Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 172103
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
403 PM EST WED DEC 17 2014

.SYNOPSIS...
WEAK HIGH PRESSURE WILL LINGER THROUGH TONIGHT. THEN 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 THURSDAY/...
400 PM UPDATE...FCST MAINLY ON TRACK BUT SEE AN OPPORTUNITY TO
REDUCE SKY COVER LATE THIS AFTN AS MORE WIDESPREAD CIRRUS REMAIN OFF
TO OUR WEST. STILL WILL EXPECT THESE TO SPREAD E ACRS THE AREA BY
EVENING. WILL PUBLISH NEW GRIDS AFTER TOUCHING UP TEMPS WITH 4 PM
OBS.

AS OF 200 PM EST WEDNESDAY...DRY 1026MB SURFACE HIGH CENTERED OVER
KY/TN WILL CONTINUE TO RIDGE INTO THE FORECAST AREA...RESULTING IN
PREDOMINANT NW FLOW AND DRY CONDITIONS THIS EVENING INTO TONIGHT.
MOSTLY CLEAR SKIES THIS EVENING WILL GIVE WAY TO INCREASING HIGH
CLOUDS BY LATE TONIGHT AS A WEAK UPPER SHORTWAVE APPROACHES FROM THE
MID-MISSISSIPPI VALLEY.  WITH THE COMBINATION OF DOWNSLOPE EFFECT
AND WEAK CAA FLOW...OVERNIGHT LOWS WILL STAY AROUND 2-3 DEGREES
ABOVE NORMAL OVER THE PIEDMONT. AREAS OVER THE MTNS/VALLEYS WILL SEE
SEASONABLY COLD OVERNIGHT TEMPS.

THURSDAY...MOISTURE ASSOCIATED WITH THE UPPER SHORTWAVE WILL
APPROACH FROM THE WEST...REACHING THE SOUTHERN APPALACHIANS BY
MID-DAY. LATEST SHORT RANGE MODELS HAVE BACKED OFF ON THE PRECIP
OVER THE TN BORDERLINE AS THE BEST UPPER FORCING PASSES NORTH OF THE
AREA AND MOIST LAYER REMAINS ELEVATED. NEVERTHELESS...WITH THE HELP
OF NW UPSLOPE FLOW...CAN NOT RULE OUT PERIODS OF LIGHT PRECIP
DURING THE EARLY AFTERNOON HOURS. HENCE...HAVE INHERITED SLIGHT
CHANCE POPS FOR RAIN AND SNOW SHOWERS MAINLY OVER THE TN BORDERLINE.
CONDITIONS SHOULD DRY OUT AS THE UPPER WAVE PUSHES FARTHER NE.
ELSEWHERE WILL SEE CONTINUED DRY CONDITIONS WITH PARTLY TO MOSTLY
CLOUDY SKIES. AFTERNOON HIGHS WILL RUN NEAR NORMAL FOR MOST
LOCATIONS.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 245 PM WEDNESDAY...THE WEAK UPR WAVE WILL QUICKLY DRIFT EAST
OF THE CENTRAL APPALACHIANS THURSDAY NIGHT...WHILE LLVL FLOW REMAINS
W/NWLY. OTHER THAN LINGERING CLOUDS...EXPECT QUIET WX CONDITIONS
WITH TEMPS DIPPING INTO THE 20S TO MID 30S IN THE MTNS...AND MID-UPR
30S IN THE PIEDMONT.

FRIDAY...A POTENT SRN STREAM SHORTWAVE TROF WILL ENTER THE LWR MS
VLY...WHILE SFC HIGH PRES (~1030MB) WILL SLIDE INTO THE GREAT LAKES.
MODEL MOISTURE PROFILES INDICATE VARIABLE CLOUDINESS ACRS THE
CWFA...WITH W/NWLY UPSLOPE LOW CLOUDS LIKELY TO PERSIST ALONG THE TN
BORDER. TEMPS WILL BE NEAR NORMAL EAST OF THE MTNS...BUT BELOW
NORMAL IN THE HIGH TERRAIN THANKS TO MORE CLOUDS AND PERSISTENT NWLY
CAA FLOW.

