251
FXUS62 KGSP 160600
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
100 AM EST SUN FEB 16 2025
SYNOPSIS
A COLD FRONT CROSSES THE AREA TODAY WITH SHOWERS AND PERHAPS
ISOLATED THUNDERSTORMS. BRISK WINDS DEVELOP QUICKLY BEHIND THE
FRONT THIS MORNING AND CONTINUE INTO TONIGHT. DRY HIGH PRESSURE
BUILDS IN MONDAY AND LINGERS THROUGH TUESDAY. ANOTHER LOW
PRESSURE SYSTEM CROSSES THE AREA WEDNESDAY, BRINGING A CHANCE
FOR WINTRY WEATHER. COLD AND DRY HIGH PRESSURE RETURN LATE NEXT
WEEK.
NEAR TERM /THROUGH TODAY/
KEY MESSAGES:
1) AREAS OF DENSE FOG IS FORMING ACROSS MUCH OF THE PIEDMONT,
AND A DENSE FOG ADVISORY HAS BEEN ISSUED THROUGH 5 AM THIS MORNING.
2) WIND ADVISORY FOR THE ENTIRE CWA IN EFFECT FROM EARLY MORNING
THROUGH THE AFTERNOON FOR GUSTY WINDS OF 30-40 MPH EAST OF THE
MOUNTAINS AND 45+ MPH IN THE MOUNTAINS THROUGH EARLY MONDAY MORNING.
3) A COLD FRONT BRINGS LINE OF SHOWERS AND THUNDERSTORMS ACROSS THE
FORECAST AREA THIS MORNING, WITH A NON-ZERO THREAT OF SEVERE STORMS.
4) NW FLOW SNOW POSSIBLE ALONG THE TN/NC BORDER BEHIND THE FRONT.
AS OF 1245 AM EST SUNDAY: THE MAIN FCST CHALLENGE IS FALLING
VISIBILITY, AS A LULL IN PRECIP AND AN ERODING WEDGE IS ALLOWING FOG
TO BECOME DENSE IN SPOTS. HAVE OPTED TO ISSUE A DENSE FOG ADVISORY
FOR THE ENTIRE PIEDMONT THROUGH 5 AM THIS MORNING. THE FOG MAY
LINGER A LITTLE PAST THAT TIME, ESPECIALLY IN THE I-77 CORRIDOR,
IN WHICH CASE IT MAY BE EXTENDED. BUT A LINE OF THUNDERSTORMS
IS STILL ON TRACK TO PUSH INTO THE AREA EARLY THIS MORNING. NO
CHANGES WERE NEEDED TO THE POPS OR THUNDER GRIDS WITH THIS UPDATE.
OTHERWISE...RETREATING SURFACE HIGH PRESSURE MOVING OFF THE
MID-ATLANTIC COAST HELD A HYBRID COLD AIR DAMMING WEDGE THROUGH
AFTERNOON. OFF TO THE WEST, A STRENGTHENING SURFACE LOW WILL LIFT
TOWARD THE NW AND PUSH A STRONG COLD FRONT ACROSS THE CWA EARLY
SUNDAY. WITH THIS VERY BUSY NEAR TERM, LET'S EXAMINE ONE ELEMENT
AT A TIME. BY THIS EVENING AND OVERNIGHT HOURS, THE AREA OF LOW
PRESSURE SHOVES THE HIGH PRESSURE OFFSHORE, HELPING TO ERODE
THE CAD THAT'S BEEN PLAGUING THE AREA. WHAT'S LEFT BEHIND IS
VERY LOW STRATUS AND THE POTENTIAL FOR PATCHY TO EVEN AREAS OF
DENSE FOG AHEAD OF THE FRONT. SURFACE WINDS SHOULD REMAIN LIGHT
TO EVEN CALM EAST OF THE MOUNTAINS THROUGH AT LEAST MIDNIGHT,
CONTRIBUTING TO ANY FOG DEVELOPMENT. THE NEXT ELEMENT TO AFFECT
THE AREA COMES IN EARLY SUNDAY MORNING. A STRONG COLD FRONT PUSHES
THROUGH AND BRINGS WIDESPREAD RAIN, GUSTY WINDS AND THE POTENTIAL
FOR THUNDERSTORMS. THE GOOD NEWS IS THIS FRONT AND LINE OF STORMS
ARE EXPECTED TO QUICKLY SWEEP THROUGH THE AREA AND BY GONE BY
