Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 180541
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1241 AM EST THU DEC 18 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 TODAY/...
AS OF 1235 AM EST THURSDAY...HIGH LEVEL CIRRUS CONTINUES TO STREAM
IN ALOFT FROM UPSTREAM UPPER WAVE THAT IS CURRENTLY SLIDING THROUGH
THE MIDSOUTH.  STILL EXPECTING FURTHER THICKENING OF SKY COVER
OVERNIGHT AS THIS WAVE ADVECTS EAST LEADING INTO MOSTLY CLOUDY SKIES
BY SUNRISE.  TEMPERATURES ACROSS THE REGION CONTINUE TO HOVER IN THE
LOWER/MID 30S ACROSS THE HIGH TERRAIN WITH UPPER 30S TO LOWER 40S
FEATURED ACROSS THE NC/SC PIEDMONT REGIONS.  CURRENT FCST REMAINS ON
TRACK THEREFORE NO CHANGES WERE MADE.

PREVIOUS DISCUSSION...

930 PM UPDATE...TOUCHED UP TEMPS OVER THE NEXT FEW HOURS. SEVERAL
SITES WHERE WINDS HAVE REMAINED UP HAVE STAYED SEVERAL DEGREES
WARMER THAN SURROUNDING AREAS. ONCE THESE SITES BEGIN TO CALM THEIR
TEMPS SHOULD FALL BACK FAIRLY QUICKLY. ALSO ADJUSTED SKY COVER A BIT
PER SATELLITE. SEEING A FEW MTN WAVE CIRRUS OVER VA ATTM WITH A FEW
POSSIBLY STARTING TO FORM OVER NW NC. THE SETUP IS SOMEWHAT
FAVORABLE FURTHER SOUTH...WITH WEAKER UPPER FLOW BEING A LIMITING
FACTOR. NONETHELESS HIT CLOUD COVER A LITTLE HARDER IN THE FOOTHILLS
THRU THE EARLY MRNG.

630 PM UPDATE...NO SIGNIFICANT CHANGES OVERNIGHT. STILL WILL
EXPECT CIRRUS TO INCREASE AND BE JOINED BY MIDLEVEL CLOUDS AS
THE NIGHT GOES ON. TEMP TRENDS LOOK GOOD IN LIGHT OF OBS OVER THE
PAST COUPLE HRS...AND LATEST GUID CONTINUES TO BACK UP MINS NEAR
CLIMO. 18Z NAM/GFS WERE NOT ANY MORE SUPPORTIVE OF QPF IN THE EARLY
PART OF THE DAY THU...SO I BACKED OFF THE ALREADY LOW-END POPS IN
THE SRN MTNS. HOWEVER I DID KEEP A SCHC FOR THE AFTN FURTHER NORTH
WHERE THE INCOMING S/W TROF WILL HAVE MORE OF AN IMPACT. AT THIS
TIME OF DAY EVEN AT THE HIGHER ELEVATIONS TEMPS SHOULD SUPPORT
NEARLY ALL RAIN...WITH NO SNOW ACCUMS EXPECTED.

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 /TONIGHT 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 /06Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD.  ALL TAFS INITIALIZE WITH FEW/SCT HIGH LEVEL CIRRUS.  CIRRUS
WILL THICKEN/LOWER THROUGH MORNING WITH MID LEVEL CIGS FEATURED.  AS
WEAK UPPER WAVE SLIDES BY JUST TO THE NORTH ON THURSDAY...EXPECTING
LOW VFR BKN CIGS TO PREVAIL AT ALL SITES BEFORE SCT OUT INTO THE
EVENING.  WINDS OVERNIGHT WILL REMAIN LIGHT AND NORTHERLY WITH
GRADUAL VEERING TO THE NORTHEAST BY MORNING AT ALL SITES ASIDE FOR
KAVL WHERE WINDS REMAIN NORTHERLY THROUGH THE PERIOD.  WINDS WILL
VEER S/SW AND INCREASE TO 4-7KTS BY LATE MORNING LASTING THROUGH THE
AFTERNOON AT ALL OTHER SITES AS WEAK LEE TROF DEVELOPS.  FLOW WILL
THEN WEAKEN AFTER SUNSET WITH BRIEF NORTHERLY WINDS LEADING INTO A
CALM EVENING AMIDST SCATTERING LOW VFR SKIES.

OUTLOOK...A 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 MTNS AND
FOOTHILLS AFFECTING KAVL/KHKY SATURDAY MORNING. WINTRY PRECIP IS NOT
EXPECTED AT THIS TIME FOR ANY OTHER TAF SITES.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     MED   71%     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...CDG/JOH/WIMBERLEY
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...CDG


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