FRIDAY NIGHT AND SATURDAY...MODELS ARE IN REASONABLE AGREEMENT ON
THE TIMING AND FORCING ASSOCIATED WITH THE SRN STREAM MID-UPR
WAVE...MAXIMIZING Q-VECTOR CONVERGENCE AROUND 12Z SAT.
MEANWHILE...COLD AIR DAMMING WILL SET UP...AS 1028-1030MB SFC HIGH
CROSSES QUEBEC...AND MOIST UPGLIDE BREAKS OUT ACRS THE REGION.
PRECIP RAMPS UP FROM SW TO NE LATE FRIDAY NGT TO MIDDAY SATURDAY TO
CATEGORICAL. QPF AMOUNTS SHUD BE GENERALLY 0.5" OR LESS. ALTHO...THE
NAM IS A WET OUTLIER...WITH WIDESPREAD AREAS RECEIVING MORE THAN
0.5". THE BIGGEST CONCERN WITH THIS SYSTEM WILL BE THE P-TYPE...AS
MODELS CONTINUE TO AGREE ON ENUF COOL LLVL AIR/THICKNESSES ACRS THE
NC MTNS TO SUPPORT A WINTRY MIX. AS USUAL...THE NAM AND GFS FCST
SNDGS STILL DISAGREE ON THE EXTENT/MAGNITUDE OF A WARM NOSE...AND
THE DEPTH OF A WARM SFC LAYER. GIVEN THE HYBRID CAD WITH GOOD
UPSLOPE AND LLVL CAA...I LEANED TOWARD THE NAM (GOING 2/1 NAM/GFS).
THIS RESULTS IN MOSTLY A SLEET/SNOW MIX...WITH OCCASIONAL PATCHY ICE
DURING THE ONSET EARLY SAT MORNING. GIVEN THE EXPECTED QPF...I THINK
IT IS REASONABLE FOR THERE TO BE 2-4 INCHES OF A SLEET/SNOW MIX ACRS
THE NRN MTNS AND ADJACENT ESCARPMENT...POSSIBLY TO THE BLACK MTNS.
FURTHER SOUTH...IT/S MORE UNCERTAIN. SO WITH ALL THAT SAID...IT
STILL LOOKS LIKE AN ADVISORY LEVEL EVENT. HOWEVER...IF THE COLD AIR
IS DEEP ENUF (PER NAM)...ENUF SLEET MAY ACCUM TO MAKE THIS A LOW-END
WARNING EVENT FOR PORTIONS OF THE NRN NC ESCARPMENT. I USED THE
CONSENSUS OF RAW MODEL TEMPS FOR THESE PERIODS...WHICH IS THE
COLDEST GUIDANCE AVAILABLE...DUE TO THE WEDGE. TEMPS WILL HOVER IN
THE 30S TO LWR 40S FOR MOST OF THE AREA.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...ANOTHER DEEP SRN STREAM SHORTWAVE TROF WILL
DIG ACRS NRN MEXICO AND SRN PLAINS SATURDAY NIGHT THRU SUNDAY...THEN
IS EXPECTED TO PHASE WITH THE NORTHERN STREAM SUNDAY NGT THRU
WEDNESDAY...DEVELOPING INTO A DEEP CLOSED UPR LOW. THE 12Z GFS AND
ECMWF HAVE COME INTO A LITTLE BETTER AGREEMENT WITH THIS
PATTERN...BUT STILL DIFFER ON THE EXACT POSITION/DEPTH OF THE CLOSED
LOW...AND THE TIMING OF ASSOCIATED SFC WAVES TO AFFECT OUR CWFA.
GOING WITH A SUPERBLEND OF CONS/WPC/OFFICIAL...THERE IS A LINGERING
SLGT CHC TO LOW-END CHC POP THRU MUCH OF THE PERIOD FROM SAT NGT
THRU TUE...WITH NEAR NORMAL TEMPS. IF THERE ARE SUB-FREEZING TEMPS
IN THE MTNS ANY OF THOSE NIGHTS...THERE MAY BE SOME PATCHY FREEZING
RA/DZ...GIVEN THE LACK OF ICE NUCLEI ACTIVATION. HOWEVER...I AM NOT
THAT CONFIDENT ON THAT. IT DOES LOOK TO BE FAIRLY CLOUDY
HOWEVER...AS COLD AIR DAMMING CONTINUES SUNDAY/MONDAY...WITH A WEAK
COASTAL LOW TO OUR SE. TUESDAY MAY BE A MORE PLEASANT DAY...WITH
SOME SUNSHINE (IF MODELS CONTINUE TO SLOW DOWN THE NEXT SYSTEM).

TUESDAY AND WEDNESDAY...THE GFS IS STILL ABOUT 12 HOURS FASTER THAN
THE ECMWF ON A STRONG COLD FRONTAL PASSAGE...WITH THE ECMWF STILL
SHOWING A 12Z WEDNESDAY FROPA. THE ECMWF...WITH ITS STRONGER/DEEPER
MID-UPR LOW...HAS VERY STRONG FLOW WITH THE FRONT...WITH 850 MB FLOW
OF 50-60+ KTS ON BOTH THE WAA AND CAA SIDE OF THE SYSTEM. SO THERE
MAY BE A THREAT FOR HEAVY RAIN...SEVERE WX AND/OR WINTRY PRECIP
AROUND DEC 23-24. STILL NEED MORE TIME TO IRON OUT THE DETAILS...BUT
ALREADY HAVE LIKELY POPS TUESDAY NIGHT (WHICH IS DAY 7). TEMPS LOOK
TO BE NEAR OR ABOVE NORMAL AHEAD OF THE FRONT...AND TOO WARM FOR
WINTRY PRECIP...BUT THEN WRAP AROUND MOISTURE WITH PLUMMETING
THICKNESSES SHUD RESULT IN SNOW IN THE MTNS BY WEDNESDAY NIGHT.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD FOR ALL TERMINALS AS HIGH PRESSURE CONTINUES TO BUILD IN FROM
THE WEST. SW TO NW WINDS THIS AFTERNOON WILL DECREASE AND VEER
OVERNIGHT...ENDING UP NE BY EARLY THU MORNING. THE EXCEPTION WILL BE
KAVL WHERE GUSTY N WINDS OF 15-20 KTS WILL CONTINUE THROUGH THIS
AFTERNOON BEFORE DECREASING TO AROUND 5-7 KTS OUT OF THE NORTH BY
THIS EVENING. SKIES WILL REMAIN MOSTLY CLEAR THROUGH TONIGHT...WITH
HIGH CLOUDS OVERSPREADING THE REGION BY EARLY TOMORROW MORNING AS AN
UPPER SHORTWAVE PASSES NORTH OF THE AREA.

OUTLOOK...A WEAK UPPER DISTURBANCE WILL SLIDE THROUGH THE REGION ON
THURSDAY WITH LITTLE/NO IMPACT EXPECTED.  ANOTHER MORE ORGANIZED
SYSTEM WILL APPROACH FROM THE WEST FOR THE START OF THE WEEKEND 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...

            21-03Z        03-09Z        09-15Z        15-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     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...NONE.
NC...NONE.
SC...NONE.

&&

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



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