000
FXUS62 KGSP 192348
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
648 PM EST THU DEC 19 2013

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE REGION TONIGHT THROUGH FRIDAY AND
THEN MOVE OFF THE COAST ON SATURDAY. A COLD FRONT WILL APPROACH THE
SOUTHERN APPALACHIANS FROM THE MISSISSIPPI VALLEY ON SATURDAY NIGHT
AND CROSSES THE WESTERN CAROLINAS AND NORTHEAST GEORGIA ON SUNDAY. A
COLD CANADIAN HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST ON
MONDAY AND REMAIN IN PLACE THROUGH MID WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 645 PM...LATEST SATELLITE INDICATED THAT UPSTREAM HIGH CLOUDS
HAVE INCREASED ACROSS THE DEEP SOUTH TO THE MID MISSISSIPPI RIVER
VALLEY. I WILL UPDATE THE FORECAST TO INCREASE SKY GRIDS THROUGH
TONIGHT. OVERALL...THE CURRENT FORECAST IS IN GOOD SHAPE.

AS OF 430 PM...PATCHES OF THICK CIRRUS WILL LIKELY CONTINUE TO DRIFT
ACROSS THE CWA THROUGH THIS EVENING AND OVERNIGHT. I WILL UPDATE THE
FORECAST TO INCREASE SKY COVER. THE CURRENT MIN TEMPERATURE FORECAST
IS A LITTLE WARMER THAT 12Z GUIDANCE. GIVEN THE CURRENT AND EXPECTED
CLOUD COVER...IT APPEARS THAT A WARMER FORECAST WILL VERIFY THE
CLOSEST TO REALITY.

AS OF 200 PM...PLENTY OF THICKENING CIRRUS CONTINUES TO STREAM IN
ATOP A FAIRLY FLAT UPR RIDGE THIS AFTN...AND WILL CONTINUE INTO THIS
EVENING. MEANWHILE...LARGE AREA OF SFC HIGH PRES REMAINS ANCHORED
ACRS THE SOUTHEAST STATES. THE AIR MASS IS VERY DRY...WITH DEWPTS
MIXING INTO THE TEENS TO LOWER 20S...RESULTING IN ALL METARS
REPORTING RH VALUES BELOW 25 PCT. THE MIXING IS ALSO TAPPING INTO A
LITTLE MORE WIND THAN WAS EXPECTED...WITH MANY SITES ACRS THE NC
PIEDMONT REPORTING SOME LOW-END GUSTS. OTHERWISE...PLEASANT WX WILL
CONTINUE INTO THE EVENING. OVERNIGHT TEMPS WILL DROP INTO THE 30S TO
LOWER 40S...WHICH IS ABOVE NORMAL...UNDER MAINLY CIRRUS.

FRIDAY...LARGE DEEP LAYER ANTICYCLONE WILL REMAIN ACRS THE SOUTHEAST
STATES...WITH ITS AXIS OFF THE EAST COAST...WHILE A LOW PRES SYSTEM
LIFTS NE INTO THE GREAT LAKES. THE RESULT WILL BE A BIT OF
STRENGTHENING OF SWLY RETURN FLOW ATOP THE CWFA. GUIDANCE STILL
HINTS AT SOME LOW STRATUS DEVELOPMENT AROUND DAYBREAK...MAINLY FROM
THE I-85 CORRIDOR AND SOUTH...AS SOME ATLANTIC MOISTURE WRAPS AROUND
THE SYSTEM. ANY STRATUS THAT DOES DEVELOP SHUD SCATTER OUT BY
MIDDAY...LEAVING A BKN-OVC CIRRUS DECK. THICKNESSES CONTINUE TO
INCREASE WITH THE AMPLIFYING RIDGE. SO DESPITE PERHAPS MORE CLOUD
COVER...TEMPS SHUD BE AS WARM...IF NOT A CATEGORY OR SO WARMER THAN
TODAY/S READINGS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
AS OF 130 PM EST THURSDAY...MODELS CONTINUE TO AGREE THAT 592 DM
ANTICYCLONE WILL BUILD OFF THE SE COAST WHILE A SOUTHERN STREAM CUT
OFF LOW WILL SWING ACROSS THE DESERT SW. THE CUT OFF LOW IS EXPECTED
TO OPEN UP AS IT LIFTS NE ACROSS THE MISSISSIPPI VALLEY THROUGH SAT
NIGHT ALLOWING DEEP SWLY FLOW ALOFT TO PERSIST ACROSS THE FORECAST
AREA THRU THE PERIOD.

