153
FXUS62 KGSP 170829
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
329 AM EST TUE DEC 17 2024
SYNOPSIS
CLOUD COVER WILL PERSIST TODAY AS A FRONT STALLS IN THE AREA, ALONG
WITH SCATTERED SHOWERS OVER THE MOUNTAINS. TEMPS WILL BE ABOVE
NORMAL TODAY AND WEDNESDAY, WITH A STRONGER FRONT APPROACHING
FROM THE WEST AND INCREASING RAIN CHANCES AREA-WIDE WEDNESDAY
AFTERNOON AND EVENING. COOLER CONDITIONS ARE EXPECTED BEHIND THE
FRONT THROUGH THE WEEKEND.
NEAR TERM /THROUGH TONIGHT/
AS OF 250 AM TUE: WEAKENING COLD FRONT ASSOCIATED WITH CANADIAN
SFC LOW HAS PROGRESSED ABOUT HALFWAY ACROSS KY/TN, AND EMBEDDED
WITHIN BROAD CYCLONIC FLOW AROUND THE PARENT SYSTEM. PER KMRX VAD,
WINDS ARE WSW INTO THE SOUTHERN APPALACHIANS. WITH THAT AND ABUNDANT
NEAR-SFC MOISTURE, CAN'T RULE OUT LIGHT PRECIP OR DRIZZLE ALONG THE
TN/NC BORDER THIS MORNING. THE REMAINDER OF THE CWA IS PROBABLY
EXPERIENCING VIRTUALLY NEUTRAL THERMAL ADVECTION, BUT NOT ENOUGH
TO PROMOTE EROSION OF THE REMNANT COLD POOL FROM SUNDAY'S CAD
EVENT. HENCE WE STILL EXPECT A SOUPY MORNING WITH LOW CLOUDS AND
FOG GENERALLY LINGERING THRU THE MORNING COMMUTE. SOME IMPROVEMENT
IN THE FOG CONDITIONS HAVE BEEN NOTED IN PARTS OF THE PIEDMONT,
PERHAPS A RESULT OF VERY WEAK DOWNSLOPE FLOW, BUT THINK BY AND
LARGE DENSE FOG ISN'T GOING ANYWHERE SOON. HOLDING ONTO DENSE FOG
ADVISORY AS-IS FOR NOW. LIGHT WINDS TODAY AND BREAKS IN HIGHER CLOUD
DECKS SHOULD PROMOTE SCATTERING AND LIFTING BEGINNING LATE MORNING.
FARTHER SOUTH JUST AHEAD OF THE FRONT, A WEAKENING MCS IS SEEN IN
MS/AL. RECENT CAMS SEEM TO HAVE KEYED ON AN MCV WITH THIS ACTIVITY
ADVECTING INTO THE SOUTHERNMOST NC MOUNTAINS LATER TODAY, AND IN
TURN VARIOUSLY PRODUCE SOME SMALL QPF RESPONSE NEAR THE SOUTHERN
BORDER OF NC (EVEN EAST OF THE MOUNTAINS) DURING THE LATE MORNING
TO EARLY AFTERNOON. THIS IS REFLECTED IN SLIGHTLY HIGHER POPS IN
THAT AREA TODAY THAN ON THE PREVIOUS FORECAST. STILL NOT KEEN ON
GOING HIGHER THAN SLIGHT-CHANCE/ISOLATED EAST OF THE MOUNTAINS
DUE TO THE BEST MOISTURE BEING UNDER THE SUBSIDENCE INVERSION;
FURTHERMORE THE MINIMAL MUCAPE SUGGESTED BY MODELS LOOKS SHALLOW
AND/OR INHIBITED. SLIGHT-CHANCE TO LOW CHANCE RANGE POPS ARE BEING
MAINTAINED FOR THE MOUNTAINS MAINLY AS A RESULT OF UPSLOPE LIFT;
STILL EXPECT THE SFC FRONT WILL STALL FROM EAST TN TO SOUTHWEST
VA AND KEEP THE FOOTHILLS/PIEDMONT IN THE NEUTRAL TO VERY WEAK WAA
REGIME. TEMPERATURES STILL SHOULD REBOUND INTO THE 60S, EVEN WHERE
THE EFFECTS OF THE COLD POOL AND STRATUS HANG ON THE LONGEST. MOST
PIEDMONT AREAS WILL RISE INTO THE UPPER 60S.
