148
FXUS62 KGSP 200555
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1255 AM EST FRI DEC 20 2024
SYNOPSIS
MUCH COOLER CONDITIONS ARE EXPECTED TO FILTER INTO OUR REGION
TO END THE WEEK. A NORTHWEST FLOW SNOW EVENT WILL PRODUCE LIGHT SNOW
ALONG THE TENNESSEE BORDER AREAS FROM LATE FRIDAY THROUGH SATURDAY
MORNING. THE COLDEST DAYS ARE EXPECTED TO BE SUNDAY AND MONDAY THEN
A LITTLE WARMER FOR CHRISTMAS.
NEAR TERM /THROUGH TODAY/
AS OF 938 PM: SURFACE HIGH PRESSURE CENTERED OVER QUEBEC HAS
RESULTED IN A WEDGE-LIKE PATTERN ACROSS THE REGION WITH NORTHEAST
FLOW. WEAK ISENTROPIC ASCENT FROM SOUTHERLY LOW- AND MID-LEVEL FLOW
HAS RESULTED IN A BLOSSOMING DECK OF LOW STRATUS CLOUDS ACROSS MUCH
OF THE AREA. CLOUD COVER WILL CONTINUE OVERNIGHT AND A FEW
SPRINKLES/DRIZZLE WILL BE POSSIBLE AS WELL. SOME PATCHY FOG MAY ALSO
DEVELOP ALONG AND NORTH OF THE I-40 CORRIDOR. TEMPERATURES WILL BE
SOMEWHAT MILD AS CLOUD COVER WILL PRECLUDE MORE EFFICIENT COOLING.
THUS, LOW TEMPERATURES WERE BOOSTED A COUPLE DEGREES WITH LOWS IN
THE MID 30S TO MID 40S.
FRIDAY, THE VIGOROUS SHORTWAVE ASSOCIATED WITH A CLIPPER WILL DIVE
THRU THE OHIO VALLEY, RESULTING IN STRONG UPPER FORCING ACROSS THE
FORECAST AREA. FLOW WILL TURN OUT OF THE WEST, THEN NORTHWEST DURING
THE DAY, SCOURING OUT THE STRATUS. TEMPS ARE EXPECTED TO GET INTO
THE MID 50S WITH HELP FROM DOWNSLOPE WARMING AND CLEARING SKIES.
THIS COMBINED WITH STEEPENING MID-LEVEL LAPSE RATES WITH THE PASSING
SHORTWAVE WILL YIELD SOME SBCAPE EAST OF THE MOUNTAINS. MOST
GUIDANCE AGREES ON ISOLATED TO SCATTERED SHOWERS DEVELOPING IN THE
NC PIEDMONT IN THE AFTN, QUICKLY TRACKING EAST-SOUTHEAST BY EARLY
EVENING. INSTABILITY WILL PROBABLY NOT BE ENOUGH FOR ANY THUNDER,
BUT FORECAST SOUNDINGS SUGGEST CANNOT RULE OUT GRAUPEL/SMALL HAIL IN
THE DEEPEST CONVECTION. MEANWHILE, 850 MB TEMPS WILL PLUMMET ACROSS
THE MOUNTAINS, WITH NW FLOW UPSLOPE SHOWERS RAMPING UP ALONG THE TN
BORDER. SFC TEMPS WILL START OUT ABOVE FREEZING IN THE HIGH TERRAIN,
BUT THE HIGHEST PEAKS COULD SEE SOME ACCUMULATING SNOW BEFORE
SUNSET, ESPECIALLY IN THE SMOKIES WHERE THE COLD AIR WILL ARRIVE
FIRST.
SHORT TERM /TONIGHT THROUGH SUNDAY/
AS OF 210 PM EST THURSDAY: A NORTHWEST FLOW SNOW EVENT WILL BE FULLY
ONGOING ACROSS THE USUAL LOCATIONS FRIDAY NIGHT BEHIND THE DEPARTING
ALBERTA CLIPPER SURFACE LOW. EXPEC SNOW CHANCES TO SLOWLY DIMINISH
OVERNIGHT BUT LINGER INTO SATURDAY MORNING BEFORE ENDING BY
AFTERNOON. ALL ELEMENTS ARE THERE FOR ACCUMULATING SNOWFALL TO
CONTINUE ACROSS MAINLY THE HIGHER ELEVATIONS, BUT SOME LIGHT
ACCUMULATIONS WILL OCCUR IN THE NW TO SE ORIENTED VALLEYS AS WELL.
STORM TOTALS LOOK TO BE 1 TO 4 INCHES WITH LOCALLY HIGHER AMOUNTS
ACROSS THE HIGHER ELEVATIONS. LOWER ELEVATIONS COULD SEE UP TO
AROUND AN INCH. A WINTER WEATHER ADVISORY MAY BE NEEDED BY THE TIME
THE EVENT ARRIVES. VERY GUSTY CONDITIONS ARE ALSO EXPECTED.
OUTSIDE OF THE MOUNTAINS CLOUDS WILL SCATTER OUT FRIDAY EVENING BUT
BREEZY TO WINDY CONDITIONS CONTINUE.
CLEAR SKIES AND LIGHTER WINDS ARE EXPECTED FOR EVERYONE SATURDAY
NIGHT AND SUNDAY. THE COLD AIR BEGINS FILTERING IN FRIDAY NIGHT AND
SATURDAY. LOWS WILL BE AROUND 5 DEGREES BELOW NORMAL WITH HIGHS 5 TO
10 DEGREES BELOW NORMAL. THE COLD AIR MASS FULLY SETTLES IN SATURDAY
NIGHT AND SUNDAY WITH TEMPS 10 TO 15 DEGREES BELOW NORMAL.
LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/
AS OF 150 PM EST THURSDAY: GUIDANCE STILL UNCERTAIN ABOUT THE PRECIP
CHANCES THROUGH THE PERIOD, BUT THEY DO AGREE THAT IF THERE IS
PRECIP, IT SHOULD ALL BE LIQUID. AN UPPER RIDGE STARTS OUT OVER THE
AREA MONDAY, THEN FLATTENS AS A SHORT WAVE PASSES BY TO OUR NORTH ON
TUESDAY. THE RIDGE RETURNS FOR CHRISTMAS DAY AS SHORT WAVES DIG INTO
THE CENTRAL CONUS. THE GFS BRINGS ONE OF THE SHORT WAVES ACROSS THE
AREA EARLY THURSDAY. THE ECMWF DOESN'T PHASE THE SHORT WAVES TAKING
ONE WELL NORTH OF THE AREA CHRISTMAS NIGHT THEN REBUILDING THE RIDGE
THURSDAY AS ANOTHER SHORT WAVE DIVES INTO THE SOUTHERN PLAINS. THE
CANADIAN IS MORE SIMILAR TO THE GFS BUT STRONGER AND FASTER WITH THE
LATE PERIOD SHORT WAVE. AT THE SURFACE, THEY AGREE ON A HIGH
PRESSURE IN CAD CONFIGURATION FOR MONDAY. THE SHORT WAVE PASSING
NORTH OF THE AREA TUESDAY SPLITS THE HIGH WITH A WEAK FRONT DROPPING
TOWARD THE AREA BUT HIGH PRESSURE CENTERED OVER US. THE FRONT STALLS
TO OUR NORTH CHRISTMAS DAY. THEN THE GFS BRINGS MOISTURE AND PRECIP
IN THURSDAY WITH LOW PRESSURE MOVING INTO THE OH VALLEY AND FORMING
ALONG THE CAROLINA COAST. THE CANADIAN SHOWS THIS AS WELL BUT BUT
BRINGS PRECIP IN AS EARLY AS LATE CHRISTMAS EVE AND CONTINUING
THROUGH THURSDAY MORNING. THE ECMWF HOLDS OFF ON ANY SIGNIFICANT
PRECIP UNTIL LATE THURSDAY AT THE EARLIEST. THE GFS AND CANADIAN
ENSEMBLE MEANS ARE ALSO WETTER, BUT WARM ENOUGH FOR ANY PRECIP TO BE
LIQUID. THE PREVIOUS RUN OF THE ECMWF ENSEMBLE MEAN AS ALSO WET BUT
WARM. THAT'S A LOT OF WORDS TO SAY THERE IS QUITE A BIT OF
UNCERTAINTY IN THE FORECAST. THEREFORE, WENT CLOSE TO THE GUIDANCE
BLEND WHICH HAS A DRY MONDAY AND TUESDAY AND CHANCE POPS CHRISTMAS
DAY AND THURSDAY. IT ALSO HAS TEMPS MONDAY WELL BELOW NORMAL WITH A
WARMING TREND THROUGH THE PERIOD WITH TEMPS RISING TO NEAR NORMAL
FOR CHRISTMAS DAY AND ABOVE NORMAL ON THURSDAY. AS MENTIONED ABOVE,
THIS KEEPS ALL PRECIP LIQUID FOR NOW.
AVIATION /06Z FRIDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: MOIST S TO SE FLOW THRU THE OVERNIGHT WILL
HELP KEEP A LOW STRATUS DECK OVER THE AREA WITH A COMBINATION OF
MVFR AND IFR CIG RESTRICTIONS EXPECTED. MOST TERMINALS WILL LIKELY
REMAIN MVFR, BUT A FEW INSTANCES OF IFR ARE LIKELY, ESPECIALLY AT
KHKY WHERE IFR IS EXPECTED TO PREVAIL FOR SEVERAL HRS. MVFR VISBY
FROM PATCHY FOG/DRIZZLE WILL ALSO BE POSSIBLE THRU THE MORNING HRS,
HOWEVER CONFIDENCE IS TOO LOW TO INCLUDE IN THE TAFS. THEREAFTER,
AN ARCTIC COLD FRONT WILL QUICKLY MOVE ACROSS THE AREA TODAY SHIFT-
ING WINDS OUT OF THE NW ALONG WITH RAPIDLY CLEARING CONDITIONS AND
A RETURN TO VFR CONDITIONS. A COUPLE OF SCT SHOWERS WILL BE POSSIBLE
WITH THE FROPA AT KCLT AND KHKY. THIS WAS NOTED WITH PROB30S FOR A
FEW HRS AT BOTH SITES.
OUTLOOK: OTHER THAN A CHANCE OF SNOW ALONG THE TN BORDER FRIDAY PM
THRU SATURDAY AM FROM A REINFORCING COLD FRONT, EXPECT HIGH PRESSURE
AND DRY CONDITIONS TO PERSIST THRU THE WEEKEND. PERIODIC CIG RESTRIC-
TIONS WILL BE POSSIBLE WITH THE FRONTAL PASSAGE.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 1 PM EST
SATURDAY FOR NCZ033-048>052.
SC...NONE.
SYNOPSIS...DEO
NEAR TERM...JPT/TW
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JPT
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