000
FXUS62 KGSP 090239
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
939 PM EST SUN DEC 8 2013

.SYNOPSIS...
EXPECT THE INFLUENCE OF CANADIAN HIGH PRESSURE CENTERED OVER NEW
ENGLAND TO BREAK DOWN FOR THE CAROLINAS AS IT MOVES EAST AND
OFFSHORE. ANOTHER COLD FRONT IS EXPECTED TO CROSS THE AREA EARLY
TUESDAY WITH RELATIVELY COLD HIGH PRESSURE BUILDING BACK IN ON
WEDNESDAY AND REMAINING OVER THE REGION THROUGH FRIDAY.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 935 PM...HAVE ALLOWED THE WINTER WEATHER PRODUCTS TO EXPIRE AS
SCHEDULED. TEMPS/WET BULBS CONTINUE TO SLOWLY WARM OR REMAIN STEADY
NEAR AND/OR JUST ABOVE FREEZING. ANY LOCATIONS THAT ARE BELOW
FREEZING ARE VERY ISOLATED AND WHERE PRECIP IS VERY LIGHT.
THEREFORE...ANY ICING WILL BE LIGHT AND ISOLATED AND LIMITED TO
ELEVATED SURFACES. HAVE ISSUED AN SPS TO COVER THESE AREAS AND THIS
SCENARIO. BEST PRECIP AMOUNTS OVERNIGHT WILL REMAIN OVER THE SWRN
MTNS AND TN BORDER AREAS WITH VERY LIGHT RAIN/DRIZZLE ELSEWHERE.
STILL EXPECT AREAS OF FOG TO DEVELOP OVERNIGHT WITH SOME PATCHY
DENSE FOG UNTIL MID MORNING WHEN IT MAY BECOME MORE WIDESPREAD.
UPDATED TEMP TRENDS WITH THE LATEST GUIDANCE AS WELL.

AS OF 655 PM...RADAR CONTINUES TO SHOW AREAS OF MODERATE RAIN MOVING
ACROSS THE MTNS WITH MORE ON THE WAY. ONLY PATCHY LIGHT RAIN AND
DRIZZLE FALLING ELSEWHERE. TEMPS AND WET BULBS FELL A LITTLE THIS
AFTERNOON OVER THE NC ESCARPMENT AND I-40 CORRIDOR. HOWEVER...THEY
ARE NOW ON THE RISE AS RAIN MOVES IN WITH WARMING AND LATENT HEAT
RELEASE. THE SLOW WARMING SHUD CONTINUE THIS EVENING WITH THE THREAT
OF SIGNIFICANT FREEZING PRECIP ENDING AT 8 PM IN LINE WITH THE
WINTER WEATHER PRODUCTS. IN ANY CASE...THE PRECIP OVER THE COLDEST
AIR WILL BE VERY LIGHT...SO NO SIGNIFICANT ICING IS EXPECTED BEFORE
WARMING. GUIDANCE NOW SHOWING DENSE FOG POTENTIAL OUTSIDE OF THE
MTNS AS THE CAD SLOWLY ERODES FROM THE TOP DOWN MON MORNING. WHILE
THE TIMING MAY NOT BE EXACT...THIS IS THE USUAL WX TREND WHEN THIS
OCCURS. THEREFORE...HAVE INCLUDED THIS IN THE FORECAST AS WELL. ALL
FIELDS HAVE BEEN UPDATED TO SHOW THESE TRENDS.

