403
FXUS62 KGSP 161759
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1259 PM EST MON DEC 16 2024
SYNOPSIS
DRIER TODAY WITH RAIN CHANCES RETURNING FOR THE MOUNTAINS TONIGHT
INTO TUESDAY AHEAD OF AN APPROACHING COLD FRONT. WELL ABOVE NORMAL
TEMPERATURES ARE EXPECTED TUESDAY INTO WEDNESDAY, WITH A COLD FRONT
INCREASING RAIN CHANCES AREA-WIDE WEDNESDAY AFTERNOON AND EVENING.
DRIER CONDITIONS ARE EXPECTED THE REST OF THE WEEK, OUTSIDE OF SOME
LIGHT NORTHWEST FLOW SNOW SHOWERS FRIDAY NIGHT INTO EARLY SATURDAY,
WITH A GRADUALLY COOLING TREND EXPECTED THROUGH THE WEEKEND.
NEAR TERM /THROUGH TONIGHT/
AS OF 1247 PM EST MONDAY: EXTENSIVE LOW CLOUDS CONTINUE TO BLANKET
MOST OF THE FCST AREA EARLY THIS AFTERNOON, AND WILL PROBABLY
PERSIST WELL INTO THE AFTERNOON ACROSS MOST OF THE PIEDMONT AND
FOOTHILLS OF THE CAROLINAS, AND NEVER GO AWAY COMPLETELY IN THE
NC FOOTHILLS. TEMPS WILL BE MODULATED BY WHERE WE MANAGE TO THIN
OUT THE CLOUDS. NO REASON TO MAKE ANY CHANGES JUST YET.
OTHERWISE...SYNOPTICALLY, THE CLASSICAL COLD AIR DAMMING REGIME IS
BREAKING DOWN AS THE LARGE AND STRONG SURFACE HIGH HAS SLIGHTLY
WEAKENED AND IS NOW CENTERED OFFSHORE THE NEW ENGLAND COAST. THE
SURFACE HIGH LOOKS TO BECOME COMPLETELY CUT OFF FROM NOSING
INTO THE REGION AS A PROMINENT OPEN SHORTWAVE SLIDES ACROSS THE
NORTHEAST AND HELPS PUSH THE HIGH EVEN FURTHER OFFSHORE LATER
THIS MORNING. THIS WILL ALLOW FOR THE SENSIBLE WEATHER TO REMAIN
MOSTLY DRY OUTSIDE OF A FEW PATCHES OF DRIZZLE. WHILE THE SYNOPTIC
PATTERN ISN'T SUPPORTIVE OF ONGOING CAD, THERE IS ALSO A LACK
OF A MECHANISM FOR TRUE EROSION OF THE DOME OF COLD AIR. A FLAT
UPPER RIDGE WILL MOVE ACROSS THE AREA DURING THE DAY AS THE FLOW
BECOMES WESTERLY, BUT 850MB WINDS OUT OF THE SOUTHWEST DOESN'T
SUPPORT A DOWNSLOPE MECHANISM EAST OF THE MOUNTAINS. WINDS ATOP THE
INVERSION LAYER WON'T BE STRONG ENOUGH TO HELP MIX OUT THE WEDGE,
SO WILL HAVE TO RESULT TO MIXING OUT FROM THE EDGE OF THE WEDGE. OF
COURSE THIS PROCESS IS MUCH SLOWER AND WILL HELP THE WEDGE LINGER
WELL INTO THE AFTERNOON, ESPECIALLY ACROSS THE NORTHERN UPSTATE,
NORTHEAST GEORGIA, AND NC FOOTHILLS. WOULDN'T BE SURPRISED IF THESE
LOCATIONS STRUGGLE TO GET OUT OF THE 40S FOR AFTERNOON HIGHS, BUT
LOCATIONS THAT ARE ABLE TO SCATTER OUT ON THE EDGE OF THE WEDGE
WILL HAVE THE OPPORTUNITY TO PUSH INTO THE MID TO UPPER 50S FOR
HIGHS, BASICALLY SOUTH OF I-85. THIS SETUP LIKELY CREATES A TIGHT
TEMPERATURE GRADIENT WHERE SOMEWHERE LIKE GREENVILLE, SC WILL ONLY
GET TO AROUND 50, WHILE GREENWOOD, SC REACHES THE 60 DEGREE MARK
FOR MAX TEMPERATURES.
