996
FXUS62 KGSP 151930
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
230 PM EST SUN DEC 15 2024
SYNOPSIS
CHILLY, CLOUDY, AND RAINY WEATHER CONTINUES INTO TONIGHT BEFORE
TAPERING OFF AROUND DAYBREAK MONDAY. TEMPERATURES WILL BE ON A
WARMING THROUGH THE FIRST HALF OF THE WORKWEEK, WITH RAIN CHANCES
BRIEFLY RETURNING TO THE MOUNTAINS MONDAY NIGHT AND TO ALL LOCATIONS
BY WEDNESDAY. DRIER AND COOLER CONDITIONS CAN BE EXPECTED THURSDAY
INTO THE WEEKEND.
NEAR TERM /THROUGH MONDAY/
AS OF 149 PM EST SUNDAY: TEMPS HAVE WARMED ABOVE FREEZING ACROSS
AVERY COUNTY NC, SO THE PRECIP SHOULD BE ALL RAIN FROM HERE ON
OUT. AND RAIN IT WILL OVER MOST PLACES AS A LARGE AREA OF LIGHT
PRECIP WAS MAKING STEADY EASTWARD PROGRESS AHEAD OF A SHORT
WAVE. PRECIP PROBS WILL BE ADJUSTED ACCORDINGLY, MOST LIKELY
UPWARD OVER THE WESTERN PIEDMONT OF NC. MEANWHILE, A CLASSIC COLD
AIR DAMMING WEDGE WILL PERSIST THANKS TO A LARGE 1050MB SFC HIGH
ANCHORED OVER THE ST LAWRENCE VALLEY. THAT WILL KEEP TEMPS DOWN
ABOUT 10-15 DEGREES BELOW NORMAL.
THE COLD AIR DAMMING SETUP WILL DEVOLVE TONIGHT AS AN UPPER LOW
MOVES FROM THE GREAT LAKES TO THE HUDSON VALLEY, CUTTING US OFF
FROM THE PARENT HIGH OVER NEW ENGLAND AND PUSHING IT OFFSHORE
OF THE CANADIAN MARITIMES. SUPPORT WILL WANE SLOWLY THOUGH,
WITH WEAK WARM ADVECTION AND UPGLIDE OVER TOP OF THE OLD WEDGE
PERSISTING INTO THE EARLY MORNING HOURS MONDAY. THUS, PRECIP
CHANCES SLOWLY BACK OFF OVER THE DAMMING REGION WHILE LOW CLOUDS
ARE MAINTAINED. THE LAST OF THE PRECIP SHOULD MOVE OUT OF THE NW
PIEDMONT AROUND DAYBREAK. EXPECT A LOW DIURNAL RANGE WITH TEMPS
DROPPING OFF AT BEST 3-5 DEGREES FROM WHAT THEY ARE LATE THIS
AFTERNOON, AND FORTUNATELY ALL ABOVE FREEZING.
THE PROBLEM FOR MONDAY IS THAT...WHILE WE NO LONGER HAVE SUPPORT TO
MAINTAIN THE WEDGE, WE ALSO LACK A MECHANISM TO REALLY DESTROY THE
REMNANT COOL POOL EAST OF THE MTNS. A FLAT UPPER RIDGE WILL MOVE
OVERHEAD AND BRING THE UPPER FLOW AROUND TO MORE WSW, WHILE THE
FLOW AT 850MB BECOMES SW. AS A RESULT, WE WON'T GET ANY MEANINGFUL
DOWNSLOPE EAST OF THE MTNS AND NO COLD ADVECTION ALOFT. THE FLOW
MIGHT NOT BE STRONG ENOUGH FOR TURBULENT MIXING AT THE TOP OF THE
INVERSION LAYER, SO WE MIGHT HAVE TO MIX OUT THE LINGERING LOW
CLOUDS FROM THE EDGES, WHICH IS A DIFFICULT PROSPECT SO CLOSE TO
THE SOLSTICE. HAVE MY DOUBTS ABOUT THE HIGH TEMPS GETTING OUT OF
THE 50S EAST OF THE MTNS, OR THE UPPER 40S OVER THE NRN FOOTHILLS,
SO WE UNDERCUT THE GUIDANCE FOR THE HIGH TEMPS. NOTE THERE MAY BE
A TIGHT GRADIENT WHERE THE CLOUDY/CLEAR BOUNDARY SETS UP IN THE
AFTERNOON, WHICH WOULD AFFECT MAINLY THE SOUTHERN CLT METRO AREA
TO THE LOWER PIEDMONT.
SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/
AS OF 130 PM EST SUNDAY...
KEY MESSAGES:
1) RAIN WILL BE CONFINED TO THE WESTERN NORTH CAROLINA MOUNTAINS
MONDAY NIGHT INTO TUESDAY MORNING, WITH COLD AIR DAMMING ERODING BY
TUESDAY AFTERNOON
2) MUCH WARMER AND WELL ABOVE NORMAL TEMPERATURES EXPECTED THROUGH
THE SHORT TERM
3) RAIN CHANCES RETURN AREA-WIDE WEDNESDAY INTO WEDNESDAY NIGHT
A COLD FRONT WILL TRACK OUT OF THE WEST MONDAY NIGHT BEFORE PUSHING
INTO THE WESTERN NORTH CAROLINA MOUNTAINS BY DAYBREAK TUESDAY. CLOUD
COVER IN PLACE AHEAD OF THE FRONT WILL LIMIT RADIATIONAL COOLING,
LEADING TO LOWS ~15-20 DEGREES ABOVE NORMAL MONDAY NIGHT. THE FRONT
LOOKS TO PETER OUT WHILE PUSHING EAST SO RAIN CHANCES WILL BE
CONFINED TO THE NORTH CAROLINA MOUNTAINS MONDAY NIGHT INTO TUESDAY.
WITH THE FRONT EXPECTED TO FALL APART OVER THE MOUNTAINS, WINDS WILL
TOGGLE NW ACROSS THE MOUNTAINS BUT WILL REMAIN SW EAST OF THE
MOUNTAINS. THIS NW DOWNSLOPE FLOW WILL GRADUALLY ERODE THE WEDGE BY
TUESDAY AFTERNOON, LEADING TO MUCH WARMER HIGHS (~15 DEGREES ABOVE
NORMAL). TEMPS WILL CLIMB INTO THE MID TO UPPER 60S EAST OF THE
MOUNTAINS AND IN THE MOUNTAIN VALLEYS ON TUESDAY, WITH TEMPS ACROSS
THE HIGHER ELEVATIONS RANGING FROM THE LOWER TO UPPER 50S.
RAIN CHANCES RETURN FOR THE ENTIRE FORECAST AREA THE REST OF THE
SHORT TERM FORECAST PERIOD AS ANOTHER MORE POTENT COLD FRONT
APPROACHES OUT OF THE WEST TUESDAY NIGHT INTO WEDNESDAY, TRACKING
ACROSS THE FORECAST AREA WEDNESDAY EVENING. HAVE THE HIGHEST POPS
PAINTED ACROSS THE MOUNTAINS AND THE NORTHERN NC FOOTHILLS/PIEDMONT
PER THE LATEST GLOBAL MODEL GUIDANCE. TEMPERATURES WILL ONCE AGAIN
END UP WELL ABOVE NORMAL TUESDAY NIGHT (~20 DEGREES) THANKS TO
INCREASING CLOUD COVER. STRONG SW'LY FLOW AHEAD OF THE FRONT WILL
LEAD TO ANOTHER VERY WARM AFTERNOON ON WEDNESDAY, WITH HIGHS ENDING
UP A DEGREE OR TWO WARMER THAN TUESDAY. RAIN CHANCES WILL GRADUALLY
TAPER OFF WEDNESDAY NIGHT BEHIND THE FRONT. LOWS WEDNESDAY NIGHT
WILL BE NOTICEABLY COOLER THANKS TO CAA FILTERING INTO THE REGION
AND GRADUALLY DECREASING CLOUD COVER. HOWEVER, TEMPS WILL STILL END
UP ~10-12 DEGREES ABOVE NORMAL.
