929
FXUS62 KGSP 060740
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
340 AM EDT TUE MAY 6 2025
SYNOPSIS
MOSTLY DRY WEATHER IS EXPECTED TODAY WITH TEMPERATURES SLIGHTLY
BELOW NORMAL FOR EARLY MAY. ANOTHER UNSETTLED PATTERN WILL LIKELY
DEVELOP FOR THE SECOND HALF OF THE WEEK, WITH CHANCES FOR RAIN AT
TIMES WEDNESDAY THROUGH THE WEEKEND.
NEAR TERM /THROUGH TONIGHT/
AS OF 245 AM TUE: SWIRL AT CENTER OF UPPER LOW IS SEEN ON WATER
VAPOR IMAGERY NEAR CINCINNATI AT THIS HOUR. THE LOW WILL WOBBLE ITS
WAY TOWARD NEW ENGLAND OVER THE NEXT 24 HRS. WEAK WARM ADVECTION
WILL OCCUR OVER EAST TN AND THE NC MOUNTAINS THIS MORNING IN THE
WAKE OF THE LOW, WITH AN ASSOCIATED LAYER OF SHALLOW MOISTURE
RESPONSIBLE FOR SOME CLOUD COVER IN OUR WESTERN CWA. SOME MOUNTAIN
VALLEY FOG WILL DEVELOP, AS LONG AS THE CLOUDS REMAIN PATCHY AS
EXPECTED. SKIES SHOULD TREND CLEARER FOR A TIME AFTER DAYBREAK. A
DRY SFC HIGH AND UPPER RIDGE WILL EXPAND INTO THE AREA TODAY AS
THE LOW DEPARTS. A SHALLOW/SPOTTY CU FIELD LOOKS TO DEVELOP UNDER
THE SUBSIDENCE INVERSION. POPS REMAIN IN THE SINGLE DIGITS AND
THUS NO PRECIP MENTION IS MADE IN THE FCST. TEMPS WILL RISE BACK
CLOSER TO NORMAL THIS AFTERNOON BUT STILL WITH LOW HUMIDITY.
TONIGHT, UPSTREAM OF THE RIDGE OVER THE LOWER MS VALLEY, BROADLY
DIVERGENT UPPER FLOW AND SLIGHT PROGRESSION OF THE BLOCKING
PATTERN WILL LEAD TO MOIST UPGLIDE NORTH OF A WARM FRONT AS WELL
AS A DEEP LAYER OF UPWARD MOTION. THIS WILL MOISTEN THE COLUMN
FROM THE TOP DOWN OVERNIGHT AND BRING HIGH ALTITUDE CLOUD COVER
OVER THE CWA FROM THE SOUTHWEST, BEGINNING AROUND MIDNIGHT IF NOT
A LITTLE SOONER. MODELS ARE SPLIT AS TO HOW QUICKLY THE UPGLIDE
OVERCOMES THE DRY AIR IN PLACE IN LOW LEVELS, BUT WITH ONLY VERY
SPOTTY QPF RESPONSE ASIDE FROM THE GFS, POPS ARE BEING KEPT BELOW
SLIGHT CHANCE UNTIL AFTER 12Z WED. MIN TEMPS WILL REMAIN NEAR
NORMAL IN THE SOUTHWEST WHERE CLOUD COVER WILL BE A FACTOR, BUT
WITH THE RELATIVELY DRY DEWPOINTS, LIGHT WINDS, AND LATER ARRIVAL
OF CLOUDS, MOUNTAIN VALLEYS AND THE NORTHERN TIERS OF NC COUNTIES
WILL SEE MINS A LITTLE BELOW NORMAL.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
AS OF 316 AM EDT TUESDAY...
KEY MESSAGES:
1) INCREASING RAIN CHANCES ON WEDNESDAY, BUT LITTLE CHANCE OF
THUNDER.
2) BELOW-NORMAL TEMPERATURES ON WEDNESDAY THANKS TO DEVELOPING IN
SITU COLD-AIR DAMMING.
3) THUNDERSTORMS ARE POSSIBLE THURSDAY, BUT MAY OCCUR MORE IN
THE EVENING AND EARLY OVERNIGHT HOURS RATHER THAN THE TYPICAL
AFTERNOON PEAK.
