631
FXUS62 KGSP 191804
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
104 PM EST THU DEC 19 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 TONIGHT/
AS OF 1250 PM: NO BIG CHANGES WITH THE MIDDAY UPDATE. CLOUD
COVER CONTINUING TO GRADUALLY INCREASE, ALTHOUGH SOME AREAS ARE
SEEING CLOUDS MIX OUT. FOR THE REST OF THE AFTN, MOIST EASTERLY TO
SOUTHEASTERLY UPGLIDE FLOW SHOULD CONTINUE TO PRODUCE INCREASING
ACROSS THE FORECAST AREA. TEMPS LOOK ON TRACK.
OTHERWISE, SFC FLOW WILL TURN PREDOMINANTLY NE OVER THE PIEDMONT,
AND MORE SE NEAR THE BLUE RIDGE ESCARPMENT, AS HIGH PRES MIGRATES
TO THE EAST COAST TODAY IN WEDGE-LIKE FASHION. SOMEWHAT LIKE WE
HAVE SEEN FOR THE PAST FEW DAYS, THE SFC FRONT WILL BE STALLED TO
OUR SOUTH TODAY AND WEAK MOIST UPGLIDE WILL OCCUR OVER IT. ENOUGH
OF A MOIST LAYER IS EXPECTED TO REMAIN UNDER THE SUBSIDENCE
INVERSION THAT SOME CLOUD COVER WILL REDEVELOP IN THE PIEDMONT
THIS AFTERNOON. WITH THAT, AND NORTHEAST SFC FLOW, TEMPERATURES ARE
NOT EXPECTED TO MAKE IT OUT OF THE 50S IN MOST AREAS TODAY, WHICH
MAY SEEM A BIT OF A SHOCK AFTER THE PAST COUPLE OF AFTERNOONS--BUT
ACTUALLY TEMPS TODAY STILL WILL BE A LITTLE ABOVE NORMAL.
FLOW WITHIN THE PBL, UNDER THE INVERSION, IS PROGGED TO VEER TO
SOUTHERLY THIS EVENING INTO THE EARLY OVERNIGHT. THIS SHOULD LEAD
TO A SOLIDIFYING STRATUS DECK ACROSS THE PIEDMONT, ALTHOUGH THAT
AREA PROBABLY WILL REMAIN MIXED ENOUGH THAT FOG PROBABLY WON'T BE
OF MUCH PUBLIC IMPACT IF IT FORMS AT ALL. MOIST LAYER APPEARS TOO
SHALLOW FOR A MENTIONABLE POP, BUT SOME DRIZZLE MIGHT RESULT. MINS
REMAIN A FEW DEGREES ABOVE NORMAL. THE LOW CLOUDS MAY BEGIN TO
BE SCOURED FROM THE WEST AROUND DAYBREAK FRI AS DRIER AIR WRAPS
AROUND APPROACHING CLIPPER SHORTWAVE, WITH THE MAIN IMPACTS OF
THAT WAVE BEING IN THE SHORT-TERM PERIOD.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
AS OF 200 AM EST THURSDAY: A STRONG SHORTWAVE WILL BE IN THE MIDST
OF PUSHING THROUGH THE MIDWEST AND UPPER GREAT LAKES FRIDAY MORNING,
WITH AN ALBERTA CLIPPER SURFACE LOW RIDING UNDERNEATH. EXPECT
BOTH FEATURES TO SLIP EAST INTO THE NORTHEAST AND MID-ATLANTIC,
JUST NORTH OF THE AREA LATER IN THE DAY. A VORT MAX WILL ROUND
THE BASE OF THE SHORTWAVE AND PIVOT ACROSS THE CFWA BY FRIDAY
AFTERNOON. STOUT CAA AND NORTHWEST FLOW PRECIP WILL TAKE PLACE
FRIDAY AFTERNOON ALONG THE NC/TN BORDER. PRECIPITATION AT THE
