Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 242019
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
319 PM EST TUE FEB 24 2015

.SYNOPSIS...
HIGH PRESSURE WILL LINGER OVER THE REGION AND WEAKEN THROUGH MID DAY
WEDNESDAY. BY WEDNESDAY EVENING...A MOIST AND WINTRY LOW PRESSURE
SYSTEM WILL DEVELOP ACROSS SOUTHERN GEORGIA AND MOVE UP THE CAROLINA
COAST THROUGH THURSDAY MORNING.  COLD CANADIAN HIGH PRESSURE BUILDS
INTO THE AREA FRIDAY THROUGH SATURDAY...WITH A WARMING TREND
BEGINNING SUNDAY THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 230 PM...A CHANNELED VORT WILL LIFT NORTH OVER THE AREA
TONIGHT...AS UPPER FLOW BACKS FROM WNW TO WSW. A POTENT COMPACT UPR
LOW WAS SEEN ON WV IMAGERY BEGINNING TO ADVANCE EASTWARD ACRS THE
FOUR-CORNERS REGION. AT THE SFC...WEAK HIGH PRES WAS ANALYZED ALONG
THE EASTERN SEABOARD...WHILE A BROAD AREA OF MODIFIED ARCTIC AIR
REMAINS ACRS THE SOUTHERN PLAINS AND NRN GULF OF MEXICO. THE WEAK
SWLY LLVL FLOW AND COLD BL FROM EARLY SNOW ACRS THE CWFA WILL HELP
KEEP A FAIR AMOUNT OF STRATUS AROUND THIS EVENING THRU TONIGHT. THIS
HAS RESULTED IN LITTLE RECOVERY IN TEMPS...WITH MOST AREAS IN THE
20S TO LWR 30S. DESPITE THIS...GROUND/ROAD TEMPS WERE STILL ABOVE
FREEZING IN MOST AREAS...ESP ACRS THE PIEDMONT...ALLOWING SNOW TO
MELT. TEMPS TONIGHT LOOK TO DROP A BIT INTO THE TEENS TO LWR 20S IN
THE MTNS AND MID TO UPR 20S ACRS THE PIEDMONT. SO SOME RE-FREEZING
OF MELTED SNOW IS EXPECTED THIS EVENING/OVERNIGHT. WE WILL ISSUE AN
SPS FOR TONIGHT FOR THE ENTIRE AREA TO HIGHLIGHT THE THREAT FOR
AREAS OF BLACK ICE.