ON WEDNESDAY, THE UPPER LOW OVER NEW ENGLAND WILL LIFT NORTHEASTWARD
ALONG THE ATLANTIC COAST INTO NOVA SCOTIA, WHILE THE SECOND LOW
OVER THE OZARKS SLOWLY OPENS BACK UP INTO THE MEAN FLOW. A SPURT
OF DPVA WILL DEVELOP DURING THE DAYTIME HOURS IN THE RESULTING
ELONGATED BUT ALMOST ZONALLY-ORIENTED TROUGH...WHILE AT THE SURFACE,
HIGH PRESSURE WILL BE MAINTAINED OVER THE MID-ATLANTIC AND INTO
THE CAROLINAS. WHAT APPEARS TO BE A WEAK QUASI-STATIONARY FRONT
OVER THE DEEP SOUTH WILL BE ACTIVATED BY THE DEVELOPING LOBE
OF VORTICITY...RESULTING IN WHAT COULD BEST BE DESCRIBED AS AN
OPEN WAVE ALONG THAT BOUNDARY. ALTHOUGH A HANDFUL OF ENSEMBLES
DO MANAGE TO BRING THAT BOUNDARY BACK ACROSS OUR AREA AS A WARM
FRONT, THE MAJORITY OF GUIDANCE KEEPS PROFILES COMPLETELY STABLE
AND WEDGE-LIKE...WITH NO INSTABILITY TO SPEAK OF, ONLY GENTLE
ISENTROPIC UPGLIDE ACROSS THE AREA. THIS'LL RESULT IN INCREASING
RAIN CHANCES THROUGHOUT THE DAY WEDNESDAY, AS PROFILES MOISTEN FROM
THE TOP DOWN...BUT MINIMAL THUNDER CHANCES. ALL TOLD, THIS LOOKS
LIKE A WEAK IN SITU COLD-AIR DAMMING EVENT, AND THAT DIABATIC
COOLING SHOULD RESULT IN TEMPS A CATEGORY OR TWO BELOW-NORMAL
WEDNESDAY AFTERNOON, ESPECIALLY ACROSS THE WESTERN TWO-THIRD OF
THE FORECAST AREA, WHERE RAIN AND CLOUDS WILL ARRIVE FIRST.
BY WEDNESDAY NIGHT AND EARLY THURSDAY, THE UPPER PATTERN SHOULD
BEGIN TO AMPIFY; WHAT'S LEFT OF THE NOW-TROUGH OVER THE OZARKS WILL
PHASE WITH A SECOND Z500 WAVE DIPPING DOWN OFF THE GREAT LAKES.
THIS WILL PRODUCE A RESURGENCE IN DEEP SYNOPTIC FORCING ON THURSDAY,
BUT THE LATEST OPERATIONAL GUIDANCE DEPICTS IT ARRIVING PAST
PEAK HEATING ON THURSDAY...AND MORE TOWARD THE EVENING/OVERNIGHT
TIMEFRAME. NONETHELESS, THERE ARE AT LEAST MODEST HEIGHT FALLS
DEPICTED THROUGH THE DAY ON THURSDAY, SO THERE'S AT LEAST SOME
IMPROVEMENT IN MID-LEVEL LAPSE RATES, AND PRETTY GOOD AGREEMENT
THAT WE'LL BE ABLE TO MIX OUT THE WEDGE AND DEVELOP SOMEWHERE
ON THE ORDER OF 800-1200 J/KG SBCAPE. INCREASINGLY CONSTRAINED
MID-LEVEL FLOW WILL RESULT IN SOMETHING AKIN TO A SPEED MAX,
OR AT LEAST A CORRIDOR OF STRONGER FLOW OVER THE CAROLINAS,
AND SO ALTHOUGH THE LOW-LEVEL KINEMATICS LOOK POOR, BORDERING ON
NONEXISTENT, THE DEEP LAYER SHEAR COULD ATTAIN VALUES OF 30+ KTS.
IT'LL BE UNIDIRECTIONAL...BUT COULD PROVIDE SOME ORGANIZATION FOR
ANY CONVECTION THAT DEVELOPS LATE THURSDAY. IN PARTICULAR, THE
OPERATIONAL MODELS ALL SHOW SOME FAINT, BUT UNMISTAKABLE REINFORCING
FRONT SLIDING ACROSS THE AREA LATE THURSDAY EVENING...OR AT LEAST
A WEAK LOW-LEVEL CONVERGENCE ZONE...WHICH COULD PROVIDE THE FOCUS
FOR SUCH CONVECTION TO DEVELOP OVERNIGHT INTO FRIDAY.
LONG TERM /FRIDAY THROUGH MONDAY/
AS OF 331 AM EDT TUESDAY...
KEY MESSAGES:
1) UNCERTAINTY REMAINS FOR FRIDAY NIGHT AND SATURDAY, WITH RAIN
POSSIBLE, BUT AMOUNTS AND TIMING UNCLEAR.
2) BETTER CONFIDENCE ON RAIN ASSOCIATED WITH HYBRID COLD-AIR
DAMMING ON SUNDAY AND MONDAY.