ONSET FRIDAY AFTERNOON MAY BEGIN WITH MIXED P-TYPES OUTSIDE OF
THE HIGHEST PEAKS, BUT A QUICK CHANGEOVER TO SNOW BY THE EVENING
COMMUTE IS EXPECTED AS SNOW LEVELS DROP DRASTICALLY. THE UPPER
DYNAMICS WILL ALLOW FOR GOOD FORCING FOR ASCENT TO GO ALONG WITH
OROGRAPHICALLY ENHANCEMENT, ESPECIALLY IN THE FAVORED NORTHWEST
FACING SLOPES. IN THIS TYPE OF SETUP EXPECT SNOW SHOWERS TO BREAK
CONTAINMENT AND ENTER THE MAJOR MOUNTAIN VALLEYS AND A GOOD PORTION
OF THE NC MOUNTAINS LATE FRIDAY AFTERNOON AND EVENING. CAMS CONTINUE
TO PRODUCE A FEW SHOWERS EAST OF THE MOUNTAINS AS WELL, BUT WITH
THE COLD AIR CHASING THE PRECIP AND ANTECEDENT WARM TEMPERATURES,
THE TRANSITION TO SNOW WILL BE DIFFICULT AS THE PRECIP PUSHES EAST
OF THE CFWA BEFORE THE COLD AIR CAN HELP MAKE THIS TRANSITION. ONE
THING TO NOTE, VERY COLD AIR ALOFT, FORCING FOR ASCENT, AND WEAK
INSTABILITY COULD ALLOW FOR ISOLATED GRAUPEL OR FLAKES TO MIX IN
AND REACH THE SURFACE. MOST OF THE MODEL GUIDANCE HAS THIS ACTIVITY
DEVELOPING OVER THE CLT METRO AND I-77 CORRIDOR AROUND THE EVENING
COMMUTE FRIDAY. OTHERWISE, THE REST OF THE CFWA SHOULD REMAIN DRY,
BUT AN UPTICK IN WINDS WILL BE EVIDENT AS THE PRESSURE GRADIENT
OVER THE REGION TIGHTENS AS CAA FILTERS IN. TEMPERATURES MANAGE
TO TOP OUT AROUND NORMAL EAST OF THE MOUNTAINS, WHILE SLIGHTLY
BELOW VALUES RESIDE IN THE MOUNTAINS.
NORTHWEST FLOW SNOW SHOULD PERSIST OVERNIGHT FRIDAY, MAINLY
ALONG THE NC/TN BORDER AS THE VORT MAX PUSHES EAST OF THE CFWA
AND THE DYNAMICS IN PLACE WEAKENS. AS A RESULT, ANY ONGOING SNOW
WILL BE DUE TO MECHANICAL LIFT OUT OF THE NORTHWEST AND SHOULD
SLOWLY DWINDLE IN COVERAGE THROUGH SATURDAY MORNING BEFORE THE
PRESSURE GRADIENT RELAXES AND DRY AIR ENTRAINMENT SHUTOFF THE SNOW
MAKER. MUCH COLDER THICKNESSES WILL SETTLE INTO THE AREA IN RESPONSE
TO THE ASSOCIATED RAPID HEIGHT FALLS FROM THE SHORTWAVE. STRONG
CP SURFACE HIGH WILL BEGIN TO PUSH ACROSS THE GREAT LAKES BEHIND
THE SHORTWAVE SATURDAY NIGHT AND HELP AID THE COLDER AIR PUSHING
INTO THE REGION. OVERNIGHT LOWS FRIDAY WILL ONLY BE A FEW TICKS
BELOW NORMAL AS WINDS REMAIN ELEVATED AND THE BOUNDARY LAYER WILL
STRUGGLE TO FULLY DECOUPLE. AFTERNOON HIGHS ON SATURDAY WILL RUN
5-10 DEGREES BELOW NORMAL AS THE COLD AIRMASS MOVES ACROSS THE
AREA. SATURDAY NIGHT LOWS RUN 5-10 DEGREES BELOW-NORMAL AS THE
AIRMASS BECOMES FIRMLY ENTRENCHED ACROSS THE AREA.