NOON, IF NOT EARLIER. THOUGH THIS SAME LINE IS LIKELY TO PRODUCE
SEVERE WEATHER FOR THE FOLKS FURTHER SOUTH, GUIDANCE IS LIMITING
THE AVAILABLE INGREDIENTS FOR THIS AREA THAT COULD SUPPORT STRONG
THUNDERSTORMS. ALOFT, PLENTY OF SHEAR, 50-70KTS, AND STRONG FORCING
BY THE FRONT ITSELF. AS FOR INSTABILITY, MODELED SOUNDINGS ARE
NOT IMPRESSED AND PLACE ZERO SBCAPE AND VERY LITTLE (0-50 J/KG)
OF MUCAPE. WITHOUT THE INSTABILITY, ESPECIALLY AT THE SURFACE, THE
CHANCE FOR SEVERE WEATHER BECOMES LOW. GIVEN THE SYNOPTIC SETUP
AND OTHER INGREDIENTS IN PLAY, CANNOT RULE OUT DAMAGING WINDS OR
HEAVY RAINFALL WITH THIS FRONTAL PASSAGE. ALL IN ALL, CONFIDENCE
IS LOW TO SEVERE BUT REMAINS NONZERO. THE NEXT ELEMENT OF CONCERN
IS GOING TO BE THE WINDS, ESPECIALLY ACROSS THE MOUNTAINS. GIVEN
THE STRONG SHEAR ALOFT AHEAD OF THE FRONT, WINDS START TO PICK UP
AFTER MIDNIGHT FOR THE NC MOUNTAINS AND BY DAYBREAK ELSEWHERE. WIND
GUSTS OF 30-40 MPH IS LIKELY IN THE UPSTATE AND NC PIEDMONT, WITH
HIGHER GUSTS IN THE MOUNTAINS. FOR THIS A WIND ADVISORY WILL BE
IN EFFECT FOR THE ENTIRE CWA DURING PORTIONS OF THIS NEAR TERM AND
INTO THE BEGINNING OF THE NEXT. WINDS START TO DIMINISH BY SUNDAY
AFTERNOON. THE LAST ELEMENT OF DISCUSSION IS THERE COULD BE SOME
MOISTURE WRAPPING AROUND THE LOW WITH THIS CAA AT THE HIGHER PEAKS,
INDICATING A BIT OF NW FLOW SNOW AT THE TYPICAL TN/NC BORDER. SNOW
AMOUNTS ARE LOW, 1-2" AT MOST. TEMPERATURES TODAY REMAIN BELOW
NORMAL BUT QUICKLY WARM UP TOMORROW AS THE CAD IS ERODED AND THE
AIR IS DRIER.
SHORT TERM /TONIGHT THROUGH TUESDAY/
AS OF NOON SATURDAY: NORTHWEST-FLOW SNOWFALL LOOKS TO CONTINUE INTO
SUNDAY NIGHT WITH SHALLOW MOIST LAYER BANKED AGAINST THE
APPALACHIANS. THE PBL ALONG THE NC/TN BORDER WILL COOL SUCH THAT A
PORTION OF THIS MOISTURE WILL OVERLAP WITH TEMPERATURES IDEAL FOR
DENDRITIC SNOW GROWTH OVERNIGHT THROUGH DAYBREAK MONDAY, WITH
MOISTURE DIMINISHING OVER THE REMAINDER OF THE MORNING. SURFACE TEMPS
WILL BOTTOM OUT IN THE LOWER TO MID TEENS ACROSS THE HIGHER
ELEVATIONS MONDAY MORNING. VERY STRONG WINDS, AVERAGING ABOUT 40-45
MPH IN THE PBL, WILL PERSIST THROUGH SUNDAY NIGHT AS WELL, AND A FEW
GUSTS OF 55-65 MPH ARE POSSIBLE ON RIDGETOPS. WIND CHILLS WILL EASILY
DROP TO AROUND ZERO OR A LITTLE BELOW WHERE THESE WINDS AND TEMPS
OVERLAP, AND A FEW SPOTS MAY MEET THE COLD WX ADVISORY CRITERION
(WIND CHILL -5 TO -14). MAX TEMPS MONDAY WILL BE BUOYED BY
DOWNSLOPING EAST OF THE MOUNTAINS BUT STILL TOP OUT 5-8 DEGREES BELOW
CLIMO UNDER ONGOING CAA. THE MORNING COULD PROBABLY BE DESCRIBED AS
BREEZY ACROSS THE PIEDMONT BUT WELL BELOW WIND ADVISORY CRITERIA.