AT THE SURFACE...HIGH PRESSURE CENTERED ACROSS THE WESTERN ATLANTIC
WILL CONTINUE TO RIDGE INTO THE FORECAST AREA FRI NIGHT INTO
SATURDAY BRINGING PERSISTENT MOIST SOUTHERLY FLOW TO THE AREA.
MEANWHILE...A FRONTAL BOUNDARY EXTENDING FROM THE OHIO VALLEY TO THE
SOUTHERN GULF STATES WILL SLOWLY PROGRESS EASTWARD WITH A SURFACE
LOW DEVELOPING ACROSS THE WESTERN GULF COAST RIDING UP ALONG THE
FRONTAL BOUNDARY INTO THE OHIO VALLEY BY 12Z ON SUNDAY. WITH
INCREASING MOISTURE/WARM AIR ADVECTION S/SW FLOW AHEAD OF THE
APPROACHING FRONT...SKY WILL REMAIN MOSTLY CLOUDY ACROSS MUCH OF THE
REGION WITH UPSLOPE INDUCED PRECIP DEVELOPING ACROSS THE SW MTNS BY
SAT AFTERNOON. PRECIP WILL OVERSPREAD THE REGION THROUGH SAT NIGHT
AS A STRONG LOW LEVEL H85 JET OF 50-60KTS MOVES ACROSS THE REGION
AHEAD OF THE FRONT RESULTING IN DEEPER MOISTURE AND BETTER WARM AIR
ADVECTION LIFT. HOWEVER...WITH THE LACK OF THE UPPER FORCING AND A
PRESENCE OF THE MID-LEVEL INVERSION WHICH WILL OFFSET THE OVERALL
LIFTING...PRECIP SHOULD REMAIN RELATIVELY LIGHT UNTIL THE FRONT
REACHES THE AREA. THEREFORE...HAVE MENTIONED LOW END CHANCE POPS
ACROSS MOST LOCATIONS WITH HIGHER CHANCE ACROSS THE WESTERN MTNS.
THANKS TO INCREASING THICKNESS AND WARM AIR ADVECTION...TEMPERATURES
STAY AROUND 10-15 DEGREES ABOVE NORMAL THRU THE PERIOD.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 200 PM EST THURSDAY...MAIN FEATURE TO DEAL WITH IN THE
EXTENDED RANGE OF THE FORECAST IS THE MUCH ADVERTISED COLD FRONTAL
PASSAGE IN THE SUNDAY INTO MONDAY TIMEFRAME. THE 12Z SUITE OF
OPERATIONAL MODELS HAVE TRENDED FASTER WITH THE APPROACHING COLD
FRONT WITH THE GFS/NAM AND CMC PUSHING THE FRONTAL ZONE ACROSS MOST
OF THE AREA ON SUNDAY...WHICH MATCHES UP QUITE WELL WITH THE 09Z
SREF. THE 00Z ECM WAS ALMOST 12 HOURS SLOWER...BUT A QUICK LOOK AT
THE 12Z RUN SHOWS A FASTER SOLUTION. THE OTHER COMPONENT TO THIS IS
THAT WITH THE SW FLOW REMAINING ALOFT...THE FRONT WILL SLOW AND A
FRONTAL WAVE IS LIKELY TO DEVELOP AS A TROUGH ROTATES THROUGH THE
GREAT LAKES. THE FRONT MAY BECOME QUASI-STATIONARY BY EARLY MON JUST
SOUTH AND EAST OF THE FORECAST AREA AS THE WAVE DEVELOPS. THE CMC
HAS BEEN DEEPER WITH THE GREAT LAKES TROUGH AND REMAINS AN OUTLIER.
WILL INSTEAD STAY CLOSER TO THE WPC IDEA OF DEVELOPING A WEAKER
FRONTAL WAVE EARLY ON MON...WHICH AS IT MOVES NE ALLOWS THE
CLOUDS/PRECIP ASSOCIATED WITH THE FRONTAL ZONE TO EXIT ALL OF THE
AREA BY LATE MONDAY. THIS IS ESSENTIALLY A GFS/ECM BLEND. THE UPSHOT
IS THAT CATEGORICAL RAIN/POPS WILL TRAVERSE THE AREA SUN INTO SUN
NIGHT...AND WILL NEED HANG ONTO RATHER ROBUST POPS ACROSS EASTERN
AREAS EARLY MONDAY...BEFORE TRENDING THEM QUICKLY DOWNWARD MON
AFTERNOON.

