Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 270547
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1247 AM EST SAT DEC 27 2014

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE CAROLINA COAST TONIGHT AND
SATURDAY AS A COLD FRONT APPROACHES FROM THE WEST.  EXPECT
TEMPERATURES TO BE A FEW DEGREES ABOVE NORMAL THIS WEEKEND.  THE
FRONT WILL CROSS MONDAY WITH A SECONDARY FRONT PASSING IN MID WEEK
DROPPING TEMPERATURES TO BELOW NORMAL. THE NEXT COLD FRONT WILL
ARRIVE AT THE END OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1245 AM...PATCHY/MAINLY THIN CIRRUS WILL CONTINUE TO STREAM
OVER THE AREA THROUGH THE OVERNIGHT...BUT THE BALANCE OF THE NIGHT
SHOULD BE NO WORSE THAN PARTLY CLOUDY. SOME PATCHY FOG...MAINLY
GROUND FOG WILL BE POSSIBLE TOWARD MORNING ACROSS THE PIEDMONT AND
MTN VALLEYS...WHILE MIN TEMPS WILL BE VERY CLOSE TO CLIMO.

AS OF 1010 PM...THE AXIS OF A MID LEVEL RIDGE HAS DRIFTED EAST
THROUGH THIS EVENING. ON THE WEST SIDE OF THE RIDGE...HIGH AND MID
LEVEL CLOUDS HAVE INCREASED ACROSS THE SOUTHERN APPALACHIAN REGION.
I WILL UPDATE THE SKY FORECAST TO ALIGN WITH SATELLITE OBSERVATIONS.
TEMPS AND DEWPOINTS TRENDS APPEAR IN GOOD SHAPE.

AS OF 650 PM...FORECAST REMAINS IN GOOD SHAPE. PATCHES OF HIGH
CLOUDS WILL STREAM NE ACROSS THE SOUTHERN APPALACHIAN REGION...AS
THE H5 RIDGE AXIS SLIDES EAST. SFC HIGH PRESSURE IS EXPECTED TO
REMAIN ACROSS THE REGION...YIELDING LIGHT TO CALM WINDS. I WILL
UPDATE HOURLY GRIDS TO ALIGN WITH OBS.

AS OF 450 PM...LATEST SATELLITE IMAGES INDICATED A FEW PATCHES OF
HIGH CLOUDS DRIFTING ACROSS THE WESTERN CAROLINAS LATE THIS
AFTERNOON. I WILL UPDATE THE FORECAST TO ALIGN HOURLY TEMP/DWPTS TO
OBSERVATIONS AND ADJUST SKY COVER. OTHERWISE...THE CURRENT FORECAST
REMAINS ON TRACK.

AS OF 200 PM EST FRIDAY...DEEP MOISTURE ASSOCIATED WITH A WEAK UPPER
DISTURBANCE CURRENTLY OVER THE NORTHERN AL/TN IS EXPECTED TO LIFT
NEWARD...PASSING WEST OF THE SOUTHERN APPALACHIANS THROUGH TONIGHT.
THIS WILL BRING CONSIDERABLE HIGH CLOUDS TO THE WESTERN MTNS ZONES
THROUGH THE EVENING HOURS. OTHERWISE...WE WILL SEE CONTINUED DRY
WEATHER WITH MOSTLY CLEAR SKIES AS AN UPPER RIDGE CONTINUES TO
AMPLIFY ACROSS THE SOUTHEAST STATES AND A SURFACE HIGH REMAINS IN
PLACE. WITH INCREASING THICKNESSES AND PREVAILING WEAK SOUTHERLY
WINDS...MORNING LOW TEMPS ON SAT WILL BE AROUND 2-3 DEGREES WARMER
THAN THIS MORNING/S LOW.