SNOW WILL TAPER OFF DURING THE MORNING AS THE PBL TRENDS DRIER. DRY
HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE CWA THROUGH TUESDAY AND
POPS REMAINING NEAR ZERO FOR THE REST OF THE SHORT TERM PERIOD. TEMPS
REBOUND TO JUST SLIGHTLY BELOW CLIMO MONDAY NIGHT AND TUE.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
AS OF 100 PM SAT: UPPER LOW WILL CUT OFF OVER THE NORTHERN PLAINS BY
WEDNESDAY MORNING, WITH A LOW AMPLITUDE SHORTWAVE TROUGH ACCELERATING
AHEAD OF IT AND CROSSING THE MID-SOUTH WEDNESDAY. THIS LATTER FEATURE
WILL ADVANCE TO THE NC/VA COAST BY EARLY THURSDAY. GLOBAL MODELS
CONTINUE TO DEPICT MILLER A-TYPE SFC LOW NEAR THE CENTRAL GULF COAST
AT 12Z WED, WHICH TRACKS GENERALLY TO OUR SOUTH THROUGH WEDNESDAY
EVENING. MODELS APPEAR TO BE IN DECENT AGREEMENT ON THIS GENERAL
EVOLUTION. 12Z CYCLE ECMWF, ALONG WITH BOTH EC AND GFS ENSEMBLE
MEANS, HAVE TRENDED TOWARD A SLIGHTLY FASTER DEEPENING OF THE LOW
ALTHOUGH THE TRACK HAS NOT CHANGED MUCH. THE CLOSED UPPER LOW WILL BE
ASSOCIATED WITH A 1050+ MB HIGH OVER EASTERN MONTANA AND VICINITY;
RIDGING WILL EXTEND TO THE MID-ATLANTIC COAST AND CONFLUENCE
DOWNSTREAM OF THE TROUGH MAY LEAD TO A SMALL CLOSED HIGH TO OUR NORTH
SUPPORTING CAD ON WED AND A VERY DRY SFC LAYER.
THE MILLER-A IS LIKELY TO BRING PRECIP SHIELD OVER THE AREA ON WED.
THE CRITICAL DIFFERENCE AMONG MODELS APPEARS TO BE HOW WELL THE
PRECIP OVERCOMES WHAT MAY BE EXCEPTIONALLY DRY AIR AT ONSET, AND HOW
TEMPS RESPOND. THERE ARE SLIGHT DIFFERENCES IN TIMING THAT LIMIT
CONFIDENCE, BUT THESE TEMPERATURE DISCREPANCIES ARE THE MAIN FACTOR
IN A LOW-CONFIDENCE FORECAST, AT LEAST IN THE SENSE OF PRECIP TYPE
TRENDS OR OVERALL IMPACT. THE PRESENCE OF ICE NUCLEI DOES NOT APPEAR
TO BE AN ISSUE AT THE ONSET OF PRECIP, WHICH MOST LIKELY WILL NOT
OCCUR UNTIL AFTER DAYBREAK WEDNESDAY; POPS ARE MAINLY IN THE 10-30%
RANGE TUESDAY NIGHT, REFLECTING POSSIBILITY OF EARLIER ONSET. THE
MOST PLAUSIBLE MIDDLE-GROUND SCENARIO, TAKING THIS INTO ACCOUNT, IS
FOR RAIN OR SNOW EARLY IN THE EVENT, EVEN AFTER POPS RAMP UP INTO THE
LIKELY TO CATEGORICAL RANGE (FROM SW TO NE) DURING THE DAY WED. WITH
LOW CONFIDENCE ON TEMPERATURE, HAVE TRIED TO MINIMIZE THE EXPANSE OF
SUBFREEZING TEMPS EARLY IN THE EVENT, LEAVING MENTION AS A RAIN/SNOW
MIX IN MUCH OF THE CWA WHERE TEMPS HOVER JUST ABOVE FREEZING. A WARM
NOSE MAY ALSO COME INTO PLAY AND SOME SLEET COULD MIX IN AT THIS
TIME. AS THE LOW PASSES THE AREA WED EVENING AND DRYING OCCURS ALOFT,
P-TYPE CHANGES TO FZRA IN PORTIONS OF THE PIEDMONT WHERE TEMPS FALL
BELOW FREEZING; WRAPAROUND MOISTURE KEEPS SNOW GOING OVER THE
MOUNTAINS. MOST PRECIP WILL END WEDNESDAY NIGHT, BUT NW FLOW SNOW
COULD CONTINUE THU ALONG THE TN BORDER.
