105
FXUS62 KGSP 201507
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1007 AM EST FRI DEC 20 2024
SYNOPSIS
MUCH COOLER TEMPERATURES WILL FILTER INTO OUR REGION TODAY. A
NORTHWEST FLOW OF MOISTURE WILL PRODUCE LIGHT SNOW ALONG
THE TENNESSEE BORDER AREAS FROM LATE TODAY THROUGH SATURDAY
MORNING. THE COLDEST DAYS ARE EXPECTED TO BE SUNDAY AND MONDAY AS
HIGH PRESSURE TAKES OVER. HOWEVER, TEMPERATURES SHOULD WARM UP A
BIT FOR CHRISTMAS.
NEAR TERM /THROUGH TONIGHT/
AS OF 1005 AM EST FRIDAY: THE EARLIER SHOWERS HAVE MOVED EAST OF THE
AREA. LOW CLOUDS ARE TAKING LONGER TO DISSIPATE THAN PREVIOUSLY
EXPECTED. SHOULD STILL SEE EROSION TAKING PLACE OVER THE WESTERN
UPSTATE AND NE GA AND IN THE LEE OF THE BLUE RIDGE. THEY MAY NOT
COMPLETELY GO AWAY OVER THE I-77 CORRIDOR. DESPITE THE SLOWER
EROSION, TEMPS LOOK ON TRACK, SO ONLY A MINOR ADJUSTMENT THERE.
LATEST CAM GUIDANCE FAVORS AREAS EAST OF OUR CWA FOR ANY HIGHLY
REFLECTIVE CONVECTION AND KEEPS THE MOUNTAIN SNOW SHOWER TIMING
GENERALLY AS FORECAST. THEREFORE, THIS PART OF THE FORECAST STILL ON
TRACK AS WELL.
OTHERWISE, A FAIRLY POTENT UPPER TROF/SHORTWAVE WILL TRANSLATE
OVER OUR AREA TODAY WITH THE TROF AXIS MOVING OFF THE ATLANTIC
COAST BY THE END OF THE PERIOD EARLY SAT. AT THE SFC, WHAT'S
LEFT OF A WEAK WEDGE PATTERN WILL DISSIPATE THIS MORNING AS A
FAST-MOVING CLIPPER LOW TRACKS OVER THE OHIO RIVER VALLEY AND
PUSHES A COLD FRONT THRU OUR AREA LATE THIS MORNING/EARLY THIS
AFTERNOON. THIS WILL CAUSE THE LOW-LVL FLOW TO TURN OUT OF THE
WEST AND THEN NW THIS AFTN, SCOURING OUT ANY LINGERING STRATUS
OUTSIDE THE MTNS. TEMPERATURES ARE EXPECTED TO REACH THE MID
50S WITH HELP FROM DOWNSLOPE WARMING AND CLEARING SKIES. THIS
COMBINED WITH STEEPENING MID-LEVEL LAPSE RATES FROM THE PASSING
OF THE UPPER SHORTWAVE WILL LIKELY YIELD SOME SFC-BASED CAPE OUT-
SIDE OF THE MTNS. MOST OF THE NEAR-TERM GUIDANCE CONTINUES TO
GENERATE SOME ISOLATED TO SCT SHOWERS OVER THE NC PIEDMONT THIS
AFTERNOON, QUICKLY MOVING EAST OF OUR CWA BY THE EARLY EVENING.
INSTABILITY WILL LIKELY NOT BE ENOUGH FOR ANY THUNDER, BUT I WOULD
NOT RULE OUT SOME GRAUPEL/SMALL HAIL IN THE DEEPEST CONVECTION.
