536
FXUS62 KGSP 150559
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1259 AM EST SUN DEC 15 2024
SYNOPSIS
PRECIPITATION WILL DEVELOP TONIGHT AS A WEAK FRONTAL SYSTEM
PASSES TO OUR NORTH. TEMPERATURES WILL LIKELY BE COLD ENOUGH
IN THE NORTHERN MOUNTAINS FOR SOME OF THIS PRECIPITATION TO
FALL AS FREEZING RAIN LEADING TO SOME ICE ACCUMULATION SUNDAY
MORNING. AFTER A CHILLY AND DAMP SUNDAY, MOSTLY DRY AND RELA-
TIVELY WARM WEATHER RETURNS ON MONDAY.
NEAR TERM /THROUGH TODAY/
AS OF 100 AM EST SUNDAY: LAPS/RTMA SURFACE WETBULB TEMP OBSERVATIONS
CONTINUE TO INDICATE THE FAVORABLE LOCATIONS ALONG THE ESCARPMENT
AND NORTHERN MOUNTAINS ARE IN PRIME POSITION FOR FREEZING RAIN AT
THE ONSET AS PRECIP INCHES CLOSER FROM THE WEST. OTHERWISE, THE
FORECAST REMAINS ON TRACK.
MADE SOME MINOR TWEAKS TO OVERNIGHT TEMPERATURES TO RAISE THEM JUST
A TAD IN THE NORTHERN MOUNTAINS BASED ON NEW GUIDANCE AND CURRENT
TRENDS. ADJUSTED POP TRENDS TO ACCOUNT FOR PRECIP MOVING INTO SW NC
MOUNTAINS AT UPDATE TIME. WILL HAVE TO MONITOR THE NW NC PIEDMONT AS
NEW GRIDS ARE SPITTING OUT SOME LIGHT FREEZING RAIN THERE IN THE PRE-
DAWN HOURS BUT NO ACCUMS AT THIS TIME, IT SEEMS ANYTHING THAT MAY
FALL WOULDN'T REALLY HAVE A CHANCE TO ACCRETE BUT IF CAA INCREASED
MORE THAN ANTICIPATED POSSIBLE SOME LIGHT FREEZING RAIN MAY STICK TO
ELEVATED SURFACES.
OTHERWISE, BIG PICTURE-WISE, THE ACTORS ARE IN PLACE FOR A CLASSIC
COLD AIR DAMMING WEDGE TO DEVELOP THIS EVENING. A SPLIT FLOW UPPER
PATTERN HAS A STRONG NRN STREAM RIDGE SUPPORTING A LARGE AND
SPRAWLING SFC HIGH ANCHORED OVER THE ST LAWRENCE REGION LATE THIS
AFTERNOON, ALREADY RIDGING DOWN EAST OF THE MTNS. ALL WE LACK IS LOW
LEVEL MOISTURE RETURN AND PRECIP TO LOCK IN THE WEDGE. THAT PROBABLY
WON'T HAPPEN THROUGH THE BETTER PART OF THE EVENING, BUT WHEN IT
DOES, DEVELOPMENT MAY BE QUICK. ISENTROPIC LIFT WILL STRENGTHEN
THROUGH THE EVENING, FOLLOWED BY THE MOISTURE RETURN IN THE MID/LATE
EVENING, WILL FORCE THE DEVELOPMENT OF LIGHT PRECIP AROUND MIDNIGHT,
FIRST NEAR THE BLUE RIDGE ESCARPMENT AND THEN EXPANDING OUTWARD FROM
THERE. MEANWHILE, THE PRECIP ASSOCIATED WITH THE ACTUAL SFC LOW/COLD
FRONT WILL MOVE IN FROM THE WEST AFTER MIDNIGHT. PRECIP PROBS
INCREASE ACCORDINGLY. THE MAIN ISSUE WILL BE THE SFC TEMPS, WHICH
WILL HAVE THE OPPORTUNITY TO DROP DOWN THROUGH THE 30S WITH THE COLD
ADVECTION IN THE BOUNDARY LAYER, LEADING TO A P-TYPE PROBLEM.