AS A WEAK REINFORCING COLD FRONT SLIDES EAST OF THE AREA ON FRIDAY,
GUIDANCE DEPICTS RAPID CYCLOGENESIS OVER THE MID-ATLANTIC AS
THE NORTHERN PORTION OF THAT BOUNDARY INTERACTS WITH A DEEPENING
UPPER LOW. BY THE END OF THE DAY, WE'LL BE SET UP FOR WHAT ALMOST
LOOKS LIKE A...DISPLACED REX BLOCK...WITH AN UPPER LOW CHURNING
OVER THE DEEP SOUTH / GULF COAST REGION, AND RETREATING UPPER LOW
OFF THE MID-ATLANTIC COAST. THE FIRST LOW (THE DEEP SOUTH ONE)
WILL ONLY SLOWLY MEANDER EASTWARD, AND ITS POSITIONING WILL SET UP
THE SOUTHEAST WITH DEEP-LAYER SOUTHERLY FLOW, POTENTIALLY ALLOWING
DECENT MOISTURE FLUX INTO THE CAROLINAS. POTENTIALLY IS THE KEY
HERE, BECAUSE THE SAME BOUNDARY THAT WILL HAVE CROSSED THE AREA
FRIDAY MORNING WILL NOW BE STALLING TO OUR SOUTH, AND ENSEMBLES
DO NOT YET HAVE A GOOD GAUGE ON HOW "TOGETHER" IT'LL STAY. THE
OPERATIONAL GFS AND CMC BOTH DEPICT IT KIND OF SMEARING OUT OR AT
LEAST BECOMING SHALLOWER, ALLOWING MOISTURE TO BEGIN RIDING UP OVER
IT IN ANOTHER HYBRID CAD EVENT; THE EC AND MOST OF ITS ENSEMBLES
KEEP MOISTURE SHUNTED FARTHER SOUTH ON FRIDAY NIGHT AND SATURDAY.
THIS PERIOD FROM FRIDAY NIGHT THROUGH THE DAYTIME HOURS ON SATURDAY
IS PROBABLY THE LOWEST-CONFIDENCE PERIOD OF THE FORECAST, BECAUSE
IT'S UNCLEAR HOW MUCH MOISTURE WILL MAKE IT INTO THE WESTERN
CAROLINAS, AND THEREFORE HOW CLOUDY/RAINY IT'LL ACTUALLY BE.
BY SUNDAY, A SORT OF INVERTED TROUGH WILL TRANSLATE NORTH ON THE
LEADING EDGE OF THE UPPER LOW, INCREASING SYNOPTIC FORCING...AND
SO REGARDLESS OF WHERE OR HOW STRONG THE BOUNDARY IS AT THIS POINT,
THIS SHOULD INCITE STRONG ENOUGH ISENTROPIC ASCENT TO START PUMPING
MOISTURE INTO THE AREA. MEANWHILE, THE HIGH WILL HAVE MEANDERED
OFF THE COAST, AND SHOULD LEND SOME SYNOPTIC SUPPORT TO DEVELOPING
HYBRID CAD...WHICH WILL PERSIST THROUGH THE END OF THE PERIOD.
EXPECT BELOW-NORMAL TEMPERATURES AND WIDESPREAD LIGHT RAIN ON
SUNDAY AND MONDAY. THUNDER CHANCES STILL LOOK QUITE LOW THROUGH
THIS PERIOD.
AVIATION /08Z TUESDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: VFR ASIDE FROM FOG IN THE MOUNTAIN VALLEYS
(INCLUDING KAVL). SMALL DEWPOINT DEPRESSIONS AND GENERALLY SIMILAR
PATTERN WOULD SUGGEST FOG IS SIMILARLY LIKELY TO YESTERDAY
MORNING BUT WITH SOME UNCERTAINTY DUE TO STRATOCU AT 060-080
PASSING BETWEEN NOW AND DAYBREAK. PREVAILED MVFR WITH IFR IN
TEMPO. OTHERWISE LARGELY SKC THRU DAYBREAK. KAVL WILL BE MAINLY
NW THRU THE PERIOD WHEN NOT CALM. KCLT SHOULD TREND NW BY THE
FIRST MORNING PUSH BUT OCCASIONAL WSW WINDS PROMPTED INCLUSION OF
AN EARLY TEMPO. DIURNAL CU WILL DEVELOP BY 15-16Z WELL INTO VFR
RANGE. EXCEPT FOR KAVL, WINDS BACK TO WSW OR SW PEAKING AT 8-10
KT DIURNALLY. WINDS DIMINISH THIS EVENING BUT SHOULD TREND BACK
TO NW WHERE NOT CALMING. INCREASING CIRRUS TONIGHT MAKE FOG LESS
LIKELY OVERALL BUT CONFIDENCE LOW FOR RESTRICTIONS ANYWAY.
OUTLOOK: VFR EXPECTED THROUGH WED, BUT THERE APPEAR PERIODIC
CHANCES FOR RESTRICTIONS WED NIGHT THRU SAT.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...WIMBERLEY
NEAR TERM...WIMBERLEY
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...WIMBERLEY
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