Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 212014 CCA
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
303 PM EST SUN DEC 21 2014

.SYNOPSIS...
A MOIST AIR MASS WILL REMAIN ACROSS THE REGION BEFORE A COLD FRONT
CROSSES EAST ON WEDNESDAY. DRY CANADIAN HIGH PRESSURE WILL BUILD IN
THURSDAY AND PERSIST INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 230 PM...THE STRATUS DECK CONTINUES TO ERODE SLOWLY ACRS THE
MTNS AND LOWER PIEDMONT THIS AFTN...RESULTING IN SLIGHTLY WARMER
TEMPS UNDER MORE SUNSHINE. MOST THE AREA IS STILL OVERCAST OR MOSTLY
CLOUDY...WITH TEMPS IN THE 40S TO LWR 50S.

GUIDANCE IN GOOD AGREEMENT ON A DIGGING TROF TO THE WEST AND A
BUILDING RIDGE ALONG THE EAST COAST TONIGHT THRU MONDAY. SHORTWAVE
ENERGY WILL RIDE FROM SW TO NE THRU THE FLOW ATOP THE SOUTHEAST
STATES...INDUCING A WEAK WAVE ALONG A COASTAL FRONT OFF THE SC COAST
ON MONDAY. INCREASING SOUTHERLY UPGLIDE AND 850 MB WAA FLOW ATOP THE
CWFA. POPS QUICKLY RAMP UP TO CATEGORICAL ACRS THE SOUTHERN HALF OF
THE CWFA...AND LIKELY TO THE NORTH BY LATE EVENING. THE COVERAGE
WILL BE AIDED BY SOME DEEP LAYER Q-VECTOR CONVERGENCE WITHIN THE
SWLY MID-UPR FLOW. HOWEVER...THE MOISTURE DEPTH WILL BE FAIRLY
SHALLOW...AND FORCING OVERALL WEAK. SO QPF AMOUNTS SHUD BE GENERALLY
A FEW HUNDREDTHS TO A TENTH OF AN INCH. ALTHO...A TENTH TO QUARTER
INCH POSSIBLE AROUND THE CHARLOTTE METRO AREA. ONE THING TO MENTION
IS THAT THERMAL PROFILES ARE MARGINAL FOR SOME FREEZING RAIN AND
SLEET ACRS THE NRN MTNS...MAINLY AVERY COUNTY. THE 12Z NAM AND
LATEST RAP KEEP THINGS JUST ABOVE FREEZING. I WOULDN/T BE SURPRISED
IF A FEW SPOTS NEAR THE EASTERLY UPSLOPE AREAS IN AVERY/CALDWELL MAY
HAVE BRIEF FZRA/DZ TOWARD DAYBREAK MONDAY. HOWEVER...CONFIDENCE IS
JUST NOT HIGH ENUF TO ISSUE A FREEZING RAIN ADVISORY AT THIS TIME.
IF THE 18Z NAM COMES IN COLDER...OR IF TRENDS SEEM TO WARRANT
IT...THE EVENING SHIFT MAY WANT TO ISSUE ONE OR AN SPS.
OTHERWISE...IT SHUD BE JUST A COLD RAIN WITH TEMPS IN THE 30S TO LWR
40S.