THE APPROACH OF A SHORTWAVE INTO THE OZARK REGION STILL IS EXPECTED
TO BACK LOW LEVEL FLOW TO SOUTHERLY AND REACTIVATE THE STALLED
FRONT. THE BEST RESULTING FORCING APPEARS OVER THE NORTHERN PART
OF THE CWA, SO POPS TAPER A BIT IN THE MOUNTAINS FOR A TIME AND
INCREASE TO A SOLID SLIGHT-CHANCE IN AREAS NORTH OF I-40 OVERNIGHT
TONIGHT, AND IN OUR EAST WHERE MOIST MARITIME AIR MAY ADVECT. THE
COLD POOL NOT BEING LIKELY TO GO COMPLETELY AWAY TODAY, AND WITH
LIGHT WINDS AND NEAR-SFC WARM/MOIST ADVECTION, AREAS OF FOG ARE
EXPECTED ACROSS MOST OF THE PIEDMONT ONCE AGAIN. ANOTHER DENSE FOG
ADVISORY MAY BE NEEDED BUT PER USUAL WE WOULD SEEK TO ISSUE THAT
THIS EVENING ONCE WE HAVE CONFIDENCE EXACTLY WHERE. MINS AGAIN
WILL BE CONSIDERABLY ABOVE NORMAL, MOSTLY NEAR 50.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
AS OF 150 AM EST TUESDAY: LONGWAVE UPPER TROUGH WILL DIG ACROSS
FROM THE CENTRAL CONUS TO THE EASTERN SEABOARD DURING THE DAY
WEDNESDAY, WHILE THE STALLED FRONT DRAPED OVER THE AREA BEGINS TO
LIFT NORTH OVERNIGHT TUESDAY INTO WEDNESDAY AS WEAK CYCLOGENESIS
WILL UNDERWAY NEAR THE BASE OF THE TROUGH AND ACTIVATE A SURFACE
LOW ALONG THE ATTENDANT FRONTAL BOUNDARY, WHICH IN TURN ALLOWS FOR
WARM FRONTAL ACTIVATION TO TAKE PLACE WITHIN THE STALLED FRONT. DEEP
LAYER SOUTHWESTERLY FLOW SUGGESTS THAT VERTICAL PROFILES GRADUALLY
BECOME SATURATED, BUT DRY AIR ABOVE THE BOUNDARY LAYER MAY PUT A
CAP IN WIDESPREAD SHOWER/THUNDERSTORM COVERAGE, ESPECIALLY SINCE
THE ASSOCIATED DPVA LAGS BEHIND THE FRONT, WITH NOT MUCH EVIDENCE
FOR PRE-FRONTAL FORCING AS THE COLD FRONT ENTERS THE CFWA WEDNESDAY
AFTERNOON/EVENING. AS A RESULT, LOW-END POPS AND LIGHT QPF RESPONSE
FOR LOCATIONS EAST OF THE MOUNTAINS ON WEDNESDAY BEFORE THE FROPA
OCCURS. STILL EXPECT OROGRAPHICALLY ENHANCED PRECIPITATION TO
DEVELOP ACROSS THE MOUNTAINS AHEAD AND ALONG THE FRONT WILL ALLOW
FOR CONVECTION TO INITIATE DURING THE DAY WEDNESDAY, WITH ALL LIQUID
P-TYPES AS TEMPERATURES ARE WAY TOO WARM ALONG AND AHEAD OF THE COLD
FRONT. THE COLD FRONT WILL COMPLETE A FULL FROPA LATER WEDNESDAY
EVENING, BUT NORTHWEST FLOW PRECIP MAY PERSIST IMMEDIATELY BEHIND
THE FRONT ALONG THE NC/TN BORDER AS THE ASSOCIATED VORT LOBE LAGS
BEHIND WITH FALLING TEMPERATURES. THE COLD AIR WILL CHASE THE PRECIP
AND MAY PROVIDE ONLY A BRIEF PERIOD FOR SNOW BEFORE DRY AIR
ENTRAINMENT FILTERS IN, WITH LITTLE TO NO SNOW ACCUMULATION
EXPECTED. COMPRESSIONAL WARMING AHEAD OF THE FRONT AND BEING
SITUATED WITHIN THE WARM SECTOR AHEAD OF THE ATTENDANT COLD FRONT
WILL LEAD TO AFTERNOON HIGHS ON WEDNESDAY TOPPING OUT 10-15 DEGREES
ABOVE NORMAL.