AS OF 345 PM...RADAR SHOWING AREA OF MODERATE RAIN MOVING INTO THE
MTNS FROM THE SW WITH ONLY SPOTTY RAIN/DRIZZLE ELSEWHERE. EXPECT
THIS PRECIP TO SPREAD NE ACROSS THE WRN CWFA THEN SPREAD EAST THRU
THE EVENING. LATEST OBS SHOW SFC WET BULBS STILL BELOW FREEZING
ALONG THE ESCARPMENT OF THE NRN FOOTHILLS THEN EAST NORTH OF I-40.
THESE AREAS MAY STILL SEE SOME FZRA AS THIS PRECIP MOVES IN BEFORE
WARMING ABOVE FREEZING THIS EVENING. THEREFORE...NO CHANGES TO
CURRENT WWA PRODUCTS. THAT SAID...EVEN WITH THE MODERATE RAIN
MOVING IN...ANY DAMAGING ICE ACCUMS WOULD BE ISOLATED. MADE
ADJUSTMENTS TO ALL FIELDS BASED ON CURRENT CONDITIONS AND LATEST MDL
GUIDANCE.

AT 230 PM EST SUNDAY...A STRONG SHORTWAVE WILL MOVE INTO AN UPPER
TROUGH PROGRESSING FORM THE ROCKIES TO THE PAINS TONIGHT AND
MONDAY...WHILE AN UPPER RIDGE AXIS MOVES OFF THE EAST COAST. A
SURFACE RIDGE ALONG THE EASTERN SEABOARD WILL SLOWLY WEAKEN...WHILE
A COLD FRONT MOVES EAST ACROSS THE GULF STATES.

SURFACE TEMPERATURES HAVE CONTINUED TO COOL SLIGHTLY ALONG TH
NORTHERN NC BLUE RIDGE AS EVAPORATIVE COOLING TAKES TEMPERATURES
DOWN TOWARD WET BULBS. MODEL DATA INDICATED THAT THIS TRENT WILL
CONTINUE...AND FREEZING PRECIPITATION MAY CONTINUE INTO THE EARLY
EVENING ALONG THE NORTHERN BLUE RIDGE...ALBEIT LIGHTLY.

ISENTROPIC UPGLIDE OVER THE SURFACE RIDGE WILL WEAKEN TONIGHT AS LOW
LEVEL FLOW VEERS FROM SW TO SE...HOWEVER THIS SAME VEERING FLOW WILL
TAP GULF MOISTURE AHEAD OF THE FRONT...FEEDING IT INTO THE SOUTHERN
APPALACHIANS. UPSLOPE FLOW WITH THESE VEERING WINDS WILL BE SOMEWHAT
LIMITED AS THE COMPONENT ORTHOGONAL TO THE BLUE RIDGE DECREASES...
THIS FLOW WILL STILL CLIMB ELEVATED TERRAIN...AND THE SOUTHEAST
MOUNTAINS IS WHERE THE GREATEST ACCUMULATIONS WILL FALL. SOME
INSTABILITY WILL BE PRESENT IN NC ALONG THE TN BORDER...WHERE A
SMALL CHANCE OF THUNDERSTORMS WILL BE CARRIED.

MINIMUM TEMPERATURES TONIGHT WILL RUN AROUND NORMAL EAST OF THE
MOUNTAINS..IN INITIALLY COOL NE FLOW...AND ABOVE NORMAL IN THE
MOUNTAINS. HIGH TEMPERATURES MONDAY WILL BE SLIGHTLY BELOW NORMAL
UNDER PERSISTENT CLOUD COVER.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 215 PM SUNDAY...STALLED FRONTAL ZONE WILL EXTEND ACRS THE
SOUTHEAST TUESDAY NIGHT ON FRINGE OF BERMUDA HIGH. SHORTWAVE ROUNDS
BASE OF LONGWAVE UPPER TROUGH ACRS THE CENTRAL U.S. AND SPRAWLING
HIGH PRESSURE BUILDS EASTWARD IN ITS WAKE. SW FLOW ALOFT WILL SUPPLY
GULF MOISTURE ALONG THE FRONT. TUE EVENING THERMAL ADVECTION LOOKS
QUITE WEAK IN LLVLS AND FORCING IS THEREFORE LIMITED. MIDLEVELS
REMAIN WARM HOWEVER ALLOWING FOR MINOR ELEVATED INSTABILITY. THIS
MAY INDEED BE THE PRIMARY DRIVER FOR PRECIP AT THIS TIME. LLVL SHEAR
IS STRONG BUT CONTAINED BELOW THE CONVECTIVE LAYER...SO SEVERE WX
NOT A THREAT...ESPECIALLY GIVEN LOW MUCAPE.