LONG TERM /THURSDAY THROUGH SUNDAY/
AS OF 200 PM EST SUNDAY...
KEY MESSAGES:
1) DRIER CONDITIONS EXPECTED THROUGH THE LONG TERM
2) COOLING TREND STARTS THURSDAY WITH BELOW NORMAL TEMPERATURES
RETURNING BY THE WEEKEND
3) PERIODIC NW FLOW SNOW SHOWERS ARE POSSIBLE ALONG THE NC/TN BORDER
FRIDAY INTO SATURDAY
SFC HIGH PRESSURE BUILDS INTO THE WESTERN CAROLINAS AND NORTHEAST
GEORGIA THURSDAY INTO FRIDAY BEFORE A MOSTLY DRY COLD FRONT TRACKS
ACROSS THE REGION LATE FRIDAY. THERE COULD BE ENOUGH MOISTURE
ALONG/BEHIND THE FRONT TO ALLOW FOR SOME LIGHT AND PERIODIC NW FLOW
SNOW SHOWERS TO DEVELOP FRIDAY EVENING INTO SATURDAY MORNING.
HOWEVER, CONFIDENCE ON WHETHER THERE WILL BE ENOUGH MOISTURE REMAINS
LOW AT THIS TIME. DID NOT END UP WITH ANY SNOW ACCUMS ALONG THE
NC/TN BORDER THIS FORECAST CYCLE. DRY SFC HIGH PRESSURE RETURNS
BEHIND THE DEPARTING FRONT SATURDAY INTO SUNDAY. TEMPS WILL DEPICT A
COOLING TREND THROUGH THE LONG TERM FORECAST PERIOD, WITH BELOW
NORMAL TEMPS RETURNING BY THE WEEKEND.
AVIATION /20Z SUNDAY THROUGH FRIDAY/
AT KCLT AND ELSEWHERE: WITHOUT THE LIGHT PRECIP TO LOCK IN THE EDGES
OF THE WEDGE, THE SOUTHERN PIEDMONT HAS STARTED TO BREAK OUT OF
THE LOW STRATUS, THUS KCLT HAS GONE VFR. THIS MAY NOT BE MERELY A
TEMPORARY OR BRIEF IMPROVEMENT, AS WITHOUT THE LIGHT PRECIP MOVING
BACK IN, KCLT WILL PROBABLY BE IN AND OUT OF AN MVFR-LEVEL STRATOCU
CEILING WHILE THE IFR LURKS WEST OF THE METRO AREA FOR THE REST
OF THE AFTERNOON. WITH THE CEILING RESTRICTION BEING ESSENTIALLY
A COIN FLIP, WILL OPT FOR THE VFR PREVAILING/MVFR TEMPO PLAN. ALL
OTHER TERMINALS WILL MOSTLY BE FLIPPING BETWEEN IFR AND OCCASIONAL
LIFR CEILING WITH A LARGER PATCH OF LIGHT PRECIP MOVING IN FROM
THE WEST. WIND SHOULD BE MOSTLY NE THROUGH THE AFTERNOON. ONCE
THE SUN SETS, ONGOING LIGHT UPSLOPE/UPGLIDE FLOW SHOULD BRING THE
LOW CLOUDS BACK DOWN AGAIN TO IFR OR LIFR AT ALL TERMINALS FOR THE
NIGHT. ONLY SLOW IMPROVEMENT IS EXPECTED ON MONDAY AS WE LACK A GOOD
MECHANISM TO REMOVE THE CLOUDS AND THE REMNANT COOL POOL. THUS,
ONLY KCLT GETS A REPRIEVE OF SORTS BECAUSE OF THE LONGER FORECAST
VALID PERIOD AND BEING CLOSER TO THE WEDGE BOUNDARY.
OUTLOOK: RESTRICTIONS MAY CONTINUE THROUGH MONDAY NIGHT, BUT SHOULD
CLEAR OUT TUESDAY MORNING. 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
NEAR TERM...PM
SHORT TERM...AR
LONG TERM...AR
AVIATION...PM
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