945
FXUS62 KGSP 190810
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
310 AM 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 245 AM: WATER VAPOR IMAGERY SHOWS WELL DEFINED TROUGH AXIS
JUST EAST OF THE APPALACHIAN SPINE, WITH SURFACE COLD FRONT JUST
AHEAD OF THAT AXIS PER MSLP TRENDS AND WIND SHIFT, HAVING PUSHED
THRU THE I-85 CORRIDOR OF OUR CWA. BEFORE IT REACHED THE WESTERN
MISSISSIPPI VALLEY, THE TROUGH HAD BEEN TWO SHORTWAVES WHICH PHASED,
AND IT NOW APPEARS THEY ARE DE-PHASING, WITH THE SOUTHERN ONE MAKING
SLOWER PROGRESS ACROSS THE SOUTHEAST THAN THE NORTHERN ONE. THIS IS
LEADING THE FRONT TO PIVOT SUCH THAT IT MAY NOT MAKE MUCH FURTHER
PROGRESS ACROSS OUR SOUTHERN SC ZONES THRU DAYBREAK; HENCE WE ARE
BECOMING A LITTLE MORE CONCERNED THAT THE PATCHY DENSE FOG FROM
ANDERSON TO ROCK HILL WILL PERSIST INTO THE MORNING COMMUTE. AN SPS
WAS USED TO ADDRESS THAT GENERALLY SOUTH OF CHARLOTTE EARLIER THIS
MORNING, AND THAT REMAINS VALID TIL 4 AM. WILL CONSIDER ISSUING
ANOTHER FROM THE LAKELANDS EAST TO REPLACE THAT ONE WHEN IT EXPIRES.
EAST OF THE MOUNTAINS, REMAINING CLOUDS WILL SCATTER AS THE
TROUGH AXIS MOVES ALONG; SHALLOW STRATUS DECK WILL REMAIN BANKED
AGAINST THE MOUNTAIN SPINE MOST OF THE MORNING. SFC FLOW WILL
TURN PREDOMINANTLY NE OVER THE PIEDMONT, AND MORE SE NEAR THE
BLUE RIDGE ESCARPMENT, AS HIGH 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.
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 WEDNESDAY/
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 /08Z THURSDAY THROUGH MONDAY/
AT KCLT AND ELSEWHERE: COLD FRONT APPEARS TO HAVE PUSHED PAST ALL
SITES EXCEPT KCLT AND POSSIBLY KAND, AS OF 0545Z. A FOG/STRATUS
LAYER DOES EXIST IN REMAINING SOUTHERLY FLOW REGIME AHEAD OF
THE FRONT, AND PER SATELLITE IS IMMEDIATELY SOUTH OF KCLT AND
HAD APPEARED TO BE ADVECTING NORTH. A TEMPO WAS INCLUDED THERE
MAINLY FOR THE CHANCE THIS LAYER REACHES THE FIELD BEFORE THE
FRONT INDUCES DRYING/MIXING; ADDITIONAL CHANCE OF -SHRA IS LIKELY
OF LITTLE CONSEQUENCE. WINDS WILL FLIP TO NW TO N FOLLOWING THE
FROPA AT ALL SITES, VEERING AROUND TO NE AFTER DAYBREAK; A FEW
GUSTS ARE LIKELY. AIRMASS BEHIND THE FRONT WILL BE SHALLOW; FRONT
STALLS JUST SOUTH OF THE TERMINAL AREA LATER TODAY. MOIST INVERSION
ONCE AGAIN MAY RESULT IN A PATCHY LOW VFR OR EVEN MVFR CLOUD DECK
SIMILAR TO THE PREVIOUS COUPLE OF AFTERNOONS. WARM UPGLIDE AT THE
TOP OF THE PBL WILL STRENGTHEN TONIGHT AS NEXT TROUGH APPROACHES
FROM THE WEST, AND THIS DEVELOPMENT LIKELY WILL REINSTATE MVFR
CIGS OVER MUCH OF THE AREA TONIGHT.
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...CAC
NEAR TERM...WIMBERLEY
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...WIMBERLEY
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