WEDNESDAY...THE AFOREMENTIONED COMPACT LOW WILL EJECT AS A VIGOROUS
SHORTWAVE ACRS THE SOUTHERN PLAINS. THIS ENERGY WILL INTERACT WITH A
STALLED FRONTAL ZONE IN THE GULF OF MEXICO...SPINNING UP A WEAK SFC
WAVE SOUTH OF THE LA COAST BY 18Z. GUIDANCE IN GOOD AGREEMENT ON
FRONTOGENETIC FORCING BANDS SETTING UP WELL NORTH AND EAST OF THE
LOW ACRS THE I-20 CORRIDOR...LIFTING NORTH INTO THE AREA LATE AFTN.
THIS LLVL FORCING WILL BE SUPPORTED BY STRONG 850-500 MB Q-VECTOR
CONVERGENCE AND UPPER LEVEL JET DIVERGENCE. SO CONFIDENCE IS HIGH
THAT PRECIP SHUD BEGIN TO DEVELOP VERY QUICKLY ACRS THE NRN GULF
STATES TO AT LEAST THE SOUTHWESTERN HALF OF THE CWFA BY 00Z THU. I
HAVE BUMPED UP POP TO CATEGORICAL ACRS THE UPR SAVANNAH VALLEY...AND
LIKELY TO ALONG THE I-26 CORRIDOR. THE CONSENSUS OF THE GUIDANCE IS
FOR SOME RECOVERY OF TEMPS TO THE LWR 40S ACRS THE LOW ELEVATIONS
AND MID 30S ABOVE 3500 FT BY EARLY WED AFTN. FCST SNDGS SHOW THAT
THE MID LVL THICKNESSES WILL BE COOL...WHILE THE WARM SFC LAYER WILL
BE FAIRLY SHALLOW. SO EXPECT THE HIGHER ELEVATIONS TO SEE PRECIP TO
START OUT PRETTY MUCH AS SNOW...WHILE THE PIEDMONT AREAS PROBABLY
WILL START AS RAIN OR RA/SN MIX. SO ANY ACCUMS DURING THE AFTN ARE
EXPECTED TO BE MAINLY CONFINED TO THE MTNS THRU 00Z...WITH 1-2"
POSSIBLE.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 230 PM TUESDAY...THE MAIN FOCUS OF COURSE FOR THE SHORT TERM
IS THE IMPENDING WINTER EVENT WHICH BEGINS WED. AFTERNOON AND THEN
UNFOLDS ACROSS THE ENTIRE AREA WED NIGHT. THERE IS GOOD MODEL
CONSENSUS THAT THE SOUTHERN STREAM UPPER WAVE OVER THE 4 CORNERS
THIS MORNING WILL MOVE RAPIDLY EASTWARD AND INDUCE CYCLOGENESIS OVER
THE GOM EARLY WED. THE GULF LOW IS THEN FORECAST TO MOVE QUICKLY
EASTWARD ACROSS THE DEEP SOUTH WED NIGHT. THE MAIN CONCERN FOR THIS
FORECAST IS WHERE THE BEST BANDING WILL SET UP AND THE SUBSEQUENT
QPF RESPONSE. ALSO FOR THE PIEDMONT AREA...THE QUESTION OF QUICKLY
THE BOUNDARY LAYER COOLS IS A BIG PLAYER IN SNOW ACCUMS. BASED ON
SURFACE WET BULBS...IT LOOKS INITIALLY ALONG AND SOUTH OF I-85
PRECIP WILL BEGIN AS RAIN WHICH WILL USE UP SOME QPF.
HENCE...SNOWFALL ACCUMS WILL FALL OFF TO THE SOUTH WITH THE
RAIN/SNOW LINE MOST LIKELY SETTING UP SOMEWHERE ACROSS THE SOUTHERN
FRINGS OF NE GA AND THE SOUTHERN UPSTATE...FROM ELBERT COUNTY GA
EAST THROUGH ABBEVILLE AND GREENWOOD COUNTIES. THE SREF PLUMES CATCH
THIS SCENARIO WITH THE HIGHEST TOTALS OUTSIDE THE MOUTAINS ALONG AND
NORTH OF I-85 WHERE 4-6 INCHES OF SNOW IS THE MEAN FORECAST. THE
PLUMES INDICATE THAT ACTUALLY THE SW MOUNTAINS MAY ACHIEVE THE MOST
SNOW OF 6-8 INCHES WHICH IS PLAUSIBLE BASED ON UPSLOPE. THE WPC WWD
PAINTS A SWATH OF 4-6 INCH SNOW FROM THE GA MOUNTAINS EASTWARD
THROUGH CLT. HAVE FOLLOWED THIS GENERAL IDEA WITH SNOW GRIDS...
EXCEPT WENT HIGHER IN THE SW MOUNTAINS (6-8 INCHES SOME AREAS). 12Z
MODEL QPF HAS A LITTLE BETTER AGREEMENT WITH THE GFS NOW WETTER BUT
STILL NOT QUITE AS WET AS THE NAM. THE UPSHOT IS THAT CONFIDENCE IS
HIGHEST TO GO AHEAD AND PULL THE TRIGGER ON A WINTER STORM WARNING
FOR MOST OF THE AREA BEGINNING WED LATE AFTERNOON. THE EXCEPTION IS
THE SOUTHERN TIER OF COUNTIES OF ELBERT...ABBEVILLE...GREENWOOD
WHERE WILL A WINTER STORM WATCH WILL BE MAINTAINED AS RAIN/SNOW LINE
WILL BE IN VICINITY.

