972
FXUS62 KGSP 050002
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
802 PM EDT MON AUG 4 2025
SYNOPSIS
COLD AIR DAMMING LINGERS THROUGH AT LEAST FRIDAY BEFORE A
POTENTIAL COASTAL LOW ERODES THE WEDGE THIS WEEKEND. BELOW NORMAL
HIGH TEMPERATURES THROUGH AT LEAST SATURDAY DESPITE A GRADUAL
WARMING TREND WEDNESDAY INTO THE WEEKEND. RAIN CHANCES REMAIN, WITH
THE POTENTIAL FOR LOCALLY HEAVY RAINFALL EACH DAY.
NEAR TERM /THROUGH TUESDAY/
AS OF 610 PM: DEEPENING UPPER TROUGH OVER THE MS VALLEY WILL
ACCOMPANY HEIGHT FALLS ACROSS THE AREA THROUGH THE FORECAST
PERIOD. AS A RESULT, DEEP LAYER SOUTH TO SOUTHWESTERLY FLOW WILL
OVERRUN THE REMNANT COLD POOL/IN-SITU CAD SURFACE DOME THAT'S
CURRENTLY IN PLACE AS DEEP GULF MOISTURE FILTERS IN PWAT VALUES =>
2.00"+ ACROSS A GOOD PORTION OF THE FOOTHILLS AND PIEDMONT OVERNIGHT
TONIGHT INTO TUESDAY MORNING. ISENTROPIC LIFT WILL CONTINUE IN
THE 925-850MB LAYER, WITH LIFT BEING ENHANCED TONIGHT BY UPPER
DIVERGENCE THANKS TO THE RIGHT ENTRANCE REGION OF THE JET STREAK
DEVELOPING OVERHEAD. SOME ELEVATED CONVECTION IS POSSIBLE ALTHOUGH
THUNDER PROBABLY WILL REMAIN HIGHLY ISOLATED; CONVECTION WOULD
HOWEVER SERVE TO LOCALLY ENHANCE RAINFALL RATES. VERY SATURATED
PROFILES, DEEP WARM CLOUD DEPTHS, AND STRONG FORCING FOR ASCENT
WILL ESSENTIALLY SQUEEZE OUT MOST OF THE RAIN POTENTIAL, ESPECIALLY
ACROSS NORTHEAST GEORGIA, UPSTATE SOUTH CAROLINA AND THE FAVORABLE
UPSLOPE ZONES ALONG THE BLUE RIDGE ESCARPMENT. STEADY RAINFALL OVER
A LONG PERIOD OF TIME IS EXPECTED AND PER THE 12Z HREF ENSEMBLE
PROBABILITY MATCHED MEAN, THE AFOREMENTIONED CORRIDOR COULD PICK
UP BETWEEN 2-4" OF RAINFALL BY MID-MORNING TUESDAY, WITH A FEW
LOCATIONS EXCEEDING 4", MAINLY ALONG AND NORTH OF I-85. IN THIS
CASE, THE EXPANDED SLIGHT RISK FOR EXCESSIVE RAINFALL BY WPC IS
WARRANTED AS LOCALIZED INSTANCES OF FLASH FLOODING IS POSSIBLE. WITH
THE WEAK INSTABILITY AND RECENT RAINFALL AMOUNTS ON THE LIGHTER
SIDE, DECIDED NOT TO GO FOR A FLOOD WATCH AT THIS TIME. RECENT
CAM OUTPUT SUGGESTS AN AXIS OF HEAVIER RAINFALL MAY SET UP AWAY
FROM THE TERRAIN ACROSS THE EASTERN NC/SC PIEDMONT, POSSIBLY A
REFLECTION OF THE POSITION OF THE DEVELOPING JET STREAK. THIS
JUSTIFIES THE WPC RISKS EAST OF THE MOUNTAINS/FOOTHILLS.