MEANWHILE, 850MB TEMPS WILL PLUMMET ACROSS THE MTNS, WITH NW FLOW
SNOW SHOWERS RAMPING UP ALONG THE NC/TN BORDER. SFC TEMPS WILL
START OUT ABOVE FREEZING OVER THE HIGHER TERRAIN, BUT THE HIGHEST
PEAKS COULD SEE SOME ACCUMULATING SNOW BEFORE SUNSET, ESPECIALLY
IN THE SMOKIES WHERE THE COLD AIR WILL ARRIVE FIRST. AFTER THAT,
I EXPECT THE NW FLOW SNOW TO CONTINUE WELL INTO SAT MORNING, AL-
THOUGH WE'RE NOT EXPECTING MUCH AFTER ROUGHLY 12Z SAT. THE LATEST
STORM TOTAL SNOW ACCUMS ARE STILL MINIMAL ONCE YOU GET AWAY FROM
THE NC/TN BORDER, BUT WE DO HAVE ADVISORY CRITERIA OVER THAT AREA.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
AS OF 310 AM EST FRIDAY: WE SHOULD BE ON THE BACK END OF A NW FLOW
SNOW EVENT AT DAYBREAK ON SATURDAY. MODEL GUIDANCE IS CONSISTENT
IN SHOWING A GRADUAL DECLINE IN THE LOW LEVEL MOISTURE THROUGH
MIDDAY. ALTHOUGH THE MOISTURE LOOKS SHALLOW, THE AIR MASS SHOULD BE
COLD ENOUGH SUCH THAT UPSLOPE PARCELS SHOULD GET LIFTED JUST ENOUGH
TO KEEP ICE NUCLEI ACTIVE, THUS WE CONTINUE TO FEATURE LIGHT SHOW
SHOWERS ON THE TN BORDER RATHER THAN A FREEZING DRIZZLE, BUT WHERE
PRECIP DOESN'T OCCUR THERE COULD BE RIME ICING JUST AS EASILY. AT
ANY RATE, THE PRECIP ENDS BY 18Z SATURDAY, BUT CLOUDS LINGER IN
THE WESTERLY UPSLOPE ZONES. MEANWHILE, EAST OF THE MTNS, EXPECT
A SUNNY AND COOL DAY WITH DOWNSLOPE FLOW HELPING TO OFFSET THE
COLD ADVECTION, KEEPING TEMPS ABOUT FIVE UNDER NORMAL. WE SHOULD
REMAIN IN A GENERAL WNW FLOW ALOFT THROUGH SATURDAY NIGHT AND
SUNDAY. EVENTUALLY, A NORTHERN STREAM UPPER RIDGE WILL MOVE A SFC
HIGH ACROSS SOUTHEASTERN CANADA AND THE LOWER GREAT LAKES. THIS SFC
HIGH WILL RIDGE DOWN ACROSS OUR REGION ON SUNDAY AND SUNDAY NIGHT,
TAKING ON A WEDGE-LIKE CONFIGURATION BY DAYBREAK MONDAY. TEMPS WILL
BE SEASONALLY COLD AND ON THE ORDER OF TEN DEGREES BELOW NORMAL,
BUT THE AIR MASS WILL ALSO BE VERY DRY.
LONG TERM /MONDAY THROUGH THURSDAY/
AS OF 251 AM EST FRIDAY: A WEDGE-LIKE SCENARIO IS DEPICTED BY
MODEL GUIDANCE ON MONDAY, WITH A BROAD UPPER RIDGE AXIS TO OUR
WEST SUPPORTING A SFC HIGH CENTER OVER UPSTATE NY/NORTHERN NEW
ENGLAND TO BEGIN THE DAY, THAT RIDGES DOWN THE EAST SIDE OF THE
MTNS THRU THE DAY. EXPECT A MOSTLY SUNNY AND COOL WINTER DAY WITH
TEMPS AROUND TEN DEGREES BELOW NORMAL. HOWEVER, THE NRN STREAM
REMAINS PROGRESSIVE AND THE NEXT SYSTEM QUICKLY PUSHES WHAT WOULD
BE A PARENT HIGH OFFSHORE MONDAY EVENING, LEAVING BEHIND A WEAK
HIGH PRESSURE CENTER OVER THE SRN APPALACHIANS MONDAY NIGHT. THIS
HIGH FINDS MORE SUPPORT IN THE MID/UPPER RIDGE AXIS THAT BUILDS