WEAK HIGH PRESSURE MOVES IN BEHIND THE FRONT WEDNESDAY NIGHT INTO
THURSDAY WITHOUT ANY SIGNIFICANT HEIGHT FALLS. THE SENSIBLE WEATHER
WILL BE QUIET, BUT THE AIRMASS REMAINS RATHER MILD CONSIDERING A
COLD FRONT PASSAGE DURING THE MONTH OF DECEMBER. AFTERNOON HIGHS
WILL BE AT OR SLIGHTLY ABOVE NORMAL FOR MOST LOCATIONS. A STRONG
SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW WILL BE BARRELING
TOWARDS THE MIDWEST AND OH VALLEY THURSDAY NIGHT, IN AN ALBERTA
CLIPPER TYPE FASHION. RAPID HEIGHT FALLS WILL ACCOMPANY THIS
SHORTWAVE TO GO ALONG WITH WEAK MOISTURE ADVECTION AHEAD OF THE
TROUGH, WHICH SHOULD PRODUCE OROGRAPHICALLY ENHANCED CLOUD COVER
ALONG THE NC/TN BORDER THURSDAY NIGHT, BUT NOT ENOUGH TO SQUEEZE
OUT MEASURABLE POPS. OTHERWISE, OVERNIGHT LOWS THURSDAY WILL BE
SLIGHTLY ABOVE NORMAL AS THE BOUNDARY LAYER STRUGGLES TO FULLY
DECOUPLE AND INCREASING CLOUD COVER MOVES IN ACROSS THE AREA AHEAD
OF THE SHORTWAVE AS A SHALLOW LOW-LEVEL MOISTURE LAYER LINGERS
UNDERNEATH A NOCTURNAL INVERSION.
LONG TERM /FRIDAY THROUGH MONDAY/
AS OF 315 AM EST TUESDAY: SHORTWAVE TROUGH WILL BE IN THE MIDST OF
SWEEPING ACROSS THE EAST COAST ON FRIDAY, WITH THE AXIS PUSHING
EAST OF THE AREA BY FRIDAY NIGHT. NORTHWEST FLOW PRECIP IS
EXPECTED TO DEVELOP BEHIND THE TROUGH AS MECHANICAL LIFT ON THE
FAVORABLE NORTHWEST FACING SLOPES ALONG THE NC/TN BORDER WILL BE
IN PLAY. PROFILES FROM VARIOUS MODEL GUIDANCE WILL BE COLD ENOUGH
TO SUPPORT SNOW, BUT NOT ALL PROFILES SHOW ENOUGH SATURATION TO
TAP INTO THE DENDRITIC GROWTH ZONE. THIS WILL LIMIT ANY DECENT
SNOWFALL ACCUMULATIONS CONSIDERING THE ANTECEDENT DRY CONDITIONS
PRIOR TO THE SHORTWAVE PASSAGE AND FOR THE POTENTIAL OF RIME ICE
TO LIMIT OVERALL SNOWFALL AMOUNTS AS WELL. DETERMINISTIC MODELS
AND ENSEMBLE MEAN BARELY SHOW UP TO AN INCH OF SNOW BEFORE WINDS
SHIFT MORE NORTH TO NORTHEASTERLY SATURDAY NIGHT AS THE SURFACE
HIGH MOVES ACROSS THE GREAT LAKES AND ESSENTIALLY SHUTS OFF ANY
NORTHWEST FLOW PRECIP. EXPECT TEMPERATURES TO DIP 5-10 DEGREES BELOW
NORMAL OVER THE WEEKEND AS COLDER AIR ALOFT SETTLES OVERHEAD AND CAA