LONG TERM /SUNDAY THROUGH THURSDAY/
AS OF 310 AM EST THURSDAY: A SHORTWAVE ROUNDS THE PERIPHERAL OF
BROAD UPPER TROUGHINESS LEFTOVER FROM THE SHORT-TERM SHORTWAVE OVER
THE EASTERN CONUS, WHICH WILL HELP REINFORCE THE COLDER AIR ALOFT
ON SUNDAY. ALL WHILE A LARGE AND STRONG SURFACE HIGH (~1040MB)
SLIPS INTO THE GREAT LAKES AND EVENTUALLY THE NORTHEASTERN CONUS
SUNDAY INTO SUNDAY NIGHT. THE LOCATION OF THE HIGH WILL FILTER IN
A CAD-LIKE CONFIGURATION INTO THE CFWA AND REMAIN IN PLACE GOING
INTO THE EARLY PART OF NEXT WEEK. A SHORTWAVE RIDGE BUILDS IN FROM
THE WEST MONDAY AND TUESDAY, ALLOWING FOR THE AIRMASS TO GRADUALLY
MODIFY, ESPECIALLY BY TUESDAY AS THE SURFACE HIGH WEAKENS SLIGHTLY
AND MOVES FURTHER OFFSHORE THE NEW ENGLAND COAST. MODEL GUIDANCE
DIFFER ON THE SYNOPTIC EVOLUTION BEYOND THE EARLY PART OF NEXT WEEK,
BUT THE OVERALL SETUP WILL BECOME MORE AMPLIFIED WITH A SERIES OF
SHORTWAVES SWINGING FROM WEST TO EAST AND REACHING THE EAST COAST
BY THE LATTER HALF OF THE PATTERN AND BEYOND D7. TEMPERATURES WILL
RUN 10-15 DEGREES BELOW NORMAL SUNDAY AND MONDAY, WITH A CATEGORY
OR SO UPTICK ON TUESDAY. THE WARMING TREND SHOULD CONTINUE INTO
WEDNESDAY AS WELL AS WEAK WAA FILTERS BACK INTO THE CFWA TO GO
ALONG WITH WARMER THICKNESSES.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: A MOIST EASTERLY TO SOUTHEASTERLY FLOW
IS EXPECTED TO PRODUCE A GRADUAL INCREASE IN LOW CIGS ACROSS
THE TERMINAL FORECAST AREA THIS AFTN THRU TONIGHT. CONFIDENCE IS
BELOW AVERAGE ON THE EXACT TIMING OF MVFR TO POSSIBLY IFR CIGS,
BUT CONFIDENCE IS HIGH THAT RESTRICTIVE CIGS WILL IMPACT ALL SITES
AT SOME POINT TONIGHT THRU FRIDAY MORNING. WINDS ARE EXPECTED TO
GO LIGHT THIS EVENING, BUT THE AIR MASS UNDER THE CLOUD DECK MAY
BE TOO DRY FOR FOG. CANNOT RULE OUT SOME PATCHY FOG, ESPECIALLY
NEAR THE ESCARPMENT. THE STRATUS SHOULD START TO LIFT/SCATTER
OUT AROUND MIDDAY FRIDAY, AS A COLD FRONT PUSHES INTO THE AREA
FROM THE NORTHWEST. THE FRONT WILL TOGGLE WINDS OUT OF THE WSW
TO WNW BY EARLY AFTN. AT CLT...GUIDANCE IS IN GOOD AGREEMENT ON
SCATTERED SHOWERS FORMING IN THE NW PIEDMONT. SO WILL ADD A PROB30
FOR SOME SHRA.
OUTLOOK: HIGH PRESSURE AND DRY CONDITIONS LAST THROUGH THE WEEKEND,
WITH THE EXCEPTION BEING A CHANCE FOR SNOW ALONG THE TN BORDER
FRI PM THRU SAT AM WITH A REINFORCING COLD FRONT. PERIODIC CIG
RESTRICTIONS CAN'T BE RULED OUT UNTIL THAT FRONT PASSES.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...DEO
NEAR TERM...ARK/WIMBERLEY
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...ARK
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