Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 250601
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
101 AM EST WED FEB 25 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 TODAY/...
AS OF 100 AM EST WEDNESDAY...NO SIGNIFICANT CHANGES MADE TO THE FCST
WITH THIS UPDATE.  TEMPERATURES ACROSS THE REGION CONTINUE TO HOVER
AT OR JUST BELOW FREEZING WITH LIGHT DRIZZLE/MIST BEING OBSERVED
ALONG AND SOUTH OF THE INTERSTATE 85 CORRIDOR WHERE BL MOISTURE IS
MAXIMIZED.  THIS COMBINED WITH EARLIER WET ROADWAYS WARRANTS
CONTINUATION OF BLACK ICE MENTION IN CURRENT WSW PRODUCT.  DID TWEAK
TEMPERATURES AND DEWPOINTS TO REFLECT LATEST OBSERVATIONS.
OTHERWISE...WILL BE READDRESSING SNOW ACCUMULATIONS REGARDING THE
UPCOMING STORM WITH THE FULL FCST PACKAGE AROUND 330AM.

PREVIOUS DISCUSSION...

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 /TONIGHT 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.



AND CHESTER.

&&

.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 /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...SIGNIFICANT WINTER WEATHER RESTRICTIONS EXPECTED WITHIN
THIS TAF CYCLE AS POTENT SURFACE WAVE AND ASSOCIATED UPPER SUPPORT
SLIDE THROUGH THE REGION.  TAF INITIALIZES AMIDST MVFR CIGS AND
LIGHT SW FLOW AT THE SFC.  EXPECTING CIG RESTRICTIONS TO LIFT BY
AROUND DAYBREAK ALTHOUGH WITH DECREASED VISB AS LIGHT FOG DEVELOPS
AROUND THE REGION.  WOULD ALSO NOT BE SURPRISED TO SEE SOME FZFG IF
IT BECOMES DENSE ENOUGH AS SURFACE TEMPS WILL BE
SUBFREEZING...ALTHOUGH WAS LEFT OUT OF TAF AT THIS TIME.  AFTER
DAYBREAK CONDITIONS WILL IMPROVE YIELDING THE CALM BEFORE THE STORM
WITH MID/HIGH LEVEL CLOUDS PREVAILING THROUGH MID AFTERNOON.
EXPECTING PRECIP TO ENTER THE REGION LATE DAY IN THE FORM OF A RASN
MIX BEFORE QUICKLY CHANGING OVER TO RAIN.  AT THAT TIME...CIGS/VISB
WILL DROP TO MVFR/IFR...THEN TO LIFR AS HEAVY SNOW SHOWERS MOVE
INTO THE REGION.  OPTED TO INCLUDE RASN MENTION AT 00Z WITH MVFR
CIGS AND IFR VISB BEFORE LOWERING TO LIFR CIGS WITH PREDOMINATE SN
AT 02Z...LASTING THROUGH THE PERIOD.  LATEST ACCUMULATION FCST
INDICATES THAT THE I85 CORRIDOR WILL BE THE MAXIMA THUS WOULD NOT BE
SURPRISED TO SEE MODERATE/HEAVY SNOWFALL AT TIMES WITH RATES
EXCEEDING 1-2 INCHES PER HOUR CAUSING SIGNIFICANT VISB
RESTRICITONS.

AT KAVL AND KHKY...ALSO EXPECTING SIGNIFICANT FLIGHT RESTRICITONS
DUE TO SNOWFALL MOVING INTO THE REGION MID/LATE DAY WEDNESDAY.
INITIALIZED KAVL VFR WHILE GOING WITH IFR CIGS AT KHKY FOR THE NEXT
FEW HOURS BEFORE IMPROVEMENT IS INTRODUCED...ALTHOUGH CONTINUING
WITH MVFR VISB DUE TO LIGHT FOG/MIST.  OTHERWISE...BEYOND DAYBREAK
VFR WILL PREVAIL AHEAD OF PRECIP ARRIVAL BY LATE AFTERNOON IN THE
FORM OF SN.  THE MOST SIGNIFICANT ACCUMULATIONS ARE FCST FURTHER
SOUTH ALONG THE I85 CORRIDOR...HOWEVER WOULD NOT BE SURPRISED TO SEE
MODERATE ACCUMS WITH RATES NEARING 1-2 INCHES PER HOUR CAUSING
SIGNIFICANT VISB RESTRICITONS.

SC SITES...ALL SC SITES WILL BE IMPACTED BY SIGNIFICANT SNOWFALL
THROUGH THIS PERIOD LEADING TO ABUNDANT FLIGHT RESTRICITONS.
INITIALIZED ALL TAFS AT MVFR/IFR DUE TO LINGERING LOW LEVEL MOISTURE
IN THE BL.  THESE CIG CONDITIONS ARE EXPECTED TO IMPROVE THROUGH
MORNING ALTHOUGH GIVING WAY TO DECREASED VISB AT KAND WITH PATCHY
DENSE FOG POSSIBLE AT KGMU/KGSP.  TEMPERATURES WILL REMAIN BELOW
FREEZING THROUGH MORNING THUS FZFG IS A POSSIBILITY...THEREFORE
OPTED TO INCLUDE VIA TEMPO.  VFR WILL PREVAIL THROUGH LATE MORNING
BEFORE PRECIP SLIDES IN FROM THE WEST IN THE FORM OF RASN MIX BEFORE
QUICKLY TRANSITIONING TO ALL SNOW.  AS MENTIONED ABOVE...THE I85
CORRIDOR LOOKS TO BE THE MAXIMA OF EXPECTED SNOWFALL THEREFORE WOULD
NOT BE SURPRISED TO SEE MODERATE/HEAVY SNOWFALL RATES OF AROUND 1-2
INCHES PER HOUR CAUSING SIGNIFICANT VISB RESTRICITONS.

OUTLOOK...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 WEATHER ADVISORY UNTIL NOON EST TODAY FOR GAZ010-017-
     018-026-028-029.
     WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 7 AM EST
     THURSDAY FOR GAZ010-017-018-026-028.
     WINTER STORM WATCH FROM THIS EVENING THROUGH LATE TONIGHT FOR
     GAZ029.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ033-
     035>037-048>053-056>059-062>065-068>072-082-501>510.
     WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 7 AM EST
     THURSDAY FOR NCZ033-035>037-048>053-056>059-062>065-
     068>072-082-501>510.
SC...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR SCZ001>014-
     019.
     WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 7 AM EST
     THURSDAY FOR SCZ001>010-012>014.
     WINTER STORM WATCH FROM THIS EVENING THROUGH LATE TONIGHT FOR
     SCZ011-019.

&&

$$
SYNOPSIS...JPT
NEAR TERM...ARK/CDG/JAT
SHORT TERM...LG
LONG TERM...JPT
AVIATION...CDG


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