953
FXUS62 KGSP 171155
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
655 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 650 AM TUE: WEAKENING COLD FRONT ASSOCIATED WITH CANADIAN SFC
LOW HAS PROGRESSED THRU MOST OF KY AND MUCH OF TN, AND EMBEDDED
WITHIN BROAD CYCLONIC FLOW AROUND THE PARENT SYSTEM. PER KMRX
VAD, WINDS ARE WSW INTO THE SOUTHERN APPALACHIANS. DESPITE WHAT
HAD APPEARED A SETUP FOR A LONG-DURATION DENSE FOG AND STRATUS
EVENT, IMPROVEMENT IN CIGS/VISIBILITY OCCURRED EARLY THIS MORNING,
PRESUMABLY A RESULT OF DOWNSLOPE FLOW AND WITH THERMAL ADVECTION
HAVING TURNED NEUTRAL ALOFT. HOLDING ONTO DENSE FOG ADVISORY AS-IS
FOR NOW BUT THINK IT MAY BE ABLE TO BE TRIMMED OR EXPIRED IF WE DO
NOT SEE A "SUNRISE SURPRISE" DECLINE IN VSBY. LIGHT WINDS TODAY AND
BREAKS IN HIGHER CLOUD DECKS SHOULD PROMOTE WHOLESALE SCATTERING
AND LIFTING BY LATE MORNING IF NOT SOONER.
RECENT CAMS SEEM TO HAVE KEYED ON AN MCV WITH DECAYED MCS IN GA
MOVING INTO THE SOUTHERNMOST NC MOUNTAINS, 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 /12Z TUESDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: IMPROVEMENT OCCURRED EARLY THIS MORNING
WHEREAS SOLID COVERAGE OF VLIFR HAD BEEN PREVIOUSLY EXPECTED
THROUGHOUT THE REGION, SO 12Z TAFS ARE CONSIDERABLY MORE OPTIMISTIC
THAN BEFORE. WEAK SUBSIDENCE/DOWNSLOPE ON WSW WINDS ALOFT SEEMS
TO BE RESPONSIBLE FOR SAID IMPROVEMENT. NEVERTHELESS, WITH NEARLY
SATURATED SFC CONDITIONS AND SOME AREAS HAVING FILLED BACK IN
WITH VLIFR, HAVE BEEN LIBERAL WITH TEMPOS FOR POSSIBILITY OF A
CRASH AFTER DAYBREAK. KHKY STILL WILL BE BELOW MINIMA AT TIMES TIL
AROUND 14Z. KAVL IS LIKELY TO SEE BRIEF -SHRA THIS MORNING WHICH
ALSO MAY BRING THEM TO IFR FOR A TIME. CHANCE TOO SMALL TO MENTION
ELSEWHERE BUT A SHOWER IS NOT ENTIRELY OUT OF THE QUESTION. LIGHT
SW WINDS WILL INCREASE BY LATE MORNING (EXCEPT KAVL WHICH SHOULD
COME UP FROM NW). CAUTIOUSLY OPTIMISTIC THAT VFR WILL PREVAIL AFTER
THE MORNING STRATUS DISSIPATES. HAVE KEPT A FEW-SCT MENTION AT
MVFR LEVEL MOST OF THE DAY WITH INVERSION PERSISTING AND MOISTURE
PERHAPS BEING ENHANCED BY ISOLATED -SHRA. WINDS WILL BACK ALOFT
AND REINSTATE WAA REGIME TONIGHT. WINDS WILL BE LIGHTER THAN THIS
MORNING, AND MIXING PROBABLY WILL NOT BE VERY EFFECTIVE TODAY AT
DRYING THE PBL. HENCE LOW STRATUS AND FOG ARE EXPECTED ACROSS THE
REGION AGAIN TONIGHT, WITH LIFR GENERALLY LIKELY AFTER MIDNIGHT,
EXCEPT KAVL WHICH PROBABLY WILL BE ONLY IFR.
OUTLOOK: AN UNSETTLED PATTERN CONTINUES THROUGH EARLY THURSDAY, WHEN
A COLD FRONT FINALLY BRINGS IN 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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