MEANWHILE...COLD ADVECTION SHOULD ALREADY BE UNDERWAY MON NIGHT ON
THE WEST SIDE OF THE APPALACHIANS...AND NW UPSLOPE FLOW STARTS TO
BECOME A FACTOR IN THE MTNS. CONCURRENT DEVELOPMENT OF A WEAK
FRONTAL WAVE SUGGESTED BY BOTH NAM/GFS TOWARD DAYBREAK TUE WILL
ALLOW FOR SLIGHT UPTICK IN WARM ADVECTION OVER THE PIEDMONT. POPS
THUS INCREASE ACRS THE FORECAST AREA BY 12Z TUE ALBEIT FOR DIFFERENT
REASONS. PLENTIFUL MOISTURE AND FIXED POSITION OF FRONT APPEAR TO
KEEP SUBFREEZING TEMPS AT BAY MON NITE AND TUE MRNG. THUS ALL LIQUID
PRECIP EXPECTED AT THAT TIME...WITH EVEN HIGH ELEVATIONS DROPPING
ONLY TO THE MID 30S. I SUPPOSE IN UPSLOPE AREAS THAT A FEW FLURRIES
COULD MIX WITH RAIN AT THOSE TEMPS. COLD ADVECTION STARTS TO MAKE
INROADS INTO THE CWFA DURING THE DAY TUE WITH DRIER AIR PUSHING IN
AND DIMINISHING POPS NW TO SE THRU THE DAY. UPSLOPE CONTINUES
HOWEVER SO NEAR THE TENN BORDER SOME LIGHT PRECIP MIGHT CONTINUE
INTO TUE EVENING. HIGH ELEVATIONS POSSIBLY WILL SEE A PTYPE
CHANGEOVER DURING THE DAY WITH COOLING TEMPS. DRYING UPPER LEVELS
SUGGEST FZRA WOULD RESULT...BUT UPSLOPING MIGHT PRODUCE SOME RIME
ICE INSTEAD. POPS ARE LOW BY ONSET OF ANY FZRA AND ACCUMS ARE
MINIMAL.

POPS SHOULD END EARLY ENOUGH TUE EVENING THAT NO PTYPE CONCERNS
EXIST OVER THE LOWER ELEVATIONS OR PIEDMONT. TEMPS WILL DROP A FEW
DEGREES BELOW NORMAL ACRS THE AREA WED MRNG. DRY HIGH PRESSURE
BUILDS IN FOR WEDNESDAY AND HIGH TEMPS REMAIN BELOW NORMAL.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 225 PM EST SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
THURSDAY WITH A RELATIVELY FLAT UPPER PATTERN OVER THE REGION AND
BROAD UPPER TROFFING WELL TO OUR NORTH. THE CENTER OF THE SURFACE
HIGH PRESSURE CROSSING THE SE STATES WILL BE OVER OUR AREA EARLY
FRIDAY. THIS HIGH WILL BE MOVING OFF THE CAROLINA COAST LATE FRIDAY
AS THE NEXT SYSTEM APPROACHES FROM THE WEST. A SHORTWAVE CROSSING
TEXAS ON FRIDAY WITH GOOD SOUTHERLY FLOW AHEAD OF THE SYSTEM
SATURDAY. THE GFS HAS A DEEPER A SLOWER MOVING TROUGH WHICH IS
BRIEFLY CLOSED AT 18Z SATURDAY OVER NEW MEXICO.  AT 12Z SUNDAY THE
GFS HAS IT OVER EASTERN OKLAHOMA AS AN OPEN BUT STILL SIGNIFICANT
TROUGH WITH DEEP CONVECTION ACROSS THE GULF STATES. AT 12Z
SUNDAY...THE ECMWF HAS A MUCH FLATTER TROUGH OVER WESTERN TN AND HAS
CARRIED THE HEAVIER PRECIP FROM NORTH FLORIDA TO OFF THE SC COAST
WHILE OUR AREA HAS SOME BROAD MOSTLY LIGHT PRECIP. THERE IS A BIG
DIFFERENCE IN THE 06Z GFS AND 12Z GFS IN THAT 06Z HAD THE CAROLINAS
DRY ON SUNDAY AND NOW WIDESPREAD RAIN ON SUNDAY WITH THE NEWEST 12Z
RUN. THIS CAUSED ISSUES WITH FORECAST COORDINATION WHICH IS NOW
RESOLVED. NEWEST GFS KEEPS PRECIP OVER EASTERN SECTIONS EVEN AT 12Z
MONDAY...BUT GOING WITH THE DRYING TREND SUNDAY NIGHT. ECMWF HAS
EVERYBODY DRY AT 12Z MONDAY.