A NEGATIVELY TILED UPPER TROUGH WILL SWING ACROSS THE EASTERN
CANADIAN PROVINCES TODAY INTO TONIGHT WITH AN ATTENDANT FRONTAL
BOUNDARY THAT WILL BE KNOCKING ON THE DOOR OF THE NC/TN BORDER
OVERNIGHT TONIGHT. POPS WILL UPTICK ALONG AND NEAR THE NC/TN
BORDER TONIGHT, BUT WON'T BE ABLE TO MAKE MUCH MORE PROGRESSION
BY THE END OF THE PERIOD AS THE BOUNDARY BECOMES MORE PARALLEL
TO THE MEAN FLOW AS THE UPPER TROUGH AND PARENT LOW MOVES EAST OF
THE HUDSON BAY AND THE TRAILING FRONT SLOWLY WEAKENS AS THE BETTER
FORCING WILL BE WELL TO THE NORTHEAST BY DAYBREAK TUESDAY. WITH THE
INVERSION LAYER IN PLACE AND LOW-LEVEL MOISTURE STILL AVAILABLE,
EXPECT LOW STRATUS TO BECOME WIDESPREAD ACROSS THE AREA AGAIN
OVERNIGHT TONIGHT. OVERNIGHT LOWS WILL RUN 10-15 DEGREES ABOVE
NORMAL THANKS TO EXTENSIVE CLOUD COVER.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
AS OF 130 AM MON: AT THE SURFACE, A COLD FRONT LOOKS TO STALL JUST AS
IT REACHES THE NC MOUNTAINS TUESDAY MORNING, ALTHOUGH SOME ASSOCIATED
CONVERGENCE WILL DEVELOP EAST OF THE MOUNTAINS AT/ABOVE 925MB.
PARTIAL CLOUD COVER IS LIKELY TO LINGER IN THIS ZONE, SHIFTING
SOUTHEAST THROUGH THE CWA OVER THE COURSE OF THE DAY. VEERING FLOW
HOWEVER WILL RESULT IN DOWNSLOPING AND SOME DEGREE OF LOW LEVEL
DRYING AND CLEARING IN THE LEE OF THE MOUNTAINS AND EVENTUALLY IN THE
NORTHERN NC PIEDMONT. THE DOWNSLOPE FLOW ALSO WILL PROMOTE WARMING,
SUCH THAT HIGHS IN THE MOUNTAIN VALLEYS AND PIEDMONT SHOULD WARM INTO
THE MID 60S, PERHAPS EVEN WARMER IN THE PIEDMONT AREAS WHICH SEE MORE
SUNSHINE. RELUCTANT TO GO AS WARM AS MOS, WHICH NORMALLY WOULD BE A
DECENT CHOICE IN A DOWNSLOPE SITUATION, KNOWING WE WILL BE COMING OUT
OF CAD AND AN INVERSION STILL IS PROGGED TO PERSIST THROUGH THE DAY.
