817
FXUS62 KGSP 070616
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
216 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 155 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. PRECIP SHIELD EXTENDS
ACROSS MUCH OF MS/AL NORTH OF AN MCS NEAR THE GULF COAST; IF THIS
HOLDS TOGETHER LONG ENOUGH VERY LIGHT PRECIP COULD ADVECT INTO OUR
GA ZONES AROUND DAYBREAK. A WARM FRONT IS SETTING UP NORTH OF I-20
AND WILL ADVECT NORTH AND EAST THRU TODAY. HARD TO SAY FOR CERTAIN
FROM RADAR MOSAIC BUT IT APPEARS THERE MAY BE SOME PRECIP BEGINNING
TO DEVELOP OVER THE FRONT IN AL. PRECIP CHANCES WILL RAMP UP FROM
SW TO NE INTO OUR CWA AFTER 12Z VIA THE FRONT, 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. WINDS IN 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. MOST
GUIDANCE ACTUALLY NEVER DEVELOPS PRECIP ACROSS THE NW NC PIEDMONT,
WITH THE FRONT SEEMINGLY WASHING OUT. 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.
DETAILS FORTHCOMING ABOUT TONIGHT.
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 230 PM EDT TUESDAY: A WET PATTERN SETS UP FOR MUCH OF THE LONG
TERM. THE NORTHERN UPPER LOW QUICKLY MOVES EAST AS THE SOUTHERN LOW
DEEPENS AND REMAINS NEARLY STATIONARY OVER THE LOWER MS RIVER
VALLEY. WAVES OF LOW PRESSURE MOVE ALONG THE FRONTAL BOUNDARY
STALLED TO OUR SOUTH. THIS BRINGS PERIODS OF MOISTURE AND ISENTROPIC
LIFT TO THE AREA EACH DAY. THE UPPER LOW LIFTS INTO MIDDLE TN
TUESDAY WITH A CONSOLIDATING SURFACE LOW MOVING INTO THE SOUTHEAST.
PERIODS OF MOIST, SOUTHEASTERLY FLOW COULD BE EXPECTED WITH CLOUDS
AND PERIODS OF RAIN SATURDAY AND SUNDAY IN A COLD AIR DAMMING-LIKE
CONFIGURATION WHICH COULD LINGER INTO MONDAY. THE CAD COULD ALSO
ERODE AS EARLY AS MONDAY WITH ISOLATED THUNDERSTORMS DEVELOPING IN
WEAK INSTABILITY. EROSION WOULD LOOK MORE LIKELY TUESDAY WITH THE
LOWS ON THE MOVE EASTWARD, LEADING TO INCREASING CONVECTIVE CHANCES.
WHETHER THIS WOULD LEAD TO SEVERE STORM POTENTIAL IS HIGHLY
UNCERTAIN. PERIODS OF HEAVY RAINFALL WOULD BE MORE LIKELY, BUT UPPER
LOWS ARE NOTORIOUSLY FICKLE, SO THIS IS UNCERTAIN AS WELL. NEAR TO
BELOW NORMAL TEMPS WOULD BE EXPECTED FOR THE WEEKEND CREEPING BACK
UP TOWARD NORMAL BY TUESDAY.
AVIATION /06Z 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...RWH
AVIATION...WIMBERLEY
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