AS THE DEEPER MOISTURE TRANSPORTS INTO THE CWA LATER THIS EVENING
AND INTO TONIGHT, EXPECT THE CLOUD DECK AND PRECIP TO EXPAND
ACROSS THE REST OF THE CWA AS BETTER POPS ENTER THE REGION WHEN
THE FORCING IS STRONGEST. OVERNIGHT LOWS WILL REMAIN 4-8 DEGREES
BELOW NORMAL AS THE CAD REMAINS ENTRENCHED OR EVEN REINFORCED AS
WAA INCREASES ABOVE THE COLD DOME AND A SECOND CANADIAN SURFACE
HIGH WORKS ITS WAY INTO NEW ENGLAND AND ATLANTIC CANADA. MODEL
GUIDANCE ARE KEEN ON KEEPING THE AXIS OF DEEPEST MOISTURE AND
FORCING ACROSS THE AREA ON TUESDAY AND GRADUALLY SHIFTS FROM WEST
TO EAST THROUGH TUESDAY AFTERNOON. THERE ARE SOME INSTANCES OF
A COUPLE HUNDRED J/KG OF MUCAPE, WHICH INCREASES THE THREAT FOR
LOCALIZED FLASH FLOODING IN LOCATIONS THAT RECEIVE HEAVY RAINFALL
OVERNIGHT TONIGHT. WITH THE IN-SITU CAD LOCKED IN ACROSS THE AREA
AND VERY LIKELY TO CATEGORICAL POPS IN PLACE, EXPECT AFTERNOON
HIGHS FOR TUESDAY TO RUN 15-20 DEGREES BELOW NORMAL.
SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/
KEY MESSAGES:
1) COLD AIR DAMMING REMAINS AND KEEPS HIGH TEMPERATURES BELOW NORMAL.
2) RAIN CHANCES INCREASE THROUGH THE PERIOD, ESPECIALLY FOR THE
MOUNTAINS.
AS OF 125 PM EDT MONDAY: BY TUESDAY NIGHT, THE SYNOPTIC PATTERN IS
MOSTLY UNCHANGED FROM THE PREVIOUS FORECAST. SYNOPTICALLY, TWO AREAS
OF HIGH PRESSURE TO THE WEST AND EAST OF THE AREA REMAIN RELATIVELY
LOCKED INTO PLACE, WITH WEAK TROUGHING IN BETWEEN. AT THE SURFACE, A
STOUT AREA OF HIGH PRESSURE OVER THE NORTHEAST ALSO REMAINS PARKED
AND KEEPS THE COLD AIR DAMMING IN TACT. AS THE BERMUDA HIGH
CONTINUES TO RETREAT SLIGHTLY EAST, GUIDANCE REINFORCES A STRONG
SWATH OF MOISTURE ADVECTION WHICH PERSISTS THROUGH THE PERIOD.
GUIDANCE BRINGS IN PWATS APPROACHING THE 2 INCH MARK, ESPECIALLY
EAST OF THE MOUNTAINS THROUGH THURSDAY NIGHT. FOR THIS, NBM RETAINS
CATEGORICAL POPS (75-85%) ACROSS THE MOUNTAINS AND CHANCE (40-70%)
ELSEWHERE. THIS MAY BE SLIGHTLY OVERDONE, HOWEVER, GIVEN THE
CONTINUAL MOISTURE ADVECTION, ON AND OFF SHOWERS ARE LIKELY. THIS
COULD ALSO RAMP UP ISOLATED FLASH FLOODING WHERE AREAS HAVE BEEN
RECEIVING RAINFALL THE PAST FEW DAYS. THUNDER CHANCES SHOULD REMAIN
LOWER AS THE COLD AIR DAMMING KEEPS THE AREA MORE STABLE THAN IS
TYPICAL FOR THIS TIME OF YEAR. ANY BREAKS IN THE CLOUD COVER THOUGH
COULD INCREASE INSTABILITY AND RAISE THUNDER CHANCES. AS FAR AS
TEMPERATURES, THE HIGHS LOOK TO STAY BELOW NORMAL AND WELL BELOW THE
HOT 90S THE AREA HAS HAD THIS SUMMER. DEPENDING ON HOW MUCH THE CAD
CAN WEAKEN THROUGH THURSDAY, TEMPS COULD BE IN THE UPPER 70S TO LOW
80S BY THURSDAY.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
KEY MESSAGES
1) COLD AIR DAMMING LINGERS THROUGH AT LEAST FRIDAY.
2) A POTENTIAL COASTAL LOW COULD FORM THIS WEEKEND, INCREASING RAIN
AND THUNDERSTORM CHANCES.
3) TEMPERATURES SLOWLY INCREASE BUT REMAIN BELOW NORMAL.