PARTIAL THICKNESSES AND FCST SOUNDINGS LOOK ALL-TOO-TYPICAL, WITH A
PROMINENT WARM NOSE OVER THE TOP OF TRAPPED COLD AIR MAINLY NEAR THE
BLUE RIDGE ESCARPMENT IN NC. THE FCST TREND APPEARS TO BE TOWARD A
STRONGER OR DEEPER WARM NOSE THAT WOULD HAVE ENOUGH ENERGY TO
COMPLETELY MELT FALLING HYDROMETEORS. SO, ALTHOUGH SOME BRIEF SLEET
WILL BE POSSIBLE, OR EVEN LIKELY, THE BULK OF THE PRECIP SHOULD FALL
AS LIQUID, WITH PATCHES OF FREEZING RAIN INDICATED BY THE COLD SFC
TEMPS. IN THESE SITUATIONS, WE USUALLY GET SOME COLD AIR TRAPPED ALL
THE WAY DOWN INTO THE UPPER FRENCH BROAD VALLEY. FORTUNATELY, THE
AMOUNTS OF PRECIP LOOK LOW ENOUGH TO KEEP THE ICE ACCUM POTENTIAL
BELOW WARNING CRITERIA. THINK THE BEST COURSE OF ACTION WILL BE TO
EXPAND THE ADVISORY DOWN INTO TRANSYLVANIA/HENDERSON COUNTIES AND
THE MOUNTAINOUS WESTERN PARTS OF POLK/RUTHERFORD, BECAUSE OF THE
LIKELIHOOD OF SOME ICY PATCHES EARLY SUNDAY MORNING. THE REST OF THE
ADVISORY AREA WILL REMAIN UNCHANGED, BUT LATER DEVELOPMENTS IN THE
TEMPERATURE FORECAST MAY DICTATE ANOTHER EXPANSION. SUNDAY LOOKS
LIKE A TYPICAL WINTER WEDGE DAY, WITH TEMPS STUBBORNLY REMAINING IN
THE 40S OVER MOST OF THE REGION, PROBABLY 10-15 DEGREES BELOW NORMAL.
SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/
AS OF 200 AM SAT: THE IMPACT OF WINTRY PRECIP IN THE NC MOUNTAINS
AND FOOTHILLS WILL DECREASE ONCE SFC TEMPS RISE ABOVE FREEZING SUN
MORNING, AS SUCH TEMPS WILL PRECLUDE FREEZING RAIN. ONGOING STRONG
WAA WILL PROMOTE SFC WARMING ALTHOUGH THE ESPECIALLY STRONG DAMMING
HIGH SHOULD PROVE FAIRLY TOUGH TO ERODE; SHORTWAVE TROUGH PASSING BY
TO OUR NORTH HOWEVER MAY HELP EROSION VIA PRECEDING DIFFLUENCE. THE
12KM AND 3KM NAMS ALONG WITH THE SIMILARLY CONSTRUCTED HIRES
ARW ARE THE MOST STUBBORN IN HOLDING ONTO COLD AIR, ALLOWING
WET-BULBS TO FALL BELOW FREEZING EARLY ACROSS A BROAD PORTION OF
OUR I-40 CORRIDOR AND NOT WARMING THEM UNTIL EARLY AFTERNOON. CAN'T
COMPLETELY DISCOUNT THAT IDEA ON ACCOUNT OF THE SFC HIGH, BUT THINK
IN TERMS OF AREAL EXTENT IT MAY VERIFY CLOSER TO THE HRRR, SO OUR
FORECAST TEMPS/WET-BULBS LOOK MUCH MORE LIKE THAT MODEL'S DEPICTION
IN THE NORTHERN ESCARPMENT AREA, AND CLOSE TO THE 25TH PERCENTILE OF
THE NBM. A COLD, DAMP DAY FOR THE MAJORITY OF THE AREA. CURRENTLY
WE EXPECT TEMPS AT OR BELOW FREEZING TO LINGER THE NORTHERN BLUE
RIDGE ESCARPMENT UNTIL LATE MORNING, PERHAPS AS LATE AS NOON OR SO.
ANOTHER FACTOR TO CONSIDER IS THAT THE PRECIP RATES INITIALLY WILL
BE PRETTY LIGHT BUT MOST MODELS TICK THEM UPWARD IN THE 7-10 AM
TIMEFRAME; IF AIR TEMPS HAVE NOT ALREADY COOLED TO WET-BULB TEMPS,
THERE MIGHT BE ONE LAST CHANCE TO DO SO IN THAT PERIOD, SO TO SPEAK.
