291
FXUS62 KGSP 071429
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1029 AM EDT WED MAY 7 2025
SYNOPSIS
AN UNSETTLED WEATHER PATTERN DEVELOPS TODAY AND CONTINUES INTO
EARLY NEXT WEEK, WITH OFF-AND-ON RAIN CHANCES EACH DAY.
NEAR TERM /THROUGH TONIGHT/
AS OF 1030 AM EDT WEDNESDAY: NO MAJOR CHANGES TO THE FORECAST AS IT
REMAINS ON TRACK. ONLY MADE MINOR TWEAKS BASED ON CURRENT
OBSERVATIONS AND LATEST MODEL TRENDS AS THE 12Z GUIDANCE TRICKLES IN.
SEEING PRECIP LIFT NORTH INTO THE SOUTHWEST PORTIONS OF THE CFWA,
WHICH HAS LED TO PRECIP CHANCES RAMPING UP IN THE SW HALF OF THE
CFWA THIS MORNING AS A WARM FRONT SHIFTS NORTH INTO THE AREA.
MOISTENING STILL LOOKS TO OCCUR FROM THE TOP DOWN AND PRECIP
INITIALLY MAY BE VERY LIGHT AND AMOUNT ONLY TO SPRINKLES IN SOME
AREAS. WINDS WITHIN THE LAYER OF UPGLIDE ARE WEAK AND MODELS
GENERALLY SHOW ONLY WEAK QPF RESPONSE TODAY. SOME DYNAMIC SUPPORT
DOES ARRIVE WITH THAT WEAK SHORTWAVE THIS AFTERNOON BUT THE STRENGTH
OF THE WAA/UPGLIDE IS JUST NOT VERY IMPRESSIVE BY THAT TIME. POP
TRENDS HAVE BEEN UPDATED PER HRRR WHICH SEEMED TO CAPTURE THE PRECIP
SHIELD FROM THE OVERNIGHT MCS IN THE DEEP SOUTH AND INCORPORATE ITS
MOISTURE INTO THE FRONT. STILL KEPT VALUES NO BETTER THAN ABOUT 60%
IN THE SW ON ACCOUNT OF THE LACK OF CONSISTENCY IN MODELS. MOST
GUIDANCE ACTUALLY NEVER DEVELOPS PRECIP ACROSS THE NW NC PIEDMONT,
WITH THE FRONT SEEMINGLY WASHING OUT. TOTAL PRECIP PROBABLY NOT MORE
THAN A TENTH THRU TODAY. ISOLATED, ELEVATED T-STORMS CAN'T BE RULED
OUT IN THE AFTN OR EARLY EVENING IN THE WEST, WITH PERHAPS AS MUCH
AS 200-300 J/KG FROM ATOP THE FRONTAL INVERSION. TODAY WILL BE
MOSTLY CLOUDY NONETHELESS AND DIABATIC COOLING FROM THE EARLY PRECIP
LOOKS TO KEEP HIGHS SEVERAL DEGREES BELOW NORMAL IN THE SW HALF OF
THE CWA, WITH A GRADIENT TO NEAR-NORMAL TEMPS IN THE NORTHEAST WHERE
LOW CLOUDS TAKE LONGEST TO DEVELOP, IF AT ALL.
DPVA AND DYNAMIC SUPPORT SHIFT FAR ENOUGH EAST LATE IN THE DAY TO
ALLOW A SLIGHT-CHANCE POP ACROSS THE REST OF THE NC PIEDMONT. FLOW
IN THE 850-700 MB LAYER REMAINS WEAK BUT BEGINS TO FAVOR A MORE
WESTERLY DIRECTION, SO WAA WILL WEAKEN AND SLIGHT DOWNSLOPE MAY
PROMOTE SOME DRYING EAST OF THE MOUNTAINS, AND POPS GENERALLY TAPER
OFF A BIT. CHANCE POPS CONTINUE ALONG THE WESTERN AND FAR SOUTHERN
PARTS OF THE CWA. LOW CLOUD COVER MAY PERSIST WITH WEAK INVERSION
TRAPPING MOISTURE IN THE LOW LEVELS. MINS THUS ARE FORECAST A
LITTLE ABOVE NORMAL.
SHORT TERM /THURSDAY THROUGH FRIDAY/
AS OF 214 AM EDT WEDNESDAY...
KEY MESSAGES:
1) THUNDERSTORMS EXPECTED THURSDAY EVENING AND NIGHT, WITH SOME
CHANCE FOR SEVERE WEATHER.
2) AFTERNOON SHOWERS AND THUNDER EXPECTED AGAIN ON FRIDAY, BUT
WITH LOWER SEVERE RISK AND MORE TYPICAL TIMING.
3) VERY WARM TEMPERATURES IN THE LOW TO MID 80S EXPECTED THURSDAY,
FOLLOWED BY COOLER, BUT STILL ABOVE-NORMAL TEMPERATURES ON FRIDAY.
