Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 162044
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
344 PM EST TUE DEC 16 2014

.SYNOPSIS...
HIGH PRESSURE WILL SPREAD BACK OVER THE REGION WEDNESDAY BEHIND A
DEPARTING COLD FRONT. A WEAK WEATHER SYSTEM ALOFT WILL SPREAD CLOUDS
AND PERHAPS SOME SPOTTY LIGHT SHOWERS IN THE MOUNTAINS ON THURSDAY.
ANOTHER LOW WILL DEVELOP TO OUR SOUTHWEST ON FRIDAY AND INCREASE
CHANCES FOR WIDESPREAD PRECIPITATION GOING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
2045 UTC UPDATE...SKY COVER AND POPS HAVE BEEN REDUCED EAST OF THE
BLUE RIDGE PER SATELLITE AND RADAR TRENDS.

AS OF 200 PM EST TUESDAY...THIS AFTERNOON THROUGH TONIGHT...A COLD
FRONT WAS CROSSING OUR WESTERN ZONES OF THE MTNS...WITH GUSTY WSW/SW
WAA WINDS PERSISTING MAINLY EAST OF THE MTNS AHEAD OF THE FRONT AS
OF EARLY AFTERNOON HOURS. LLVL CLOUDS CURRENTLY OVER THE WESTERN NC
PIEDMONT SHOULD SCATTER OUT SOON AS DRY AIRMASS OVERSPREADS FROM THE
WEST PER LATEST SATELLITE IMAGERY TREND. MEANWHILE...LOW CLOUDS WERE
OVERSPREADING ACROSS THE SOUTHERN APPALACHIANS BEHIND THE FRONT.

MODELS AGREE THAT THE FRONT WILL CROSS THE REGION THROUGH THIS
EVENING AND WINDS SHOULD DECREASE AND VEER TO THE NW IN ITS WAKE.
THE CROSS SECTION OF THE NAM EXTENDING FROM THE NORTH NC MTNS TO THE
LOWER NC PIEDMONT DEPICTS RATHER SHALLOW LLVL MOIST LAYER (SURFACE
TO 800MB) OVER THE NW FACING SLOPES OF THE APPALACHIANS...WITH
PREVAILING NW UPSLOPE FLOW THIS EVENING INTO MID-NIGHT. THE MOIST
LAYER WILL BECOME SHALLOWER THROUGH TOMORROW MORNING WITH WINDS
VEERING TO LESS FAVORABLE WSWLY. THEREFORE...HAVE INHERITED SLIGHT
CHANCE TO LOW END CHANCE FOR SNOW SHOWERS OVER THE HIGHER PEAKS WITH
RAIN/SNOW MIX OVER THE LOWER VALLEYS THIS EVENING THRU
TONIGHT...TAPERING OFF TOWARDS TOMORROW MORNING. SNOW ACCUMS APPEAR
TO BE ON THE LOW SIDE...WITH LESS THAN AN INCH OVER THE HIGHER
ELEVATIONS. ELSEWHERE WILL SEE CONTINUED DRY CONDITIONS AS DRY HIGH
PRESSURE BUILDS IN FROM THE WEST. DESPITE THE FROPA...OVERNIGHT
TEMPS WILL BE NEAR...OR A FEW DEGREES ABOVE NORMAL.