ON MONDAY...THE MID LVLS DRY OUT...AND THE BETTER FORCING EXITS TO
THE EAST. HOWEVER...A WEDGE IS EXPECTED TO REMAIN...WITH LLVL
UPGLIDE CONTINUING WITHIN SWLY FLOW. THIS LOOKS LIKE A GOOD SETUP
FOR AREAS OF -DZ PERSISTING...ALSO KEEPING TEMPS DOWN. GOING CLOSE
TO THE RAW MODEL TEMPS FOR HIGHS...AND KEEPING A CHC OF -RA AND DZ
THRU THE DAY. HIGHS WILL LIKELY STRUGGLE TO GET INTO THE 40S ACRS
THE I-40 CORRIDOR...AND ONLY THE MID TO UPR 40S ELSEWHERE.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM EST SUNDAY...MON NIGHT THROUGH TUESDAY NIGHT...LATEST
12Z MODELS CONTINUE TO INDICATE THAT SURFACE COLD AIR DAMMING WEDGE
WILL CONTINUE ACROSS THE AREA AS 1030MB HIGH WILL REMAIN ANCHORED
OVER THE NE. MEANWHILE...STRONG SSWLY FLOW ALOFT DEVELOPS ACROSS THE
SE BY TUE AS A DEEP UPPER TROUGH MOVES EAST ACROSS THE CENTRAL CONUS
WHILE AN UPPER RIDGE AMPLIFIES OVER THE WESTERN ATLANTIC. THIS WILL
LEAD TO INCREASING 290K ISENTROPIC LIFT/ATLANTIC MOISTURE ADVECTION
OVER OUR CWA THRU TUESDAY. HENCE...HAVE CARRIED CHANCE POPS FOR
LIGHT RAIN WITH DRIZZLE MON NIGHT INTO TUE MORNING...RAMPING UP INTO
THE CATEGORICAL POPS WITH STEADY RAIN TOWARDS TUE NIGHT. WITH
ONGOING PRECIP WITHIN THE CAD...AFTERNOON TEMPS ON TUE WILL RUN 7-10
DEGREES BELOW NORMAL OVER THE PIEDMONT WITH 3-5 DEGREES BELOW OVER
THE WESTERN NC MTNS.

WEDNESDAY...THE UPPER TROUGH OVER THE MISSISSIPPI VALLEY WILL
ADVANCE EASTWARD...BECOMING POSITIVELY TILED AS IT PUSHES THROUGH
THE EASTERN CONUS. THIS WILL LIFT A SURFACE LOW INTO THE OHIO VALLEY
BY 18Z...PUSHING ITS ASSOCIATED COLD FRONT THROUGH THE FORECAST AREA
BETWEEN 18Z WED AND 00Z THU. ALTHOUGH THERE WILL BE STRONG LLVL WIND
SHEAR ALONG AND AHEAD OF THE FRONT...THE BEST UPPER FORCING WILL NOT
REACH THE AREA UNTIL 00Z THU AND AREAS SBCAPE REGIME WILL REMAIN
SOUTH OF THE AREA. THEREFORE...HIGH SHEAR LOW CAPE SEVERE EVENT
APPEARS LOW AT THIS TIME. AS FOR QPF...MODELS STILL DEPICT
WIDESPREAD CONVECTIVE ACTIVITY ALONG THE GULF COAST/SE COAST...WHICH
COULD BLOCK DEEP MOISTURE TRANSPORT INTO OUR AREA. WITH THE
UNCERTAINTY...HAVE GONE WITH THE MODEL CONSENSUS QPF...YIELDING 1-2
INCHES ACROSS THE REGION WITH UP TO 3" OVER THE BLUE RIDGE
ESCARPMENT. CATEGORICAL POPS WERE HIGHLIGHTED THRU 18Z WED...
QUICKLY RAMPING DOWN TO THE CHANCE RANGE FROM WEST TO EAST THRU 00Z
THU AS THE FRONT PUSHES TO THE EAST. WITH INCREASING WAA
FLOW...AFTERNOON TEMPS WILL WARM INTO THE U50S/60S EAST OF THE MTNS
AND 50S OVER THE MTNS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 200 PM SUNDAY...THE LATE WEEK WILL SEE THE SHARP UPPER TROUGH
PUSH OFF THE EAST COAST...LEAVING QUASI-ZONAL FLOW OVER THE ERN THIRD
OF THE CONUS. DRY HIGH PRESSURE WILL CROSS THE SOUTHEAST BEFORE
HEIGHTS FALL OVER THE MISSISSIPPI VALLEY AS NEXT LOW ROLLS OFF THE
ROCKIES AND ACRS THE GREAT LAKES. DIFFERENCES BETWEEN THE GFS AND EC
ARE MINOR IN TERMS OF SENSIBLE WX CHRISTMAS DAY AND FRIDAY...BOTH
INDICATING NW FLOW PRECIP TAPERING OFF CHRISTMAS MRNG FOLLOWED BY DRY
WX MOST OF FRIDAY. IN COLD ADVECTIVE PATTERN HIGHER ELEVATIONS WILL
LIKELY SEE BREEZY/GUSTY CONDITIONS ON CHRISTMAS. THE COLD FRONT
ASSOCIATED WITH THE GRT LAKES LOW WILL ARRIVE BY FRIDAY NIGHT ALBEIT
WITHOUT MUCH OOMPH...THE GFS PRETTY MUCH WASHING THE FRONT OUT OVER
THE CAROLINAS. THE EC HOWEVER DIVERGES AT THIS POINT...STALLING THE
FRONT ALONG THE COAST AND EVENTUALLY DEVELOPING A COASTAL LOW NEAR
THE OUTER BANKS SUNDAY IN RESPONSE TO A SRN STREAM SHORTWAVE TRAILING
THE FRONT. BOTH THE 21/00Z AND 21/12Z RUNS FEATURE THIS EVOLUTION. SO
WHILE THE GFS WOULD SUGGEST NEXT WEEKEND WILL BE QUIET AND DRY...EC
INDICATES SOME PTYPE ISSUES MAY EXIST SUNDAY WITH WINTRY PARTIAL
THICKNESSES AND THERMAL PROFILES. TEMPS WILL BE AT OR A LITTLE ABOVE
CLIMO FROM THU-SAT...AND BELOW NORMAL SUNDAY IF THE CLOUDS/PRECIP
MATERIALIZE.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
AT KCLT...THE MVFR CIGS HAVE FINALLY SCATTERED OUT...BUT SOME
CONTINUE TO LINGER TO THE NORTH AND WEST OF THE TERMINAL THIS AFTN.
LOW VFR CLOUDS WILL CONTINUE THRU THE AFTN. THEN MVFR CIG  RETURN BY
EARLY EVENING. LIGHT RAIN IS EXPECTED TO DEVELOP TONIGHT AS A
SURFACE LOW MOVES UP THE COAST. IFR CIGS AND MVFR VSBY EXPECTED WITH
THE PRECIP. RAIN WILL TAPER OFF BY LATE MONDAY MORNING...BUT LOW
CLOUDS AND DRIZZLE WILL LINGER THRU AT LEAST MIDDAY. WINDS ARE
EXPECTED TO FAVOR THE NE THRU THE PERIOD...AS WEAK COLD AIR DAMMING
REGIME DOMINATES.

