581
FXUS62 KGSP 152354
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
654 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 600 PM EST SUNDAY: PATCHY DRIZZLE IN PLACE ACROSS THE
WESTERN 2/3 OF THE FORECAST AREA BENEATH A SHORTWAVE ALOFT, WITH
ONLY LIGHT ACCUMULATIONS EXPECTED. CLASSICAL COLD AIR DAMMING
REMAINS IN PLACE ON THE FRINGE OF A SURFACE LOW CENTERED JUST OFF
THE MAINE COASTLINE...HAVING ALREADY BEEN NUDGED A LITTLE EASTWARD
BY THE SHORTWAVE.
THIS TREND SHOULD CONTINUE OVERNIGHT AS A COMPACT UPPER LOW OVER
LAKE ERIE OPENS INTO A SHARP UPPER WAVE AND DRIVES THE SURFACE HIGH
FARTHER OFFSHORE, CUTTING OFF SYNOPTIC SUPPORT FOR THE CAD WEDGE.
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 WERE 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 /00Z MONDAY THROUGH FRIDAY/
AT KCLT AND ELSEWHERE: SETTLING INTO A DREARY NIGHT ACROSS THE
WESTERN CAROLINAS, WITH LINGERING COLD AIR DAMMING IN PLACE.
CLT IS TEETERING ON THE EDGE OF AN MVFR RESTRICTION, AND IS
EXPECTED TO DROP SHORTLY FROM ITS VFR STATE THE LAST FEW HOURS.
THIS PROCESS SHOULD BE HASTENED BY LIGHT DRIZZLE SPREADING ACROSS
THE PIEDMONT FROM THE WEST...AND ONCE THIS MVFR CEILING DEVELOPS,
IT SHOULD STEADILY DROP TO IFR THROUGH MIDNIGHT. THE OTHER TAF
PIEDMONT/UPSTATE TERMINALS WILL FOLLOW A SIMILAR PROGRESSION, MORE
OR LESS...EXCEPT THAT THEY'RE ALREADY MVFR OR IFR, AND ALREADY
EXPERIENCING DRIZZLE. MOST SITES ACROSS THE AREA CAN EXPECT IFR
TO LIFR CEILINGS THROUGH THE OVERNIGHT, ACCOMPANIED BY AT LEAST
PATCHY DENSE FOG, ESPECIALLY ACROSS THE MOUNTAINS AND FOOTHILLS.
BY MONDAY MORNING, THERE WILL BE NOTHING REALLY LOCKING CAD IN
PLACE, BUT ALSO NOTHING OF NOTE TO SCOUR IT OUT - SO IMPROVEMENT
IS EXPECTED...BUT VERY SLOWLY. AS EXPECTED, GUIDANCE IS GRADUALLY
SLOWING ITS IMPROVEMENT TREND, WITH MOST SITES SEEING, AT BEST,
A QUICK FEW HOURS OF MVFR DURING THE AFTERNOON TOMORROW, FOLLOWED
BY A RETURN TO IFR TOMORROW EVENING/NIGHT. KAND IS THE EXCEPTION -
BEING FARTHER SOUTH AND THUS ON THE FRINGE OF THE "WEDGE" MAY GIVE
IT THE OPPORTUNITY TO SCATTER OUT TO MVFR EARLIER, AND FOR LONGER.
AS KCLT IS FARTHER EAST THAN THE OTHER SITES, IT MAY ALSO STAND TO
BENEFIT FROM BEING NEAR THE EDGE OF THE CAD LAYER, BUT GUIDANCE
HAS TRENDED AWAY FROM THIS IDEA THIS EVENING, AND HAS STARTED TO
FAVOR A MORE PESSIMISTIC CEILING FORECAST FOR TOMORROW AFTERNOON.
UNCERTAINTY IS HIGH BEYOND DAYBREAK, HOWEVER, FOR ALL THE TAF SITES.
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...MPR/PM
SHORT TERM...AR
LONG TERM...AR
AVIATION...MPR
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