED LOW THAT
DEVELOPS, WHICH DIFFERS AMONGST GUIDANCE AT THIS TIME, LEADING TO A
LOWER CONFIDENCE FORECAST. NBM SEEMS TO BE TAKING THE CLIMATOLOGICAL
APPROACH WITH TEMPERATURES NOT ESCAPING MUCH FROM THE NORMAL VALUE,
WHILE TRENDS IN POPS SHOW A SUBTLE INCREASE EACH DAY THROUGH D7.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: DRY AND VFR ACROSS THE TERMINAL FORECAST
AREA. EXPECT MOSTLY CLEAR CONDITIONS WITH SOME FEW/SCT CUMULUS
THROUGH THE AFTERNOON. SOME RIDGETOP CONVECTION WILL PROBABLY
DEVELOP...BUT REMAIN ISOLATED TO WIDELY SCATTERED...AND SO NO
MENTION IN THE 18Z TAF FOR KAVL. EXPECT LIGHT AND VARIABLE WINDS,
AND MOSTLY-CLEAR SKIES OVERNIGHT, EXCEPT FOR THE MOUNTAIN VALLEYS,
WHICH WILL SEE ANOTHER ROUND OF VALLEY FOG AND STRATUS INTO FRIDAY
MORNING. ANOTHER ROUND OF SE WINDS WILL DEVELOP AFTER DAYBREAK,
BUT SHOULD REMAIN LIGHT. BETTER COVERAGE OF SHOWERS IS EXPECTED
OVER THE MOUNTAINS FRIDAY.
OUTLOOK: ISOLATED TO WIDELY SCATTERED DIURNAL SHOWERS WILL OCCUR
AGAIN ON SATURDAY, THEN DRYING IS EXPECTED ON SUNDAY AND MONDAY.
VALLEY FOG AND STRATUS WILL BE POSSIBLE EACH MORNING WHERE CLOUDS
DO NOT INHIBIT NOCTURNAL RADIATION.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...CAC
NEAR TERM...MPR
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...MPR
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