ELSEWHERE...CIGS HAVE BEEN VARIABLE ACRS THE REGION TODAY...AND IT
WILL PROBABLY CONTINUE THAT WAY THRU THE REST OF THE AFTN...PER
SATELLITE TRENDS. GENERALLY MVFR TO OCCASIONAL VFR CONDITIONS
EXPECTED. THEN CONDITIONS WILL DETERIORATE THIS EVENING...AS
MOISTURE AND PRECIP MOVES IN FROM THE SOUTHWEST...AS A SFC LOW MOVES
UP THE COAST. CIGS ARE EXPECTED TO GO TO IFR...WITH SOME VSBY
RESTRICTIONS POSSIBLE UNDER -RA AND DZ. THE LIGHT RAIN WILL TAPER OFF
MONDAY MORNING...BUT AREAS OF -DZ WILL LIKELY LINGER THRU AT LEAST
MIDDAY...ESP ACRS THE UPSTATE. WINDS WILL CONTINUE IN THE USUAL COLD
AIR DAMMING PATTERN...WITH LIGHT NE WINDS EAST OF THE MTNS AND SE AT
KAVL.

OUTLOOK...LINGERING LOW LEVEL MOISTURE IS LIKELY TO KEEP LOW STRATUS
AROUND THRU MONDAY. A COLD FRONT WILL APPROACH ON TUESDAY FROM THE
WEST AND MOVE THROUGH ON WED. WIDESPREAD SHOWERS WITH RESTRICTIONS
SHOULD ARRIVE TUESDAY AFTERNOON AND WILL CONTINUE UNTIL THE FRONT
CLEARS THE AREA LATE WEDNESDAY.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       HIGH 100%     MED   72%     LOW   54%     MED   78%
KGSP       HIGH  94%     LOW   54%     MED   73%     HIGH  81%
KAVL       HIGH  80%     HIGH  87%     MED   76%     HIGH  87%
KHKY       HIGH  98%     HIGH  82%     MED   72%     HIGH  85%
KGMU       HIGH  96%     LOW   58%     MED   73%     HIGH  81%
KAND       HIGH  92%     LOW   46%     MED   67%     HIGH  87%

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...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...SBK
NEAR TERM...ARK
SHORT TERM...JOH
LONG TERM...WIMBERLEY
AVIATION...ARK





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