BY THURSDAY MORNING, A HIGHLY ELONGATED TROUGH AXIS RUNNING FROM
THE OZARKS NORTHEAST INTO ONTARIO WILL BEGIN TO PIVOT SOUTHEAST.
THOUGH THE FEATURE LOOKS MORE OR LESS THE SAME IN TONIGHT'S
GUIDANCE AS IT DID LAST NIGHT, IT'S SLOWED DOWN NOTICEABLY,
SUCH THAT APPRECIABLE SYNOPTIC FORCING DOESN'T REALLY ARRIVE
UNTIL THE LATE EVENING. THIS HAS THE EFFECT OF BACKING OFF
THE TIMING OF CONVECTION WELL INTO THE LATE EVENING...WITH PEAK
COVERAGE NOT REALLY DEPICTED UNTIL NEAR MIDNIGHT THURSDAY
NIGHT. AS DPVA RAPIDLY RAMPS UP AND PREFRONTAL MOISTURE ADVECTS
INTO THE AREA, HOWEVER...IT LOOKS LIKE THE MIDLEVELS WILL COOL
RAPIDLY, AND SBCAPE ON THE ORDER OF 800-1000 J/KG WILL BE
MAINTAINED EAST OF THE MOUNTAINS. SO, GIVEN DEEP LAYER SHEAR IN
EXCESS OF 35KTS, SOME CONVECTION CAN BE EXPECTED TO BOTH FORM
AND BECOME ORGANIZED DESPITE ITS LATE TIMING...AND UPSCALE
GROWTH OF AN MCS OVER THE PIEDMONT/UPSTATE IS INDEED WHAT IS
HINTED AT IN THE FINAL HOURS OF THE LATEST NAMNEST AND FV3
CYCLES...THE ONLY CAMS WHICH RUN THIS FAR OUT. WITH ALL THIS IN
MIND, THERE'S CONSIDERABLY BETTER OVERLAP BETWEEN THE SHEAR, THE
INSTABILITY, AND THE CONVECTION ITSELF COMPARED TO EARLIER RUNS
OF THE GLOBAL MODELS...SO THE LIKELIHOOD OF SEVERE WEATHER
THURSDAY NIGHT - PRIMARILY DUE TO WIND AND HAIL - APPEARS TO BE
INCREASING.
ON FRIDAY, WEAK SOUTHERLY FLOW WILL RESUME AT THE LOW LEVELS,
ALLOWING ANOTHER ROUND OF ~1000 J/KG SBCAPE TO DEVELOP.
LAPSE RATES LOOK MORE MARGINAL ON FRIDAY COMPARED TO THURSDAY
(AND SOME GUIDANCE EVEN DEPICTS WEAK ISOTHERMAL LAYER ALOFT,
PERHAPS A RESULT OF SUBTLY-INCREASING HEIGHTS BEHIND THE TROUGH)
AND THE UPPER FLOW WILL BE LESS IMPRESSIVE OVERALL...THOUGH THE
EASTERN ZONES LOOK LIKE THEY MAY STILL WIND UP WITH ~25KTS OF DEEP
LAYER SHEAR DURING THE AFTERNOON. THANKS TO THE FRONTAL PASSAGE,
HOWEVER WEAK IT MAY WIND UP BEING, DEWPOINTS WILL ALSO BE A TOUCH
LOWER THAN ON THURSDAY. SO, THE CASE FOR SEVERE WEATHER ON FRIDAY
AFTERNOON IS A LITTLE LESS CONVINCING, BUT CAN'T BE RULED OUT.
THERE'S HIGHER CONFIDENCE WE'LL AT LEAST BE LOOKING AT SOME SHOWERS,
AND THEIR TIMING LOOKS MORE LIKE THE TYPICAL DIURNAL PEAK.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
AS OF 250 AM EDT WEDNESDAY...
KEY MESSAGES:
1) HYBRID COLD-AIR DAMMING IS EXPECTED TO DEVELOP OVER THE WEEKEND,
RESULTING IN WIDESPREAD STRATIFORM RAINFALL.
2) EXPECT BELOW-NORMAL TEMPERATURES SATURDAY, SUNDAY, AND MONDAY.
3) DESPITE SOME CHANCE OF IMPROVEMENT ON MONDAY, IT LOOKS LIKE
TUESDAY IS THE MOST PROBABLY DAY FOR US TO FINALLY GET RID OF CAD,
AND RETURN TO MORE MAY-LIKE TEMPERATURES.