FILTERS IN BEHIND THE SHORTWAVE ON SATURDAY. SUNDAY INTO THE EARLY
PART OF NEXT WEEK, MODEL GUIDANCE SHOW A WEDGE-LIKE CONFIGURATION
FROM A SYNOPTIC STANDPOINT AS A STRONG SURFACE HIGH (~1035-1040MB)
SETS UP SHOP OVER THE NORTHEASTERN CONUS AND NORTHEASTERLY FLOW
NOSES INTO THE REGION.
AVIATION /09Z TUESDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: NO APPRECIABLE CHANGE IN FLIGHT CATEGORY
AT THE SC SITES OR KHKY UNTIL FOG LAYER BEGINS TO MIX OUT, WHICH
STILL LOOKS TO OCCUR 14-15Z. CONDITIONS THERE ARE LIKELY TO REMAIN
BELOW MINIMA, EVEN WITH A LIGHT WIND AT KGSP/KGMU. KCLT SHOULD
REMAIN BELOW MINIMA ALTHOUGH IT IS CLOSER TO THE EDGE OF THE DECK,
AND WIND HAS BEEN ASSOCIATED WITH SOME BRIEF IMPROVEMENT THERE,
HENCE TEMPO. AT KAVL, STARTING OFF VFR, BUT A BAND OF LIGHT PRECIP
AHEAD OF A STALLING FRONT MAY BRING A PERIOD OF MVFR WHICH PROBABLY
THEN WILL LINGER THRU DAYBREAK.
SFC WINDS WILL BE PREDOMINANTLY SW WHEN BLOWING AT ALL SITES EXCEPT
KAVL. AS WINDS TURN MORE WESTERLY ALOFT, KAVL PROBABLY WILL TURN
TO NW, AND UPSLOPE GENERATED CLOUDS ARE LIKELY TO BE SEEN THERE
MUCH OF THE REMAINDER OF THE MORNING. ELSEWHERE, ONCE FOG LAYER
DISSIPATES TODAY, CLOUDS ARE EXPECTED TO REMAIN AT MVFR FOR MOST
OF THE DAY, TRAPPED UNDER INVERSION, ALTHOUGH THEY PROBABLY WILL
SCATTER TO VFR LATE. THE FRONT STALLS AND REACTIVATES OVER NORTHERN
NC TONIGHT, WITH ANOTHER LIFR DECK AND AREAS OF IFR TO LIFR FOG
LIKELY TO DEVELOP AFTER MIDNIGHT.
OUTLOOK: AN UNSETTLED PATTERN CONTINUES THROUGH EARLY THURSDAY,
WHEN A COLD FRONT FINALLY INDUCES A CHANGE TO A DRIER CONTINENTAL
AIRMASS. PERIODIC RESTRICTIONS ARE LIKELY THROUGH THEN. GENERALLY
DRY AND VFR TO END THE WEEK.
GSP WATCHES/WARNINGS/ADVISORIES
GA...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR GAZ017-018-
026-028-029.
NC...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR NCZ035>037-
056-057-068>072-502-504-506-508-510.
SC...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR SCZ008>014-
019-104>109.
SYNOPSIS...WIMBERLEY
NEAR TERM...WIMBERLEY
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...WIMBERLEY
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