PROFILES IN THAT PERIOD SUGGEST PRIMARILY RAIN WHERE SFC TEMPS
ARE ABOVE FREEZING. HOWEVER, SAMPLING HREF PROFILES FROM VARIOUS
SPOTS IN THE NORTHERN MOUNTAINS, THE WARM NOSE IS SMALL AND VARIABLE
ENOUGH THAT IT SEEMS QUITE LIKELY SOME SNOW AND SLEET WILL MIX IN AT
TIMES, ALTHOUGH ACCUMULATIONS OF ICE APPEAR MUCH MORE APPRECIABLE;
WHERE TEMPS SUPPORT ONLY RAIN ACCUMULATION SNOW/SLEET CERTAINLY
COULD MIX IN BUT NOT LIKELY PRODUCING ACCUMULATION.
DYNAMIC LIFT STILL LOOKS BEST EARLY IN THE MORNING ALTHOUGH THERE
MAY BE A SECONDARY SHOT IN THE AFTERNOON WITH TROUGH AXIS PASSING,
AND DEEPER MOISTURE ARRIVING AROUND THEN ALSO. WARM ADVECTION
WILL SLOWLY WEAKEN BUT NOT LIKELY TO CEASE THROUGH EARLY MONDAY;
CLOUD COVER WILL LINGER THRU THE NIGHT, BUT POPS WILL GRADUALLY
DIMINISH AS WINDS VEER IN THE LOW LEVELS AND WITH RIDGING DEVELOPING
ALOFT. TEMPS LIKELY WILL CONTINUE TO TREND SLIGHTLY WARMER THRU
AROUND PEAK HEATING SUNDAY AND THEN REMAIN NEARLY STEADY UNTIL
MONDAY MORNING; ANY REMAINING PRECIP WILL BE ALL LIQUID. THE
SFC HIGH WILL BE CENTERED OFFSHORE BY MONDAY, BUT A PORTION OF
IT STILL WILL EXTEND INLAND OVER NC/SC/GA UNDER LOW AMPLITUDE
RIDGE. WITHOUT SUPPORTING CONFLUENCE ALOFT AND WITH AIRMASS LIKELY
WILL HAVE MODIFIED, CAD SHOULD BE HISTORY AND TEMPS REBOUND 15-20
DEGREES MONDAY COMPARED TO SUNDAY, THUS A FEW ABOVE NORMAL.
LONG TERM /TUESDAY THROUGH SATURDAY/
AS OF 245 AM SAT: A SFC CYCLONE WILL STRENGTHEN NORTH OF THE GREAT
LAKES MONDAY NIGHT IN CONJUNCTION WITH A SYNOPTIC SCALE, NEGATIVELY
TILTED TROUGH. THE TRAILING COLD FRONT WILL CROSS THE LOWER OHIO
VALLEY AND REACH THE SOUTHERN APPALACHIANS EARLY TUESDAY MORNING.
JET STREAK IN THE EXIT REGION OF THE TROUGH MAY OFFER WEAK DYNAMIC
SUPPORT IN OUR GENERAL VICINITY, BUT MOST OF THE BETTER FORCING WILL
BE FAR OFF TO OUR NORTH. THE FRONT OVERALL HAS A LESS IMPRESSIVE
DEPICTION THAN IT DID YESTERDAY AT THIS TIME, AND MODEL QPF RESPONSE
IS TAPERING OFF AS IT REACHES THE MOUNTAINS, SO WHILE WE FEATURE
DECENT POPS ALONG THE TN BORDER THE PIEDMONT JUST GETS A 20-30%
CHANCE. MINIMAL IMPACT AS TEMPS WILL BE COMFORTABLY ABOVE FREEZING.
THE FRONT PIVOTS ACROSS THE UPPER SOUTHERN STATES TUESDAY, NOT
LIKELY GETTING FAR ENOUGH SOUTH TO BRING AIRMASS CHANGE TO OUR
CWA. WITH DIMINISHING CLOUD COVER AND WESTERLY DOWNSLOPE WINDS
WE STILL EXPECT TEMPS WILL TOP OUT IN THE MID-UPPER 60S FOR THE
VALLEYS AND PIEDMONT. THE FRONT WILL BE SUBSEQUENTLY REACTIVATED BY
A SHORTWAVE MOVING OUT OF TEXAS WHICH PHASES WITH A DEEPER TROUGH
DIGGING ACROSS THE CENTRAL CONUS WEDNESDAY. THERE IS SPREAD ON
WHERE THE REACTIVATION OCCURS BUT E.G. THE 14/00Z ECMWF SUGGESTS
IT WOULD BE IN POSITION TO BRING PRECIP BACK TO OUR AREA TUESDAY
NIGHT. TEMPS WILL REMAIN ABOVE NORMAL WEDNESDAY.