INCREASING CONFIDENCE ON A WETTER DAY SATURDAY...WITH THE BULK
OF THE LONG-RANGE ENSEMBLES NOW DEPICTING A HYBRID COLD-AIR
DAMMING FEATURE BEGINNING SATURDAY. HIGH PRESSURE WILL BE BE
CENTERED OVER SOUTHERN ONTARIO EARLY IN THE PERIOD, AND WILL
GRADUALLY TRANSLATE INTO EASTERN NEW ENGLAND BY LATE SATURDAY,
WHILE A ROBUST UPPER LOW WILL DEEPEN OVER THE LOWER MISSISSIPPI
VALLEY AND RESULT IN INTENSIFYING MOISTURE FLUX FROM THE GULF.
THIS'LL ALLOW A SLUG OF STRONG ISENTROPIC ASCENT TO PICK UP BY
LATE SATURDAY, WHILE NE SURFACE FLOW SIMULTANEOUSLY PICKS UP AS
THE HIGH FALLS INTO POSITION.
ALL TOLD, IT'S UNCLEAR EXACTLY HOW QUICKLY RAIN WILL BE ABLE TO
OVERCOME A DRY SURFACE LAYER, BUT EXPECT AN ONSET TO STRATIFORM
RAINFALL SOMETIME DURING THE DAYLIGHT HOURS...AND THIS PATTERN
WILL PERSIST THROUGH MOST OF THE REST OF THE PERIOD. MODELS ARE
ALL OVER THE PLACE ON SPECIFICALLY WHEN THE BEST RAIN CHANCES
WILL BE, BUT WARRANT ON-AND-OFF LIKELY POPS ON SUNDAY AND MONDAY.
A SUBSET OF THE GLOBAL ENSEMBLES SUGGEST WE'LL SUCCESSFULLY MIX
OUT ON MONDAY AND PERHAPS DEVELOP SOME AFTERNOON INSTABILITY...BUT
THE HIGH WILL STILL BE PRESENT (IF SLOWLY MOVING OUT OF POSITION)
AND IT SEEMS QUITE UNLIKELY THAT A SYNOPTICALLY-SUPPORTED COLD
WEDGE WILL SUCCESSFULLY MIX OUT WITH ONGOING SHOWERS; SO FOR
NOW, THE THINKING IS THAT WE'LL REMAIN WEDGED IN UNTIL TUESDAY.
BY THEN, THE SUPPORTING HIGH WILL BE WELL EAST OF NEW ENGLAND,
AND WE SHOULD HAVE AN EASIER TIME DEVELOPING A DAYTIME MIXED LAYER
AND SCOURING OUT SOME OF THAT MOISTURE.
AVIATION /15Z WEDNESDAY THROUGH SUNDAY/
AT KCLT AND ELSEWHERE: WEAK WARM FRONTAL LIFT WILL DEVELOP OVER THE
SC SITES OVER THE COURSE OF THE MORNING, WEAK IN NATURE AND LIKELY
RESULTING IN AREAS OF SPRINKLES AT FIRST. PRECIP WILL BE LIGHT
OVERALL. MINOR VSBY RESTRICTIONS POSSIBLE AT THE SC SITES SO HAVE
INCLUDED TEMPO MVFR WITH THE SHRA. HOWEVER, PRIMARILY MIDLEVEL CIGS
IN THOSE AREAS THRU MIDDAY. PRECIP SHOULD HELP MOISTEN THE INITIALLY
DRY LOW LEVELS BUT CONFIDENCE IS LOW AS TO HOW PERSISTENT LOWER
CIGS WILL BE, SO AT KGSP/KGMU/KAVL A PROB30 HANDLES POSSIBILITY OF
LATE DAY RESTRICTIONS. ON ACCOUNT OF THE DRY AIR AND EXPECTATION
THAT THE WARM FRONT WILL WEAKEN BEFORE PUSHING ACROSS THE WHOLE
AREA, CONFIDENCE IS LOW THAT IMPACTFUL PRECIP WILL REACH KCLT OR
KHKY THIS PERIOD AND SO IT HAS BEEN OMITTED FROM TAFS. SIMILARLY
THE MENTION IS DROPPED FROM THE OTHER SITES AFTER LATE EVENING,
EXCEPT VCSH AT KAVL. RESTRICTIONS TONIGHT APPEAR DEPENDENT ON THE
EXTENT OF PRECIP TODAY AND GUIDANCE VARIES WIDELY NEAR DAYBREAK
THU. HENCE ONLY KAVL AND KAND GET RESTRICTIONS, FOR LIKELIHOOD
OF VALLEY FOG AND LONGER DURATION OF PRECIP, RESPECTIVELY. LIGHT
MAINLY NORTHERLY WINDS THRU MID-MORNING THEN TURNING SW BUT WITH
WEAK GRADIENT SUGGESTING CONTINUING VARIABILITY.
OUTLOOK: AN UNSETTLED PATTERN WILL LINGER INTO THE WEEKEND WITH
CHANCES FOR SHOWERS AND RESTRICTIONS.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...WIMBERLEY
NEAR TERM...CAC/WIMBERLEY
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...WIMBERLEY
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