THE SNOW WILL END QUICKLY EARLY THU AS THE LOW PULLS AWAY TO THE
EAST. HOWEVER...CONTINUING E-NE FLOW WILL CREATE SOME WEAK SLOPE
OVER THE MOUNTAINS WHERE AREAS OF LIGHT SNOW ARE LIKELY TO PERSIST
INTO EARLY FRIDAY. WINDS SHOULD BACK TO MORE OF A NORTHERLY
DIRECTION ON FRIDAY ENDING THE MOUNTAIN PRECIP.

USED THE COLDER NAM TO GENERATE TEMPS/SFC WETBULBS FOR WED NIGHT AND
STAYED CLOSE TO THE WPC QPF. HOWEVER...BUMPED QPF UPWARDS IN THE SW
MOUNTAINS WHERE UPSLOPE WED NIGHT SHOULD PRODCUE HIGHER AMOUNTS.
OTHERWISE...USED A MODEL CONSENSUS FOR FORECAST FIELDS.


&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 2 PM TUESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
SATURDAY WITH A PERSISTENT AND VERY BROAD UPPER TROF PATTERN OVER
MOST OF THE CONUS. AS WE MOVE INTO SUN...THE PATTERN FLATTENS OVER
THE SOUTHEAST REGION AS WEAK UPPER RIDGING TRIES TO BUILD OVER THE
GULF OF MEX. THE LONG RANGE MODELS ARE MOSTLY ON THE SAME PAGE AND
HAVE THE RIDGE GRADUALLY STRENGTHENING THRU THE REMAINDER OF THE
PERIOD AS A SOUTHERN STREAM H5 TROF DIGS DOWN OVER THE EXTREME
DESERT SW.

