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Area Forecast Discussion

165
FXUS62 KGSP 220229
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
929 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 920 PM...RAIN IS GRADUALLY FILLING IN ACROSS THE SC MIDLANDS
AND LOWER PIEDMONT AS FORCING IS INCREASING IN RESPONSE TO UPPER AIR
SPEED MAX LIFTING OUT OF THE LOWER MISS VALLEY. BASED UPON CURRENT
RADAR/OBSERVATIONAL TRENDS...IT/S BECOMING MORE CLEAR THAT PRECIP
WILL PRIMARILY AFFECT THE EASTERN HALF OF THE FORECAST AREA...AND
POPS HAVE BEEN SCALED BACK TO CHANCE ACROSS MUCH OF THE WESTERN
THIRD OF THE FORECAST AREA. THIS IS GOOD NEWS REGARDING THE
POTENTIAL FOR EASTERN ESCARPMENT/NORTHERN NC MTN FREEZING
PRECIP...AS IT/S APPEARING MORE LIKELY THAT A COOLING EASTERLY
UPSLOPE FLOW WILL MAKE IT DIFFICULT TO DISLODGE THE SUB-FREEZING
TEMPS WHERE THEY CURRENTLY EXIST. WE STILL CANNOT RULE OUT SOME
-FZRA OR FZDZ...ESPECIALLY ACROSS AVERY COUNTY...SO THE SPECIAL
WEATHER STATEMENT WILL STAND AS IS. OTHERWISE...THE 00Z NAM HAS
PICKED UP ON THE DRIER TREND SUGGESTED BY THE LATEST OBSERVATIONAL
DATA...SO QPF HAS BEEN LOWERED IN ALL AREAS THROUGH THE NIGHT...AS
EVEN AREAS THAT MEASURE WILL LIKELY SEE AROUND A TENTH OF AN INCH
OR LESS.

AS OF 650 PM...-RA HAS BEEN A BIT SLOWER TO MATERIALIZE THAN
PREVIOUSLY ANTICIPATED...BUT IS BEGINNING TO GRADUALLY FILL IN
ACROSS THE LOWER SC PIEDMONT/MIDLANDS AND SRN/CTRL GA. POPS HAVE
BEEN MAINTAINED AT PREVIOUS LEVELS (CATEGORICAL ACROSS THE SOUTHEAST
THIRD...TAPERING TO CHANCE ALONG THE TENN BORDER)...BUT THE ONSET
HAS BEEN DELAYED A COUPLE OF HOURS. OTHERWISE...THE MAIN CONCERN
WILL REVOLVE AROUND THE POTENTIAL FOR -FZRA OR -FZDZ ACROSS THE
NORTHERN MTNS LATER TONIGHT. IT APPEARS THE PRIMARY PROBLEM AREA
WILL ESSENTIALLY BE AVERY COUNTY...WHERE POCKETS OF FREEZING TEMPS
ARE CURRENTLY OBSERVED...AND AN INCREASING EASTERLY UPSLOPE FLOW
WILL LIKELY PROVIDE ENOUGH OF A COOLING MECHANISM TO MAKE IT
DIFFICULT TO DISLODGE THAT COOL AIR OVERNIGHT. THE AREA OF FREEZING
RAIN HAS BEEN INCREASED IN THE GRIDS. HOWEVER...QPF WILL STILL BE
PROBLEMATIC...AS IT/S NO SLAM DUNK THAT THESE AREAS WILL EVEN SEE
MEASURABLE PRECIP. THEREFORE...DO NOT PLAN TO HOIST ANY ADVISORY
ATTM...BUT WILL ISSUE AN SPS TO MENTION THE POTENTIAL FOR A VERY
LIGHT GLAZE...PRIMARILY ON ELEVATED SURFACES.

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 BE SHUNTED
TO THE SOUTH. THEREFORE...HIGH SHEAR LOW CAPE INDUCED SEVERE EVENT
APPEARS UNIMPRESSIVE AT THIS TIME. HAVE INHERITED A CHANCE OF
AFTERNOON THUNDER OVER THE WESTERN NC PIEDMONT...PORTIONS OF THE
UPSTATE SC...NE GEORGIA AND EXTREME WESTERN NC MTN ZONES TO ACCOUNT
FOR THE PRESENCE OF WEAK ELEVATED BUOYANCY. 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 /03Z MONDAY THROUGH FRIDAY/...
AT KCLT...INCREASING LIFT THROUGH A DEEP LAYER OF THE ATMOSPHERE IS
RESULTING IN SLOWLY INCREASING COVERAGE OF -RA ACROSS THE SC
PIEDMONT/MIDLANDS AND CENTRAL GA...WHICH WILL CONTINUE TO EXPAND AS
IT LIFTS NE THROUGH THE NIGHT. -RA AND MVFR CHANCES WILL INCREASE BY
THE END OF THE EVENING...WITH -RA AND/OR -DZ CONTINUING THROUGH MUCH
OF THE MORNING HOURS. FLT CATEGORY WILL GRADUALLY LOWER TO IFR
DURING THE PRE-DAWN HOURS. ONCE THIS OCCURS...CONDITIONS WILL BE
SLOW TO IMPROVE...AS COOL AIR WEDGE IS EXPECTED TO REMAIN LOCKED IN
NEAR THE SURFACE THROUGH MUCH OF THE PERIOD. WINDS SHOULD REMAIN NE
AT 5-10 KTS THROUGH THE PERIOD.

ELSEWHERE...MVFR CONDITIONS CONTINUE AT MOST TERMINALS THIS
EVENING...AND THIS IS LIKELY AS HIGH AS CIGS WILL BE OVER THE NEXT
24 HOURS. INCREASING LIFT THROUGH A DEEP LAYER OF THE ATMOSPHERE IS
RESULTING IN SLOWLY INCREASING COVERAGE OF -RA ACROSS THE SC
PIEDMONT/MIDLANDS AND CENTRAL GA...WHICH WILL CONTINUE TO EXPAND AS
IT LIFTS NE THROUGH THE NIGHT. CHANCES FOR IFR CIGS WILL INCREASE
ACROSS THE AREA BY 06Z...AND A TEMPO FOR IFR HAS BEEN INCLUDED AT
ALL TERMINALS AROUND THIS TIME...WITH IFR CIGS EXPECTED TO SETTLE IN
NO LATER THAN 07Z OR 08Z. ONCE THIS OCCURS...CONDITIONS WILL BE SLOW
TO IMPROVE...AS COOL AIR WEDGE IS EXPECTED TO REMAIN LOCKED IN NEAR
THE SURFACE THROUGH MUCH OF THE PERIOD.

OUTLOOK...WITH LOW LEVEL MOISTURE LOCKED IN PLACE...FLT RESTRICTIONS
OF SOME SORT WILL LINGER THROUGH AT LEAST EARLY TUESDAY. 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. DRY HIGH PRESSURE WILL RETURN LATE WED.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH  98%     LOW   48%     MED   63%     HIGH 100%
KGSP       MED   78%     MED   63%     MED   72%     HIGH 100%
KAVL       HIGH 100%     HIGH  82%     MED   71%     HIGH 100%
KHKY       MED   79%     LOW   55%     MED   68%     HIGH 100%
KGMU       MED   76%     MED   71%     MED   72%     HIGH 100%
KAND       MED   61%     LOW   44%     HIGH  84%     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...NONE.
NC...NONE.
SC...NONE.

&&

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



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