SAT...MOIST SWLY FLOW DEVELOPS ACROSS THE AREA AS THE UPPER RIDGE
AXIS MOVES OFFSHORE AND AN UPPER TROUGH MOVES EAST ACROSS THE
ROCKIES. THIS WILL ALLOW SURFACE HIGH TO MIGRATE OFF THE EAST COAST
AND A SURFACE COLD FRONT TO MOVE EASTWARD INTO THE MISSISSIPPI
VALLEY  THROUGH SAT AFTERNOON. LATEST MODELS CONTINUE TO SUGGEST
THAT A WAVE OF LOW WILL DEVELOP OVER THE WESTERN GULF AND LIFT NE
ALONG THE FRONT THRU SAT EVENING. THIS WILL DRAW A DEEP PLUME OF
GULF MOISTURE INTO THE SOUTHEAST. HOWEVER...MODELS HAVE TRENDED A
BIT SLOWER WITH THE ONSET OF PRECIP...KEEPING OUR CWA DRY UNTIL 00Z
SUN. HENCE...HAVE GONE WITH DRY FORECAST THRU SAT EVENING. PARTLY
CLOUDY SKIES SAT MORNING WILL GIVE WAY TO MOSTLY CLOUDY BY SAT
EVENING IN LIGHT OF INCREASING MOISTURE. AFTERNOON TEMPS WILL STAY
7-10 DEGREES ABOVE CLIMO FOR MOST LOCATIONS.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
AS OF 230 PM FRI...HOPE YOU MADE THE MOST OF THE SUNSHINE TODAY AND
WILL MAKE THE BEST OF IT ON SATURDAY...BECAUSE IT LOOKS LIKE WE ARE
IN FOR ANOTHER PERIOD OF CLOUDY AND WET WEATHER STARTING SATURDAY
NIGHT. THE MODELS ARE IN GOOD AGREEMENT WITH SPREADING FORCING AND
DEEP MOISTURE INTO THE REGION FROM THE SOUTHWEST STARTING ON
SATURDAY EVENING. THAT SAID...THE MODELS ALSO INDICATE A DELAY WITH
THE ONSET OF THE PRECIP RELATIVE TO THE OLD FORECAST. SOME MID LEVEL
FORCING SHOULD ARRIVE VERY LATE IN THE DAY...AS A LEAD WAVE COMES UP
FROM THE SW AND MID LEVEL ISENTROPIC UPGLIDE COMMENCES...BUT THAT
WILL PROBABLY NOT BE ENOUGH TO GET THE PRECIP DOWN TO THE GROUND
UNTIL AFTER 00Z SUNDAY WITH AN EXPECTED DRY SUBCLOUD LAYER TO
OVERCOME. SO...THE TIMING OF ONSET HAS BEEN NARROWED TO INDICATE A
DELAY THEN MORE RAPID RAMP UP OF HIGH PRECIP PROBABILITY...
ESPECIALLY OVER THE WRN PIEDMONT OF NC. THE NEW FCST EVENTUALLY
CATCHES UP TO THE OLD FCST BY SUNRISE ON SUNDAY WITH A
CATEGORICAL POP OVER THE WEST AND A LIKELY POP OVER THE EAST. FROM
THAT POINT ONWARD...THE MODELS KEEP DEEP MOISTURE AND SOME MANNER
OF FORCING OVER THE REGION INTO MONDAY...BE IT UPPER DIVERGENCE
SUNDAY MORNING...MID LEVEL DPVA SUNDAY AND SUNDAY NIGHT...OR MOIST
UPGLIDE THROUGHOUT THAT PERIOD. THE FCST KEEPS A FAIRLY HIGH
POP...FAVORING THE MTNS A BIT THROUGH SUNDAY NIGHT. THE PASSAGE OF
THE MAIN SHORT WAVE AXIS EARLY MONDAY SHOULD BRING AN END TO THE
BETTER CHANCES OF PRECIP. FROM THAT POINT ONWARD...A SLOW DECREASE
IN COVERAGE ON MONDAY. WE SHOULD DRY OUT BY SUNRISE ON TUESDAY.
FORTUNATELY...TEMPS WILL REMAIN ABOVE FREEZING THROUGH THE WHOLE
PERIOD...SO NO PRECIP TYPE ISSUES ARE EXPECTED AT THIS TIME.