TOMORROW...DRY AND NORMAL TEMPS ARE EXPECTED AS DRY 1025MB HIGH
PRESSURE CENTERED OVER THE UPPER MISSISSIPPI VALLEY CONTINUES TO
RIDGE SOUTHEASTWARD INTO THE FORECAST AREA. THE MAIN ISSUE WILL BE
EARLY MORNING PATCHY FOG MAINLY OVER THE EXTREME WESTERN NC VALLEYS
AND UPSTATE SC WHERE MODEL SOUNDINGS SHOW CALM CONDITIONS AND VERY
LOW DEW-POINT DEPRESSION UNDER LLVL INVERSION LAYER. AFTERNOON TEMPS
WILL REMAIN NEAR OR A FEW DEGREES ABOVE NORMAL FOR MOST LOCATIONS.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 145 PM TUESDAY...THE SHORT TERM PERIOD OF THE FORECAST WILL BE
QUIET AS GENERALLY ZONAL FLOW ALOFT PREVAILS ACROSS THE REGION. A
MINOR SHORT WAVE WILL QUICKLY MOVE ACROSS THE AREA ON THURSDAY.
HOWEVER...THIS FEATURE CONTINUES TO LACK ANY MOISTURE FLUX SO ANY
MEASURABLE PRECIPITATION IS DOUBTFUL. ABOUT THE MOST THAT SHOULD BE
EXPECTED IS FOR AN INCREASE IN CLOUDINESS WITH MAYBE SOME SPRINKLES
IN THE MOUNTAINS. WEAK UPPER RIDGING IS FORECAST ON FRIDAY AS A
SOUTHERN STREAM WAVE REACHES THE LOWER MISSISSIPPI VALLEY BY LATE IN
THE DAY. CLOUDINESS SHOULD BE ON THE INCREASE FRIDAY AFTERNOON AS
ISENTROPIC LIFT BEGINS. MAX TEMPS SHOULD BE HELD IN CHECK BY PERIODS
OF CLOUD COVER...BUT NOT FAR FROM CLIMO.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 215 PM EST TUESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
SATURDAY WITH A SOUTHERN STREAM UPPER TROF APPROACHING THE FCST AREA
FROM THE WEST. THE LONG MODELS ARE COMING INTO BETTER AGREEMENT WRT
THE EVOLUTION OF THE TROF AND ITS TIMING. BOTH THE LATEST 12Z GFS
AND OLDER 00Z ECMWF HAVE THE SYSTEM TAKING ON A MORE NEGATIVE TILT
AS IT MOVES OVER THE FCST AREA LATE SAT/EARLY SUN WITH THE ECMWF
STILL MORE AMPLIFIED OVERALL. AFTER THE TROF LIFTS NE ON SUN...MORE
ZONAL UPPER FLOW SETTLES OVER THE REGION WHILE THE NEXT TROF DIGS
DOWN OVER THE SW CONUS. ITS LOOKING LIKE THIS SYSTEM WILL GRADUALLY
APPROACH THE CWFA OVER THE NEXT FEW DAYS AND WONT LIKELY REACH OUR
AREA UNTIL NEW DAY 7 OR BEYOND.

AT THE SFC...MUCH BETTER CONSISTENCY IS NOW BEING DISPLAYED BETWEEN
THE OPERATIONAL MODELS. THEY ALL DEVELOP A FAIRLY WEAK LOW OVER THE
FAR NORTHERN GULF OF MEXICO ON SAT AND MOVE THE CYCLONE OVER THE
CWFA LATE SAT/EARLY SUN. COMPARED TO PREVIOUS MODEL RUNS...THE ECMWF
HAS A WEAKER LOW OVERALL AND THE GFS HAS A MORE WELL DEFINED SYSTEM
COMPARED TO ITS EARLIER RUNS. THE GFS LOW LVL PROFILES ARE STILL
WARMER ON SAT COMPARED TO THE ECMWF AND IF YOU USED THEM AS IS YOU
WOULD GET RAIN EVERYWHERE EXCEPT THE NORTHERN NC MTS AND MAYBE THE
SOME OF THE CENTRAL NC MTS. I OPTED TO TAKE A BLEND OF THE TWO WHICH
PRODUCES SLIGHTLY WARMER PROFILES OVERALL COMPARED TO THE PREVIOUS
FCST. I USED A PARTIAL THICKNESS BLEND BETWEEN THE GFS AND ECMWF TO
CREATE P-TYPE GRIDS. THIS GAVE ME RAIN EVERYWHERE EXCEPT FOR A
COUPLE TENTHS OF AN INCH OF FZ RAIN OVER THE NORTHERN NC MTS EARLY
SAT. IF THINGS TREND ANY WARMER...IT WILL LIKELY RESULT IN AN ALL
RAIN SCENARIO. THINGS SHOULD DRY OUT FAIRLY QUICKLY EARLY SUN AS
HIGH PRESSURE BUILDS IN THE LOWS WAKE. ANY LINGERING PRECIP WILL
LIKELY BE CONFINED ALONG THE NC/TENN BORDER AREA AND POSSIBLY THE
NORTHERN NC PIEDMONT. POPS INCREASE AGAIN ON TUES AS THE NEXT
FRONTAL SYSTEM APPROACHES THE REGION.