IT CONTINUES TO LOOK LIKE THE STALLED FRONT WILL REACTIVATE TUESDAY
NIGHT AS THE TRAILING HIGH MIGRATES TOWARD THE MID-ATLANTIC COAST AND
FULL-LATITUDE TROUGH WITH EMBEDDED SHORTWAVE SWINGS ACROSS THE
PLAINS. SOUTHERLY FLOW AND WEAK WARM UPGLIDE WILL CONTINUE ALTHOUGH
THE BETTER MOISTURE WILL SHIFT NORTHWARD, AND IN FACT DRYING IS SHOWN
TO OCCUR IN MIDLEVELS, WITH AIR FLOWING FROM THE DRY/SUBSIDENT INLAND
EXTENSION OF THE WESTERN ATLANTIC HIGH OVER GA/AL. PRECIP CHANCES
PERSIST OVER THE MOUNTAINS DUE TO MECHANICAL LIFT AND SHALLOW MOIST
LAYER.
MEANWHILE, CYCLOGENESIS WILL BE ALREADY UNDERWAY NEAR THE BASE OF THE
TROUGH AND WILL CONTINUE INTO WED AS THE TROUGH MOVES TOWARD THE
LOWER OHIO VALLEY. MODELS FEATURE THE INCIPIENT LOW SKIRTING BY TO
OUR NORTHWEST VERY SIMILAR TO HOW IT HAS PREVIOUSLY APPEARED. THE
TIMING HOWEVER HAS INCREASED A BIT ON RECENT RUNS AND THE LOW
SLIGHTLY STRONGER. 850MB WINDS INCREASE TO AROUND 30 KT AND WINDS
THUS BECOME BRISK AT HIGH MOUNTAIN ELEVATIONS. THE AFOREMENTIONED DRY
AND WARM LAYER ABOVE THE PBL HOWEVER WOULD APPEAR TO HINDER
PRECIPITATION AND CONVECTION THRU DIURNAL HEATING. COLD FRONT SHOULD
REACH THE TN/NC BORDER LATE IN THE DAY, WITH DEEP MOISTURE AND
DEVELOPING UPSLOPE FLOW SUGGESTING HIGH POPS BUT STILL PROBABLY WELL
UNDER AN INCH OF QPF. IT'S A DIFFERENT STORY IN THE LEE OF THE
MOUNTAINS WHERE THE DRIER AIR WILL PERSIST ALOFT. LOW-LEVEL MOISTURE
INCREASES INTO SOME OF OUR PIEDMONT THRU EVENING, SEEMINGLY AS
MARITIME AIR ADVECTS UP FROM THE COASTAL PLAIN, BUT THE COLUMN NEVER
SATURATES SO POPS WILL REMAIN COMPARATIVELY LOW THERE AND QPF SMALL
ACROSS THE BOARD. THE FROPA IS EXPECTED IN THE MOUNTAINS IN THE
EVENING AND IN THE MIDDLE OF THE NIGHT FOR THE PIEDMONT. PRECIP WILL
BRIEFLY TRANSITION TO NW FLOW IN THE MOUNTAINS BUT PROBABLY WILL END
BEFORE TEMPS COOL ENOUGH FOR SNOW, WITH ALL POPS BELOW SLIGHT-CHANCE
BY EARLY THU MORNING. MINS WILL TREND COOLER ALTHOUGH REMAIN ABOVE
NORMAL THEN.
LONG TERM /THURSDAY THROUGH SUNDAY/
AS OF 300 AM MON: MAIN FEATURE OF INTEREST FOR THE LATE WEEK REMAINS
A SHORTWAVE AND SFC LOW ACTUALLY OF PACIFIC ORIGIN, BUT TAKING A
SIMILAR TRACK TO AN ALBERTA CLIPPER AS IT BLOWS THROUGH OUR REGION.
THE SHORTWAVE AXIS REACHES THE MOUNTAINS EARLY FRIDAY FOLLOWED
QUICKLY BY A COLD FRONT. OPERATIONAL GFS AND EC ACTUALLY INDUCE WARM
UPGLIDE AHEAD OF THE SHORTWAVE, ENOUGH TO WARRANT A MENTION OF
PARTIAL CLOUD COVER THU NIGHT AND FRI ALTHOUGH NO POP EAST OF THE
MOUNTAINS. DYNAMIC SUPPORT WILL BE BRIEF AND MAINLY CONFINED TO
FRIDAY NEAR THE TN BORDER WHEN PRECIP BECOMES POSSIBLE--RAIN OR SNOW
DEPENDENT ON SFC TEMP OR TW. A PERIOD OF NW FLOW ENSUES BEHIND THE
FRONT WHICH MAY ALLOW SNOW SHOWERS TO CONTINUE FRIDAY NIGHT.