UNLIKE PREVIOUS EVENTS...THE CENTER OF HIGH PRESSURE TO OUR EAST
CLOSER TO BERMUDA SHOULD ALLOW US TO REMAIN UN-WEDGED. EVEN MORE
FORTUNATELY...THE MODELS FAIL TO DEVELOP ANY INSTABILITY ACROSS
THE REGION...SO SEVERE WEATHER CHANCES LOOK VERY LOW IN SPITE OF
BEING FREE FROM COLD AIR DAMMING.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 215 PM FRIDAY...MODELS ARE COMING INTO A LITTLE BETTER
AGREEMENT ON THE MEDIUM RANGE FORECAST. TUESDAY THRU THURSDAY STILL
LOOKS DRY AND SEASONABLY COOL...AS A LARGE MODIFYING ARCTIC AIR MASS
SETTLES ACRS THE MID SECTION OF THE COUNTRY UNDER CONFLUENT SPLIT
FLOW ALOFT. A CUTOFF LOW INVOF CALIFORNIA WILL EVENTUALLY GET KICKED
OUT INTO THE SOUTHERN STREAM...AT SOME POINT LATE NEXT WEEK. MODELS
CONTINUE TO DELAY THE TIMING OF THIS SHORTWAVE TROF. USING THE
LATEST CONSENSUS...I HAVE DELAYED POPS RETURNING UNTIL FRIDAY
MORNING. WITH A COLD AIR MASS STILL IN PLACE WHEN THE MOISTURE FIRST
STARTS ADVECTING BACK IN FROM THE SOUTHWEST...THERE MAY BE SOME P-
TYPE CONCERNS. HOWEVER...THERE IS STILL A LOT OF UNCERTAINTY ON THE
EXACT TIMING. ALSO...REGARDLESS OF THE MODEL SOLN...IT DOES LOOK
LIKE LLVL THICKNESSES WILL INCREASE AS PRECIP MOVES IN...SUCH THAT
PRECIP SHUD CHANGE OVER TO ALL RAIN. BOTH THE GFS AND ECMWF HAVE
ONLY A WEAK IN SITU COLD AIR DAMMING WEDGE ACRS THE CWFA BY FRIDAY
NIGHT. HIGH TEMPS WILL CONTINUE TO BE SLIGHTLY BELOW NORMAL THRU
FRIDAY...WITH NEAR TO SLIGHTLY ABOVE NORMAL LOWS.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS ARE EXPECTED FOR AT LEAST THE
NEXT 18 HOURS. CANNOT COMPLETELY RULE OUT SOME GROUND FOG CAUSING
REDUCED VISBY (ACCORDING TO ASOS)...ESP AT KAVL AND THE UPSTATE SC
TERMINALS...BUT ANY IMPACT ON AVIATION WOULD BE MINIMAL. OTHERWISE...
CALM OR LIGHT/VRBL WINDS WITH VARYING MID/HIGH LEVEL CLOUDS WILL BE
SEEN UNTIL SATURDAY AFTERNOON...WHEN LIGHT SOUTH WINDS SHOULD
DEVELOP AND MID/HIGH CIGS SHOULD BEGIN TO THICKEN UP A BIT. BY THE
END OF THE PERIOD...-RA MAY BE FALLING AT THE WESTERN-MOST TERMINALS
IN ADVANCE OF AN APPROACHING COLD FRONT...WHILE MVFR CIGS APPEAR
LIKELY AT KAVL BY LATE SAT EVENING.

OUTLOOK...PERIODS OF RAIN AND FLIGHT RESTRICTIONS ARE EXPECTED
THROUGHOUT SUNDAY INTO MONDAY...BEFORE GRADUAL IMPROVEMENT OCCURS
MONDAY AND MONDAY NIGHT. DRY HIGH PRESSURE SHOULD RETURN BY MID-
WEEK.

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   75%     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...DEO
NEAR TERM...JDL/NED
SHORT TERM...PM
LONG TERM...ARK
AVIATION...JDL



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