065
FXUS62 KGSP 070722
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
322 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 300 AM: CIRRUS SPREADING OVER THE CWA WITHIN REGION OF
DIFFLUENT UPPER FLOW, AND ARGUABLY A WEAK SHORTWAVE, DOWNSTREAM OF
THE UPPER LOW OVER THE SOUTHERN PLAINS. A WARM FRONT IS SETTING UP
NORTH OF I-20 AND WILL ADVECT NORTH AND EAST THRU TODAY. PRECIP
SHIELD EXTENDS ACROSS MUCH OF MS/AL NORTH OF AN MCS NEAR THE
GULF COAST ASSOCIATED WITH A DECAYING MCS; WHILE THE MCS ITSELF
LOOKS TO JUST MISS US TO THE SOUTH IF IT HOLDS TOGETHER, BANDS OF
ENHANCED REFLECTIVITY ARE SEEN THAT SUGGEST WARM FRONTAL PRECIP
IS DEVELOPING VIA THE SAME MOISTURE. THUS, REGARDLESS OF HOW IT
IS BEING GENERATED, PRECIP CHANCES WILL RAMP UP FROM SW TO NE
INTO OUR CWA AFTER 12Z AS THE FRONT SHIFTS NORTH, NO SOONER THAN
PREVIOUSLY FORECAST AND POSSIBLY EVEN A LITTLE LATER. 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. PEAK CHANCES
PEAK AT 50-60% 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 THURSDSAY 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 /08Z WEDNESDAY THROUGH SUNDAY/
AT KCLT AND ELSEWHERE: CIRRUS WILL BE SEEN THRU THE EARLY MORNING
HOURS. 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 OR DRIZZLE, WITH TRUE SHRA MORE LIKELY DEVELOPING
AFTER NOON. CIGS WILL LOWER TO 060-080 BY AROUND 15Z IN THE SC SITES
AND TO MVFR AT KAVL BY AROUND THAT TIME. SOME VARIABILITY MAY RESULT
EARLY ON. PRECIP SHOULD HELP MOISTEN THE INITIALLY DRY LOW LEVELS
AND LEAD TO MVFR CIGS BY AROUND 18Z AT THE SC SITES, WITH PROB30
FOR VSBY AND LOWER MVFR 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 00Z EXCEPT VCSH AT KAVL. LOWERING OF CIGS TO LOWER MVFR IS
EXPECTED TONIGHT AS PRECIP DIMINISHES, ALTHOUGH (EXCEPT AT KAND)
CONFIDENCE ONCE AGAIN TOO LOW TO MENTION IFR, ALTHOUGH IT CAN'T
BE RULED OUT. LIGHT MAINLY NORTHERLY WINDS THRU MID-MORNING THEN
TURNING SW.
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...WIMBERLEY
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...WIMBERLEY
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