OVER THE SOUTHEAST/TN VALLEY REGIONS IN RESPONSE TO THE NEXT UPPER
TROF DIGGING DOWN ACROSS THE SRN PLAINS ON TUESDAY. TEMPS SHOULD
REBOUND CLOSE TO NORMAL. A QUICK TRANSITION TAKES PLACE AS THE
BUILDING UPPER RIDGE INTERCEPTS RELATIVELY WEAK HIGH PRESSURE
OVER EASTERN CANADA THAT ESSENTIALLY INCORPORATES THE OLD HIGH
OVER OUR REGION, WHILE WARM ADVECTION AND MOISTURE ADVECTION
DEVELOPS FROM THE GULF/ATLANTIC TOWARD THE WESTERN CAROLINAS
TUESDAY NIGHT. ISENTROPIC LIFT SHOULD BE ABLE TO DEVELOP SOME
LIGHT PRECIP ACROSS THE REGION WITH THE IMPROVING MOISTURE EARLY
WEDNESDAY MORNING. FOR NOW, FCST SOUNDINGS AND SFC TEMPS SUGGEST
THAT ANY PRECIP THAT REACHES THE GROUND IS LIKELY TO STAY ALL RAIN
BECAUSE OF THE WARM ADVECTION KEEPING A DEEP BOUNDARY LAYER ABOVE
32F. OF THE MODELS, THE GFS IS THE FASTEST WITH THIS DEVELOPMENT,
BUT THERE IS AT BEST LUKEWARM SUPPORT IN THE GEFS ENSEMBLE, SO
PRECIP CHANCES WILL BE KEPT LOW FOR NOW. BEYOND CHRISTMAS DAY,
DETAILS GET MORE SKETCHY OWING TO WHAT COULD BE A SERIES OF SHORT
WAVES LIFTING OUT OF A MEAN UPPER TROF POSITION OVER THE PLAINS,
WHILE A BLOCKING PATTERN SETS UP OVER EASTERN NORTH AMERICA. THE
MODEL GUIDANCE IS IN GENERAL AGREEMENT THAT WE WOULD BE CLOSER
TO THE WET PART OF THE BLOCK WITH ACCESS TO GULF MOISTURE AND
PROXIMITY TO THE SHORT WAVES PASSING TO OUR NW. THIS RAISES THE
CONCERN FOR AT LEAST ONE PERIOD OF HEAVY RAIN IN LATE DECEMBER,
SO STAY TUNED FOR THAT. FOR NOW, OUR FORECAST WILL KEEP THE PRECIP
IN THE CHANCE RANGE UNTIL A STRONGER SIGNAL FOR THE TIMING EMERGES.
AVIATION /15Z FRIDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: THE LOW STRATUS DECK TAKING LONGER TO ERODE
THAN PREVIOUSLY EXPECTED. ANY LINGERING FOG SHOULD QUICKLY DISSIPATE
THOUGH.THEREAFTER, A COLD FRONT WILL QUICKLY MOVE ACROSS THE AREA
TODAY SHIFTING WINDS OUT OF THE W AND THEN NW ALONG WITH RAPIDLY
CLEARING CONDITIONS AND A RETURN TO VFR CONDITIONS. BRIEF SCT
SHOWERS WILL BE POSSIBLE WITH THE FROPA AT KCLT AND KHKY THIS
AFTN/EVENING. THIS WAS NOTED WITH PROB30S FOR A FEW HRS AT BOTH
SITES.
OUTLOOK: EXPECT BROAD HIGH PRESSURE AND MOSTLY DRY CONDITIONS TO
PERSIST THRU THE WEEKEND. PRECIPITATION CHANCES AND ASSOCIATED
RESTRICTIONS INCREASE EARLY NEXT WEEK.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...WINTER WEATHER ADVISORY UNTIL 1 PM EST SATURDAY FOR NCZ033-
048>052.
SC...NONE.
SYNOPSIS...PM
NEAR TERM...JPT/RWH
SHORT TERM...PM
LONG TERM...PM
AVIATION...JPT/RWH
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