AS OF 135 PM EDT MONDAY: LOOKING AHEAD, THE SYNOPTIC PATTERN DOESN'T
CHANGE MUCH AS AN UPPER HIGH STARTS TO DE-AMPLIFY OUT WEST AND THE
BERMUDA HIGH RETROGRADES FURTHER WESTWARD. LONG RANGE GUIDANCE SHOWS
THE WESTERN FRINGE OF THE HIGH REMAINS MOSTLY OVER THE SOUTHEAST,
KEEPING A FAIRLY MOIST PROFILE THROUGH THE END OF THE FORECAST
PERIOD. AT THE SURFACE, THERE IS SOME UNCERTAINTY AS TO HOW THE AREA
OF HIGH PRESSURE IN THE NORTHEAST EVOLVES. AT THIS TIME, A WEAK CAD
STARTS TO ERODE TOWARD FRIDAY AS THE HIGH GETS PINCHED OFF, BUT
COULD LINGER INTO SATURDAY. EITHER WAY, THE MOSTLY STABLE AIR MASS
STICKS AROUND FOR AT THE FIRST HALF OF THE EXTENDED FORECAST. BY
SATURDAY, THERE IS SOME GUIDANCE FROM THE GFS AND EURO THAT SUGGEST
A WEAK COASTAL LOW DEVELOPING OFF THE GA/CAROLINA COAST. CONFIDENCE
REMAINS LOW TO THIS DIRECTLY AFFECTING THE CWA GIVEN THE PERSISTENT
CAD IN PLACE. HOWEVER, WILL CONTINUE TO MONITOR AS THIS AREA IS
HIGHLIGHTED BY THE NATIONAL HURRICANE CENTER WITH A 30% OF
DEVELOPMENT. REGARDLESS, HIGH PWATS NEAR OR ABOVE THE 2 INCH MARK
AND SLOWLY INCREASING INSTABILITY BY THE WEEKEND, KEEPS THE POP
CHANCES ELEVATED THROUGH THE END OF THE PERIOD. TEMPERATURES LOOK TO
SLOWLY WARM THROUGH THE EXTENDED, BUT ARE HIGHLY DEPENDENT ON THE
CAD AND WHEN IT ERODES. SO EXPECT TEMPS TO REMAIN JUST BELOW THE
NORMAL RANGE BY THE END OF THE WEEKEND.
AVIATION /00Z TUESDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: GENERALLY STEADY RAIN EXPECTED ACROSS THE
TERMINALS THIS EVENING. SOME AREAS OF MVFR OR EVEN MVFR REMAIN IN
PARTS OF THE TERMINAL AREA AT ISSUANCE TIME, BUT THINKING IS THE
RAINFALL WILL HELP REINFORCE COLD-AIR DAMMING AND PROMOTE EXPANSION
OF IFR TO LIFR CIGS OVERNIGHT. PRECIP MAY DIMINISH IN COVERAGE FOR
A TIME BUT MORE SHOWERY AND LOCALLY INTENSE RAINFALL COULD DEVELOP
IN THE EARLY MORNING; IN LIGHT OF THE ALREADY LOW CIGS NOT SURE
THIS WILL FURTHER LOWER FLIGHT CATEGORY. SOME IMPROVEMENT IN CIGS
TO MVFR APPEARS LIKELY IN SOME AREAS BY MIDDAY BUT PROB30S ARE
INCLUDED FOR CHANCE OF SHRA TO BRING CATEGORY BACK TO IFR IN THE
AFTERNOON. CAN'T RULE OUT AN ISOLATED TSRA LATE TONIGHT OR DURING
THE DAY TUE, BUT CHANCE TOO SMALL TO MENTION. WINDS MAINLY NE,
EXCEPT VERY LIGHT OR SE AT KAVL. ANOTHER EXCEPTION IS THAT KCLT
MAY EXPERIENCE PERIODS OF SW WINDS VERY EARLY IN THE PERIOD DUE
TO VARIABILITY WITH PASSING PRECIP BANDS, BUT OVERALL THEY SHOULD
RETURN TO NE LATE TONIGHT.
OUTLOOK: TEMPERATURES ONLY GRADUALLY WARM BACK UP THROUGH LATE
WEEK AS COLD-AIR DAMMING PERSISTS. FREQUENT CHANCES FOR SHRA AND
PERHAPS TSRA PRECIPITATION CHANCES CONTINUE THRU WED WITH COVERAGE
DECREASING WED NIGHT. PERIODIC RESTRICTIONS CONTINUE THROUGH LATE
WEEK, MAINLY IN THE FORM OF CIGS.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...CP
NEAR TERM...CAC/WIMBERLEY
SHORT TERM...CP
LONG TERM...CP
AVIATION...WIMBERLEY
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