IN REGARD TO IMPACTS...THE UNSEASONABLY WARM TEMPS WILL CONTINUE ON
SUN...BUT CLOUDS WILL LIKELY LIMIT THE CHANCE FOR ANY RECORD HIGH
TEMPS TO BE ACHIEVED...THOUGH CHARLOTTE WILL MAKE A RUN AT THEIR
RECORD HIGH OF 72 FOR 22 DEC. RAINFALL WILL BE MODERATE TO PERHAPS
EVEN HEAVY AT TIMES WITH THE FRONT. STORM TOTAL PRECIP MAY BE AROUND
3 INCHES IN SOME OF THE USUAL UPSLOPE ENHANCED AREAS OVER WESTERN NC
AND THE UPSTATE...WITH 1-2 INCHES A GOOD BET ELSEWHERE.
HOWEVER...THESE VALUES SHOULD NOT BE SUFFICIENT TO PRODUCE ANY
SIGNIFICANT FLOODING ISSUES. IT ALSO LOOKS LIKE THE SEVERE STORM
POTENTIAL WILL BE MINIMAL AS AS CLOUDS LIMIT THE AMOUNT OF CAPE TO
JUST A COUPLE HUNDRED JOULES AT BEST. WIND FIELDS WILL BE
ROBUST...BUT SOUNDING DATA INDICATES THAT ADVISORY LEVEL SPEEDS WILL
PROBABLY BE LIMITED TO ELEVATIONS ABOVE 3500 FT.

THE PASSAGE OF THE COLD FRONT WILL PUT AN END TO THE MILD TEMPS BY
TUESDAY AS CANADIAN HIGH PRESSURE BUILDS OVER THE REGION FROM THE
NW. TEMPS WILL BE SOMEWHAT BELOW AVERAGE TUE AND WED WITH MODERATION
TOWARD NORMAL VALUES BY THU. LOOKS LIKE DRY WEATHER SHOULD HOLD TUE
THROUGH THU AS THE HIGH SLOWLY MOVES TO THE EAST OF THE AREA BY
THU.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AT KCLT...VFR. SFC HIGH PRESSURE WILL REMAIN CENTERED OVER THE
WESTERN ATLANTIC AS A COLD FRONT SLOWLY SLIDES EAST ACROSS THE
CENTRAL CONUS THROUGH THE TAF PERIOD. WITHIN THE MID LEVELS...FLAT
SW-NE HEIGHTS WILL REMAIN ACROSS THE WESTERN CAROLINAS. THE MID
LEVEL FLOW SHOULD CONTINUE TO STREAM PATCHES OF THICK CIRRUS ACROSS
THE REGION...ESPECIALLY TONIGHT. RETURN FLOW COULD DEVELOP A PLUME
OF LLVL MOISTURE ACROSS THE COASTAL PLAIN TONIGHT. HOWEVER...LATEST
GUIDANCE KEEPS THE BEST MOISTURE ALONG AND EAST OF I-20 TONIGHT. I
WILL INDICATE LIGHT SSW WINDS AND SCT TO BKN CIRRUS
OVERNIGHT...TEMPO SCT015 AROUND SUNRISE. DAYTIME MIXING SHOULD
SUPPORT MARGINAL GUSTS BY MID DAY...REMAINING THROUGH THE AFTERNOON.

ELSEWHERE...VFR. TERMINALS WILL REMAIN WEST OF THE ANTICIPATED PLUME
OF LLVL MOISTURE. TAFS WILL FEATURE SCT TO BKN CIRRUS WITH LIGHT SW
WINDS TONIGHT...INCREASING TO 6-9 KTS DURING THE DAYLIGHT HOURS FRI.

OUTLOOK...MOISTURE CONTINUES TO INCREASE THRU THE WEEKEND...WITH
RESTRICTIONS LIKELY EACH MORNING. RAIN CHANCES INCREASE GRADUALLY
FROM FRI THRU SUN BEFORE A COLD FRONT PASSES THRU SUN NIGHT INTO
MONDAY. PERIODIC RESTRICTIONS LIKELY IN RAIN. CONDITIONS IMPROVE
MONDAY.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-23Z
KCLT       HIGH 100%     HIGH 100%     MED   75%     HIGH 100%
KGSP       HIGH 100%     HIGH  94%     MED   71%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH  85%     HIGH 100%
KGMU       HIGH 100%     HIGH  88%     MED   71%     HIGH 100%
KAND       HIGH 100%     HIGH  97%     MED   70%     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

&&

.FIRE WEATHER...
A DRY CONTINENTAL AIRMASS HAS RESULTED IN RH VALUES DROPPING INTO
THE 15 TO 25 PERCENT RANGE THIS AFTERNOON. FORTUNATELY...WINDS HAVE
REMAINED WELL BELOW RED FLAG CRITERIA. HOWEVER...SOME OCCASIONAL
LOW-END GUSTS IN THE 15 TO 20 MPH RANGE. RH WILL RECOVER THIS
EVENING...AND IS NOT EXPECTED TO BE NEARLY AS LOW ON FRIDAY.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JOH
NEAR TERM...NED
SHORT TERM...JOH
LONG TERM...LG
AVIATION...NED
FIRE WEATHER...