Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 220753
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
253 AM EST MON DEC 22 2014

.SYNOPSIS...
A MOIST AIR MASS WILL REMAIN ACROSS THE REGION BEFORE A COLD FRONT
CROSSES THE AREA ON WEDNESDAY. DRY HIGH PRESSURE ARRIVE FOR THURSDAY
AND FRIDAY. ANOTHER COLD FRONT WILL CROSS THE AREA ON SATURDAY...
FOLLOWED BY HIGH PRESSURE ON SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 200 AM EST...ON THE LATEST SFC ANALYSIS...HIGH PRESSURE RIDGES
SWD ACROSS THE WRN CAROLINAS FROM A 1028 MB HIGH PRES CENTER OVER
ERN PA EARLY THIS MORNING. A NARROW UPPER JETLET STRETCHING FROM THE
MS GULF COAST THROUGH THE SRN APPALACHIANS TO THE DELMARVA PENINSULA
IS AIDING WEAK MOIST UPGLIDE OVER THIS CAD LAYER...AND LIGHT RAIN
AND DRIZZLE WILL RESULT OVER MUCH OF THE FORECAST AREA THROUGH LATE
MORNING UNTIL THE UPPER JET SLIDES SE AND WEAKENS. ANY LINGERING
SPOTTY FREEZING DRIZZLE ALONG THE NRN BLUE RIDGE THROUGH DAYBREAK
SHOULD BE VERY ISOLD AND BRIEF. OTHERWISE...THE CAD WILL REMAIN IN
PLACE THROUGH THE DAY DESPITE THE GRADUALLY WEAKENING ISENTROPIC
LIFT. THIS SHOULD HOLD TEMPERATURES IN THE UPPER 30S TO MIDDLE 40S
THROUGHOUT THE REGION TODAY...EXCEPT FOR SOME LOWER 50S IN THE SW
MTNS OUTSIDE THE CAD REGIME.

MEANWHILE...A DEEP TROUGH STRETCHING FROM THE NRN PLAINS TO E TX
WILL SEE HEIGHTS CLOSING OFF OVER THE CENTRAL CONUS THROUGH TONIGHT.
THE MAIN DOWNSTREAM RESULT OF THIS WILL BE RESURGENT UPGLIDE TONIGHT
ALONG WITH SLIGHTLY DEEPER MOISTURE. WILL ALLOW POPS TO REBOUND TO
HIGH CHC TO LIKELY FOR MAINLY LIGHT RAIN...AND TEMPERATURES WILL
GENERALLY REMAIN STEADY THROUGH THE NIGHT.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AT 230 AM EST MONDAY...ON TUESDAY MORNING A CLOSED UPPER LOW WILL BE
MOVING FROM THE CENTRAL PLAINS TO THE MID MS RIVER VALLEY...WITH A
TROUGH EXTENDING SOUTH INTO NE MEXICO...AND RIDGING DOWNSTREAM OFF
THE EAST COAST. THE UPPER LOW MOVES NE ACROSS THE GREAT LAKES BY
WEDNESDAY...WHILE THE TROUGH AXIS MOVES VERY LITTLE. THE TROUGH THE
RAPIDLY PROGRESSES ACROSS THE MS RIVER VALLEY TO THE APPALACHIANS
LATE WEDNESDAY NIGHT.

A COLD AIR DAMMING SCENARIO WILL EXIST OVER THE WESTERN CAROLINAS
AND N GA ON TUESDAY...WHILE A COLD FRONT SLOWLY CROSSES THE TN VALLEY
AND GULF STATES. ISENTROPIC UPGLIDE OVER AN EAST COAST SURFACE HIGH
WILL SUPPORT WIDESPREAD AND PROLONGED PRECIPITATION.

A SURFACE WAVE DEVELOPS MOVES NORTH ALONG THE FRONT IN THE GULF
STATES AND TN TUESDAY NIGHT...WHILE THE CAD WEDGE WEAKENS. ROBUST
MOIST SOUTHERLY LOW LEVEL FLOW SETS UP INTO THE SOUTHERN
APPALACHIANS. AT THIS POINT THERE REMAINS SOME UNCERTAINTY AS TO HOW
MUCH INSTABILITY AND SHEAR WILL BE PRESENT OVER OUR AREA AHEAD OF
THE COLD FRONT AND WEDNESDAY...BUT THE BEST SUPPORT FOR SEVERE
WEATHER APPEARS TO BE TO OUR SOUTH. THE FRONT MOVES THROUGH ON
WEDNESDAY...FOLLOWED BY COLD ADVECTION AND NW FLOW SNOW SHOWERS OVER
THE NC MOUNTAINS.