MODELS HAVE COME INTO SOMEWHAT BETTER AGREEMENT ON THE HANDLING OF
THE TROUGH, MOSTLY SHOWING THE PHASED TROUGH INITIATING CYCLOGENESIS
NEAR THE OZARKS AND THE INCIPIENT LOW TRACKING GENERALLY TOWARD
PENNSYLVANIA. THE TROUGH AXIS AND COLD FRONT REACH THE SOUTHERN
APPALACHIANS SOMETIME BETWEEN LATE WEDNESDAY AND THURSDAY MORNING.
SBCAPE MAY DEVELOP AHEAD OF THESE FEATURES, AND SMALL THUNDER
CHANCES ARE INCLUDED IN SOME OF OUR SE ZONES WED NIGHT. CAN'T
RULE OUT A SEVERE THREAT ALTHOUGH CONFIDENCE VERY LOW ON THE
PATTERN/TIMING. A TRANSITION TO SNOW WOULD APPEAR POSSIBLE ON
THE BACK SIDE OF THE SYSTEM, AT LEAST FOR THE NW FLOW AREAS. TEMPS
RETURN TO NEAR NORMAL THURSDAY AND THURSDAY NIGHT.
AVIATION /06Z SUNDAY THROUGH THURSDAY/
AT KCLT AND ELSEWHERE: CONDITIONS ARE DETERIORATING QUICKLY AS THE
MVFR LOW CLOUD DECK SPREADS ACROSS THE AREA AND LOCKS IN FOR MUCH
OF THE PERIOD. EXPECT SOME TERMINALS TO GRADUALLY LOWER TO IFR
BY DAYBREAK AND REMAIN THAT WAY THROUGH THE DAY, ESPECIALLY AT
THE UPSTATE TAF SITES AND KHKY/KAVL. KCLT WILL REMAIN LOW-END
MVFR THROUGH MOST OF THE DAY, BEFORE DROPPING TO IFR AFTER
00Z MONDAY. SCATTERED SHOWERS AND DRIZZLE WILL MOVE ACROSS
THE TERMINALS JUST BEFORE DAYBREAK AND REMAIN THAT WAY THROUGH
SUNSET BEFORE COVERAGE SLOWLY LESSENS. THERE ARE SOME HINTS THAT
TEMPERATURES COULD COOL ENOUGH FOR A BRIEF PERIOD OF FREEZING
RAIN AT KAVL AND INCLUDED THIS IN A TEMPO AROUND OR JUST BEFORE
DAYBREAK, BUT PRECIP WILL QUICKLY RETURN TO ALL LIQUID SOON AFTER
SUNRISE THIS MORNING. KCLT WILL STRUGGLE TO EEK OUT A FEW SHOWERS
UNTIL LATER IN THE AFTERNOON, BUT STILL KEPT A VCSH MENTION AS
A FEW PATCHES OF PRECIP SHOULD BREAK CONTAINMENT AND CROSSOVER
THE TERMINAL. WINDS WILL MAINTAIN A NORTHEASTERLY COMPONENT AT
ALL TAF SITES WITH LOW-END GUSTS THROUGH DAYBREAK AS THE PRESSURE
GRADIENT STAYS TIGHT AS THE DOME OF COLD AIR LOCKS IN. GUSTS WILL
GRADUALLY DROP OFF DURING THE DAY AND PREVAILING WINDS WILL DROP
UNDER 10 KTS AT ALL SITES BY THIS EVENING. KAVL WILL CONTINUE TO
TOGGLE OUT OF THE SOUTHEAST THROUGH THE FORECAST PERIOD.
OUTLOOK: RESTRICTIONS WILL CONTINUE MONDAY MORNING BUT EXPECT
GRADUAL LIFTING AS THE DAMMING CLEARS DURING THE DAY. 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...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ033-049-
050-053-064-065-501-503-505-507-509.
SC...NONE.
SYNOPSIS...JPT
NEAR TERM...CAC/PM/TDP
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...CAC
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