MOISTURE IS SHALLOW AND ENSEMBLE SPREAD WIDE IN TERMS OF PROFILES,
SO POPS ARE BEING KEPT TO AN ISOLATED OR SLIGHT-CHANCE MENTION AND
ACCUMULATION IS MINIMAL. AT LEAST FLURRIES MAY LINGER INTO SATURDAY.
OTHERWISE THE AREA WILL EXPERIENCE MOSTLY CLEAR AND COLD CONDITIONS
FRIDAY NIGHT AND THRU THE WEEKEND.
TEMPERATURES WILL BE CONSIDERABLY COOLER THU COMPARED TO WED,
TRENDING COOLER BEHIND THE FRONT SUCH THAT MINS/MAXES SHOULD BE A FEW
BELOW NORMAL SATURDAY, AND 10-15 BELOW NORMAL ON SUNDAY.
AVIATION /18Z MONDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: A TYPICAL SITUATION ACROSS THE REGION THIS
AFTERNOON WITH A REMNANT COOL POOL AND EXTENSIVE LOW CLOUDS LEFTOVER
FROM A COLD AIR DAMMING WEDGE. KAVL SHOULD STAY MAINLY VFR THRU THE
EVENING, BUT A TEMPORARY MVFR CEILING IS POSSIBLE. ON THE OTHER
END OF THE COOL POOL IS KCLT, WHICH STILL HAS A SHOT AT BRIEF
IMPROVEMENT IN THE LATE AFTERNOON. UNTIL THEN, LIFR CEILING WILL
PERSIST WITH IFR/MVFR HOLES. THE REST OF THE TERMINALS WILL STAY IN
THE CLOUDS FOR THE DURATION WITH CONTINUED LIFR/IFR CEILING. EVEN
KCLT WILL SEE A RETURN OF THE IFR TO LIFR CEILING ONCE THE SUN
GOES DOWN, WHICH IS A SAFE BET IN THESE CIRCUMSTANCES. WIND WILL
REMAIN LIGHT S. THE BIG QUESTION FOR TONIGHT IS HOW BAD DOES THE
CEILING/VIS GET? THE SET-UP IS NOT EXACTLY THE BEST FOR DENSE FOG,
BUT SOME OF THE GUIDANCE SUGGESTS A PERIOD OF VLIFR EAST OF THE
MOUNTAINS IN THE LATE EVE TO PRE-DAWN HOURS. WE WILL RESIST THIS
FOR THE TIME BEING BECAUSE OF CONFIDENCE ISSUES, AND BECAUSE OFTEN
THE GUIDANCE BACKS OFF AS THE WOULD-BE EVENT DRAWS NEAR. AT ANY
RATE, WIDESPREAD LIFR IS EXPECTED, WITH A VERY SLOW IMPROVEMENT
ONCE AGAIN OWING TO A LACK OF ANY STRONG MECHANISM TO DISLODGE
THE ENTRENCHED LOW CLOUDS AND COOL TEMPS.
OUTLOOK: RESTRICTIONS MAY NOT CLEAR OUT UNTIL TUESDAY AFTERNOON. AN
UNSETTLED PATTERN CONTINUES THROUGH THE REST OF THE WEEK AS
MULTIPLE STORM SYSTEMS PUSH INTO REGION LIKELY LEADING TO PERIODS
OF ASSOCIATED RESTRICTIONS.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...AR/DEO
NEAR TERM...CAC/PM
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...PM
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