TEMPERATURES WILL EXHIBIT A VERY LOW DIURNAL RANGE ON TUESDAY AND
TUESDAY NIGHT...AS CLOUD COVER AND MOISTURE HOLD MAXIMUMS BELOW
NORMAL AND MINIMUMS ABOVE NORMAL. WARMING IMMEDIATELY AHEAD OF THE
FRONT WILL BRING HIGH TEMPERATURES ABOVE NORMAL ON WEDNESDAY. COLD
ADVECTION BEHIND THE FRONT WILL BE PARTIALLY OFFSET BY DOWNSLOPE
WARMING EAST OF THE MOUNTAINS...AND MINIMUM TEMPERATURES WILL BE
SLIGHTLY ABOVE NORMAL.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AT 230 AM EST MONDAY...ON THURSDAY MORNING UPPER TROUGHS WILL BE
OVER THE EAST AND THE WEST...WITH A LOW AMPLITUDE UPPER RIDGE OVER
THE PLAINS. BY FRIDAY MORNING THE RIDGE AXIS WILL HAVE PROGRESSED TO
THE EAST COAST...WHILE THE TROUGH UPSTREAM WILL HAVE REACHED THE
EAST SLOPES OF THE ROCKIES. THE TROUGH WILL CROSS THE PLAINS ON
SATURDAY. BY SUNDAY THE ECMWF AND GFS ARE OUT OF PHASE...WITH THE
FORMER PLACING ITS HIGHLY AMPLIFIED TROUGH OVER THE MS RIVER VALLEY
AND THE LATER HAVING ITS DEAMPLIFIED TROUGH OVER THE EAST
COAST...WITH A LOW AMPLITUDE RIDGE OVER THE MS RIVER VALLEY...AND
ANOTHER LOW AMPLITUDE TROUGH OVER THE PLAINS...WITH NEARLY ZONAL
FLOW OVER THE SOUTHERN TIER OF STATES.

A COLD FRONT WILL BE DEPARTING THE EAST COAST ON THURSDAY...WITH
DRYING DOWNSLOPE FLOW IN THE LEE OF THE MOUNTAINS...AND SOME
LINGERING UPSLOPE FLOW SNOW SHOWERS IN THE NC MOUNTAINS BORDERING
TN. THE UPSLOPE/DOWNSLOPE REGIME ENDS LATE THURSDAY AS HIGH PRESSURE
CROSSES THE GULF...AND BY FRIDAY MORNING....GULF INFLOW SETS UP ON
THE BACK SIDE OF THIS HIGH AHEAD OF THE NEXT FRONT. THIS FRONT
CROSSES THE MOUNTAINS LATE FRIDAY NIGHT...BUT GULF INFLOW WEAKENS
BEFORE IT ARRIVES...LIMITING PRECIPITATION. THE FRONT MOVES OFF THE
EAST COAST BY SUNDAY MORNING....WITH ANOTHER ROUND OF NW UPSLOPE
FLOW INTO THE NC MOUNTAINS...SUPPORTING ANOTHER BATCH OF SNOW
SHOWERS. BY MONDAY...DRY HIGH PRESSURE MOVES INTO THE TN VALLEY.

TEMPERATURES WILL WARM FROM NEAR NORMAL THURSDAY TO SLIGHTLY ABOVE
NORMAL FRIDAY IN WARM ADVECTION AHEAD OF THE NEXT FRONT...COOLING TO
SLIGHTLY BELOW NORMAL BEHIND THE FRONT.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
AT KCLT...RADAR SHOWS LIGHT RETURNS MOVING NORTHWARD OVER THE
AIRFIELD THIS MORNING...AND EITHER VERY LIGHT RAIN OR DRIZZLE SHOULD
CONTINUE IN THE UPGLIDE OVER THE SFC CAD LAYER THROUGH MUCH OF THE
DAY. GIVEN LOWERING IFR CIGS OVER THE MIDLANDS OF SC...WILL
ADVERTISE TEMPO IFR THROUGH DAYBREAK AND THEN FAIRLY SOLID IFR
THROUGH MOST OF THE DAY AS DRIZZLE AND LIGHT RAIN GRADUALLY WANE
FROM THE WEST. EXPECT A STEADY NE FLOW AT LESS THAN 10 KT THROUGH
THE PERIOD. DRIZZLE OR LIGHT RAIN WILL RETURN WITH RESURGENT UPGLIDE
BY LATE EVENING.

ELSEWHERE...UPGLIDE MOISTURE OVER THE SFC CAD LAYER WILL YIELD LIGHT
RAIN OR DRIZZLE THROUGHOUT THE REGION THROUGH MOST OF THE MORNING
HOURS...BEFORE TAPERING OFF FROM THE W THIS AFTN. MORE SOLID IFR
CIGS WILL LIKELY DEVELOP FROM S TO N...EXCEPT FOR RATHER QUICK IFR
DEVELOPMENT AT KAVL IN SE FLOW EARLY THIS MORNING. SOME BRIEF
RECOVERY TO LOWER END MVFR IS POSSIBLE THIS AFTN AS THE DRIZZLE
WANES. EXPECT CONTINUED NE FLOW AT LESS THAN 10 KT THROUGH THE
PERIOD AT THE FOOTHILL SITES...EXCEPT SE WINDS AT KAVL. DRIZZLE AND
LIGHT RAIN WILL RETURN THIS EVENING ALONG WITH IFR CIGS.

OUTLOOK...MOISTURE WILL DEEPEN LATE TONIGHT THROUGH TUESDAY NIGHT
AHEAD OF THE NEXT APPROACHING COLD FRONT. LOW RESTRICTIONS AND
WIDESPREAD RAIN SHOWERS ARE EXPECTED. A COLD FRONT WILL CROSS THE
REGION FROM THE WEST ON WED. DRY HIGH PRESSURE WILL RETURN THROUGH
LATE WEEK.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       HIGH  82%     HIGH  80%     HIGH  85%     HIGH  90%
KGSP       HIGH 100%     MED   79%     HIGH 100%     HIGH  87%
KAVL       HIGH  90%     HIGH  87%     HIGH  95%     HIGH  90%
KHKY       HIGH  89%     HIGH  90%     HIGH  92%     HIGH 100%
KGMU       HIGH 100%     MED   79%     HIGH 100%     HIGH  93%
KAND       HIGH  95%     MED   67%     HIGH  97%     HIGH  87%

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...JAT
NEAR TERM...HG
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...HG


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