THE REMAINDER OF THE FORECAST WILL BE DRY AND COLD AS THE ARCTIC AIR
REMAINS OVER THE SOUTHERN US. MIN/MAX TEMPS WILL BE 15-20 BELOW
NORMAL THU-FRI.
AVIATION /06Z SUNDAY THROUGH THURSDAY/
AT KCLT AND ELSEWHERE: A MESSY SET OF TAFS, WITH LIFR TO VLIFR CIGS
AND VSBY EXPECTED ACROSS THE PIEDMONT UNTIL A LINE OF SHRA/TSRA
CROSS THE AREA EARLY THIS MORNING FROM WEST TO EAST. THE LINE
IS EXPECTED TO WEAKEN AS IT ENTERS THE AREA, BUT MAY PRODUCE
GUSTY/ERRATIC WINDS AND BRIEF DOWNPOURS. THE LINE IS BEING HANDLED
WITH TEMPO GROUPS, AS CONFIDENCE IN TIMING INCREASES. VERY STRONG
SW WINDS ATOP AN ERODING WEDGE WILL LIKELY RESULT IN NON-CONVECTIVE
LLWS AT ALL SITES, UNTIL THE CONVECTION ARRIVES. THEN GUSTY SW
WINDS EXPECTED IN WAKE OF A PASSING COLD FRONT. GUSTS MAY BE
STRONG, WITH FREQUENT GUSTS OVER 30 KT FROM LATE MORNING THRU
THE AFTN. CIGS AND VSBY SHOULD IMPROVE THIS MORNING, WITH SKIES
CLEARING OUT IN THE AFTN. WINDS WILL BEGIN TO WEAKEN THIS EVENING,
BUT MAY REMAIN GUSTY. AT KAVL, SW WIND WILL BRIEFLY BE OUT OF THE
W, THEN TOGGLE TO NNW UP THE VALLEY BY MID-AFTN, REMAINING VERY
GUSTY THRU THE EVENING.
OUTLOOK: VFR CONDITIONS EXPECTED MONDAY THRU TUESDAY. THEN A
QUICK-MOVING STORM SYSTEM MAY BRING WINTRY PRECIP AND RESTRICTIONS
TO THE REGION ON WEDNESDAY.
GSP WATCHES/WARNINGS/ADVISORIES
GA...DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
GAZ010-017-018-026-028-029.
WIND ADVISORY FROM 6 AM THIS MORNING TO 6 PM EST THIS EVENING
FOR GAZ010-017-018-026-028-029.
NC...DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
NCZ035>037-056-057-068>072-082-502-504-506-508-510.
WIND ADVISORY FROM 6 AM THIS MORNING TO 6 PM EST THIS EVENING
FOR NCZ035>037-056-057-068>072-082-502-504-506-508-510.
WIND ADVISORY UNTIL NOON EST MONDAY FOR NCZ033-048>053-058-059-
062>065-501-503-505-507-509.
SC...DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
SCZ008>014-019-101>109.
WIND ADVISORY FROM 6 AM THIS MORNING TO 6 PM EST THIS EVENING
FOR SCZ008>014-019-101>109.
SYNOPSIS...WIMBERLEY
NEAR TERM...ARK/CP/PM
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...ARK
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