AT THE SFC...AN IMPRESSIVE 1040MB CANADIAN HIGH WILL BE IN PLACE
OVER THE REGION BY EARLY SAT WITH NORTH TO NELY LOW LVL FLOW SETTING
IN OVER THE CWFA. BY EARLY SUN...THE HIGH SLIDES FARTHER EAST WITH
SOME SORT OF CAD PATTERN SETTING UP OVER THE CAROLINAS. BY EARLY
MON...BOTH THE GFS AND ECMWF HAVE THE CAD DISSIPATING AS THE PARENT
HIGH MOVES FARTHER OFFSHORE. BEYOND THIS POINT...THE SFC PATTERN
BECOMES MORE AMBIGUOUS WITH SOME SORT OF BROAD DEFORMATION ZONE
SETTING UP JUST TO OUR NW WITH DEEP LYR MOISTURE OVERSPREADING THE
REGION BY EARLY MON. SIMULTANEOUSLY...ANOTHER HIGH TRACKS EASTWARD
ACROSS THE GREAT LAKES AND IS OVER NEW ENGLAND BY EARLY TUES. THE
MODELS ALSO GENERATE ANOTHER SOUTHERN PLAINS LOW EARLY TUES AND MOVE
ITS ASSOCIATED COLD FRONT TO OUR DOORSTEP BY THE VERY END OF THE
PERIOD. AS FOR THE SENSIBLE WX...SAT SHOULD BE DRY WITH TEMPS
REMAINING BELOW CLIMATOLOGY FOR LATE FEB. THE FCST FOR THE REMAINDER
OF THE PERIOD IS TRICKY. PRECIP CHANCES WILL RAMP UP TO SOLID CHANCE
BY SUN AFTERNOON WITH THE POSSIBILITY OF FROZEN PRECIP EARLIER IN
THE DAY. HIGHS WILL LIKELY REACH THE MID TO UPPER 40S...SO ALL
PRECIP SHOULD TRANSITION TO RAIN LATER IN THE DAY. THE REST OF THE
PERIOD WILL BE CHARACTERIZED BY MOIST PROFILES...MOSTLY OVERCAST
SKIES...AND SOLID CHANCES FOR WIDESPREAD PRECIP THRU THE REST OF THE
PERIOD. TEMPS SHOULD ALSO REBOUND TO ABOVE NORMAL BY EARLY NEXT WEEK
WITH HIGHS IN THE 60S ON BOTH MON AND TUES.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
AT KCLT...THE SN HAS ENDED ACRS THE KCLT AREA...BUT THE LITTLE SNOW
THAT FELL EARLIER WILL CONTRIBUTE TO KEEPING LOW STRATUS AROUND
TONIGHT INTO WEDNESDAY MORNING. GUIDANCE IN GOOD AGREEMENT ON MVFR
CIGS THIS AFTN/EVE...THEN LOWERING TO IFR AND PROBABLY EVEN TO LIFR
BY DAYBREAK WEDNESDAY. THE WINDS WILL BE LIGHT...BUT PROBABLY UP
JUST ENUF TO PRECLUDE DENSE FOG DEVELOPMENT. STILL MAY SEE SOME VSBY
RESTRICTIONS...SO WILL ADD 4SM BR FOR PART OF THE MORNING. CIGS SHUD
IMPROVE BRIEFLY WITH SOME MIXING BY MIDDAY. WINDS ARE EXPECTED TO
SHIFT TO SE AROUND TIME OF 18Z TAF VALID TIME...THEN CONTINUE TO
VEER TO SW BY LATE EVENING...THEN BACK TO N/NE BRIEFLY BEFORE GOING
BACK TO SE TOWARD END OF 18Z TAF PERIOD. PRECIP ASSOCIATED WITH NEXT
STORM SYSTEM IS NOT EXPECTED TO REACH KCLT BEFORE 18Z WED.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH MVFR/IFR CIGS LINGERING
THIS AFTN/EVE AND THRU THE OVERNIGHT. THE SN HAS ENDED FOR THE MOST
PART...EXCEPT FOR LINGERING FLURRIES ALONG THE BLUE RIDGE. THE
MELTING SNOW WILL HELP SUPPLY MOISTURE TO THE BL...AND WINDS WILL BE
LIGHT. HOWEVER...GUIDANCE GENERALLY INDICATES LOW STRATUS VERSUS
DENSE FOG. WINDS THROUGH THE PERIOD WILL REMAIN LIGHT/MODERATE AND
VEER FROM NE TO SSW...THEN BACK TO N/NE AGAIN WEDNESDAY MORNING
AFTER DAYBREAK. AT KAVL...A CROSS-VALLEY FLOW IS HELPING IT GO VFR
FOR THE AFTN...BUT THE FLOW WILL VEER TO NW AND UP-VALLEY CIGS ARE
EXPECTED TO BE MVFR THIS EVENING. WINDS WILL START OUT SE AT
KAVL...THEN SHIFT TO NW THIS EVENING.

OUTLOOK...ANOTHER ROUND OF WINTRY WEATHER IS LOOKING EVER MORE
LIKELY ON WEDNESDAY EVENING LEADING TO POSSIBLE FLIGHT RESTRICTIONS
AT ALL SITES WITH SOME ACCUMULATING SNOWFALL. BEYOND THAT...LOW
LEVEL MOISTURE WILL LINGER THROUGH THE REMAINDER OF THE WEEK...WITH
VARIABLE AMOUNTS OF CIG HGT RESTRICTIONS THRU FRIDAY.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WINTER STORM WARNING FROM 4 PM WEDNESDAY TO 7 AM EST THURSDAY
     FOR GAZ010-017-018-026-028.
     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH LATE
     WEDNESDAY NIGHT FOR GAZ029.
NC...WINTER STORM WARNING FROM 4 PM WEDNESDAY TO 7 AM EST THURSDAY
     FOR NCZ033-035>037-048>053-056>059-062>065-068>072-082-
     501>510.
SC...WINTER STORM WARNING FROM 4 PM WEDNESDAY TO 7 AM EST THURSDAY
     FOR SCZ001>010-012>014.
     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH LATE
     WEDNESDAY NIGHT FOR SCZ011-019.

&&

$$
SYNOPSIS...JPT
NEAR TERM...ARK
SHORT TERM...LG
LONG TERM...JPT
AVIATION...ARK


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