BUFKIT HAS AVL WITH ALL RAIN THROUGH THE WHOLE SYSTEM.

TEMPERATURES A FEW DEGREES BELOW NORMAL THROUGH THE PERIOD.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
AT KCLT...VERY PESSIMISTIC SET OF TAFS THIS PERIOD AS COPIOUS LOW
LEVEL MOISTURE AND UPGLIDE REMAIN OVER THE AREA THRU MON MORN. THIS
WILL LEAD TO IFR CONDITIONS FALLING TO LIFR OVERNIGHT. AS THE WEDGE
ACROSS THE AREA ERODES FROM THE TOP DOWN...EXPECT VLIFR FOG AND CIGS
TO DEVELOP BY MID MORNING. CONDITIONS SHUD IMPROVE TO IFR FOR THE
AFTERNOON AS THE FLOW BECOMES SWLY BUT THE LOW LEVEL MOISTURE HANGS
IN. RAIN AND DRIZZLE WILL CONTINUE THRU THE PERIOD BUT WILL BE ALL
LIQUID AS SFC TEMPS REMAIN ABOVE FREEZING. ENE WINDS THIS EVENING GO
LIGHT OR CALM OVERNIGHT WITH SWLY WINDS DEVELOPING AFTER DAYBREAK.

ELSEWHERE...SIMILAR CONDITIONS TO KCLT. KAND WILL TAKE LONGER TO
FALL THIS EVENING. KAVL WILL SEE LLWS TOWARD DAYBREAK AS THE LOW
LEVEL FLOW TURNS SWLY BUT THE SFC FLOW IS SELY. SFC WINDS WILL THEN
MATCH LOW LEVEL FLOW FROM LATE MORNING ON. CANNOT COMPLETELY RULE
OUT A BRIEF PERIOD OF FREEZING RAIN/DRIZZLE AT KHKY FOR UNTIL 02Z OR
SO. HOWEVER...THE CHC IS MINIMAL. ELSEWHERE...INCLUDING KAVL...ONLY
LIQUID RAIN IS EXPECTED.

OUTLOOK...RESTRICTIVE CIGS AND VSBY CAN BE EXPECTED IN PRECIPITATION
MON NITE AND TUE MORN. DRIER AIR AND BETTER FLIGHT CONDITIONS MAY
RETURN TUE AFTERNOON BUT COULD HOLD OFF UNTIL WEDNESDAY.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       MED   70%     MED   72%     MED   73%     HIGH  88%
KGSP       MED   70%     MED   76%     MED   76%     HIGH  91%
KAVL       HIGH  87%     MED   75%     MED   67%     MED   79%
KHKY       MED   74%     MED   77%     MED   73%     MED   75%
KGMU       MED   70%     MED   72%     MED   72%     HIGH  91%
KAND       MED   71%     MED   76%     MED   76%     HIGH  82%

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...JAT/RWH
SHORT TERM...WIMBERLEY
LONG TERM...DEO
AVIATION...RWH