&&

.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
AT KCLT...LATEST SATELLITE IMAGERY TREND SHOWS AREAS OF IFR CLOUDS
SCATTERING OUT FROM THE WEST. THEREFORE...IFR CIGS SHOULD PERSIST
BEFORE LIFTING TO THE VFR LVL BY AROUND 20Z. OTHERWISE...EXPECT VFR
THRU 18Z WED AS A COLD FRONT MOVES ACROSS THE AREA THIS EVENING
FOLLOWED BY DRY HIGH PRESSURE TONIGHT AND TOMORROW. WE WILL SEE
GUSTY SW WINDS OF 15-20 KTS AHEAD OF THE FRONT THIS AFTERNOON. WINDS
WILL DECREASE AND VEER TO THE NW BY 00Z WED AS THE FRONT PUSHES TO
THE EAST. SKIES SHOULD REMAIN MOSTLY CLEAR THIS EVENING INTO WED
AFTERNOON.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH A MIXTURE OF VFR/MVFR
IMPROVING TO VFR THIS AFTERNOON AS DRY AIRMASS SPREADS FROM THE WEST
AHEAD OF AN APPROACHING FRONT. EXPECT GUSTY SW WINDS OF 15-20KTS TO
CONTINUE THROUGH THIS AFTERNOON BEFORE WINDS DECREASE AND VEER TO
THE NW BY LATE THIS AFTERNOON/EVENING IN LIGHT OF THE FROPA. THE
EXCEPTION WILL BE KAVL WHERE MVFR CLOUDS AND GUSTY N WINDS WILL
PERSIST THROUGHOUT THE TAF CYCLE. ELSEWHERE WILL SEE VFR CONDIIONS
UNDER MOSTLY CLEAR SKIES THROUGH MUCH OF THE PERIOD. HOWEVER...SOME
MODELS SUGGEST THAT DEW PINT DEPRESSION WILL CRASH TOWARD
SUNRISE...PROMOTING THE FORMATION OF IFR/MVFR FOG MAINLY OVER THE
UPSTATE SC AND NORTHEN NC PEIDMONT. HENCE...HAVE MENTIONED TEMPO FOR
IFR/MVFR VISBY FOR THE AFFECTING TERMINALS.

OUTLOOK...DRY HIGH PRESSURE WILL SPILL IN LATE ON TUESDAY BEHIND THE
FROPA...LASTING THROUGH MIDWEEK.  ANOTHER SYSTEM WILL APPROACH FROM
THE WEST NEAR WEEKS END ONCE AGAIN INCREASING PRECIP/RESTRICTION
CHANCES.  SOME WINTRY PRECIP IS POSSIBLE ACROSS THE NC
MOUNTAINS/FOOTHILLS AFFECTING BOTH KAVL AND KAND SATURDAY MORNING.
WINTRY PRECIP IS NOT EXPECTED AT THIS TIME FOR ANY OTHER TAF SITES.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       HIGH  90%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH  91%     HIGH 100%
KAVL       HIGH 100%     HIGH  93%     MED   75%     HIGH 100%
KHKY       HIGH  98%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  98%     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...NONE.
NC...NONE.
SC...NONE.

&&

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



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