Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 231625
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1125 AM EST TUE DEC 23 2014

.SYNOPSIS...
A MOIST AIRMASS WILL REMAIN OVER THE REGION BEFORE A COLD FRONT
CROSSES BY TONIGHT. HIGH PRESSURE WILL ARRIVE ON THURSDAY AND LINGER
INTO FRIDAY. ANOTHER COLD FRONT WILL CROSS THE AREA ON SATURDAY AND
SUNDAY...FOLLOWED BY HIGH PRESSURE ON MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1115 AM...BEEN WATCHING AN AREA OF SHOWERS WITH EMBEDDED
THUNDERSTORMS MOVING NWD FROM E CENTRAL GA FOR THE LAST HOUR OR TWO.
WHILE THE WEDGE CONTINUES TO HOLD ACROSS THE SRN ZONES...IT APPEARS
AS THOUGH THERE WILL BE ENUF ELEVATED CAPE ABOVE THE WEDGE TO
MAINTAIN THE STORMS AS THEY MOVE OVER THE LAKELANDS. THE NAM IN
PARTICULAR SHOWS ENUF ELEVATED CAPE TO SUGGEST AN ELEVATED THUNDER
RISK EVERYWHERE ALONG AND S/E OF I-85 THROUGH LATE AFTERNOON...SO A
CHANCE OF THUNDER WILL BE ADDED IN THOSE LOCATIONS. WILL ALSO CHANGE
THE CHARACTER TO CONVECTIVE ACROSS THAT AREA...GIVEN THE INSTABILITY
ALOFT. TEMPS LOOK GOOD. STILL THINK WE HAVE MORE LIGHT RAIN AND
DRIZZLE ELSEWHERE THAT IS NOT SHOWING UP ON THE RADAR.

REMAINDER OF PREVIOUS DISCUSSION...

AS OF 620 AM EST...WATER VAPOR IMAGERY SHOWS A CLOSED CIRCULATION
OVER IOWA THIS MORNING. ENERGY PIVOTING AROUND THE CLOSED SYSTEM
TODAY WILL SHARPEN UP THE MAIN TROUGH AXIS SWD ACROSS THE SRN
PLAINS. MEANWHILE...THE LATEST SFC ANALYSIS SHOWS CONTINUED CAD
ACROSS OUR FORECAST AREA...BUT WITH HIGH PRESSURE WEAKENING SLIGHTLY
TO THE N. AS THE UPPER TROUGH CONSOLIDATES WELL TO THE WEST...
ISENTROPIC LIFT OVER THE CAD MAY BRIEFLY WEAKEN THROUGH LATE MORNING
OR EARLY AFTERNOON. HOWEVER...LOW LEVEL MOISTURE AND STEADY UPGLIDE
WILL STILL BE SUFFICIENT FOR HIGH COVERAGE OF LIGHT RAIN OR DRIZZLE
THROUGH THE PERIOD...ALONG WITH AREAS OF FOG WITHIN THE CAD LAYER AS
THE NE FLOW SLOWLY WEAKENS. EXPECT CHILLY TEMPERATURES TO REMAIN AT
LEAST ONE TO TWO CATEGORIES BELOW THE CONSENSUS OF MOS IN MOST AREAS.

THE MODELS FEATURE EXCELLENT AGREEMENT ON THE SALIENT FEATURES
THROUGH 36 HOURS...WITH THE TROUGH AXIS DEEPENING TONIGHT AS IT
MOVES EWD TOWARD THE MS RIVER VALLEY. AN OPEN GULF AHEAD OF THIS
TROUGH WILL ALLOW MOISTURE TO DEEPEN RAPIDLY TONIGHT...WITH STRONGER
OMEGA RETURNING AS THE 850 MB SRLY JET RAMPS BACK UP. RAINFALL RATES
WILL INCREASE OVERNIGHT AND QPF SHOULD FOCUS MOST STRONGLY IN THE
SRLY UPSLOPE AREAS FROM 06Z TO 12Z. HOWEVER...RAINFALL TOTALS COULD
BE A BIT BELOW MODEL CONSENSUS GIVEN THE EXPECTED GULF COASTAL
CONVECTION. FAIRLY LOW RIVER AND STREAM LEVELS HEADED INTO THE EVENT
SHOULD HELP PRECLUDE HYDRO PROBLEMS WITH ANY HEAVIER RAINFALL LATE
TONIGHT. VERY LIMITED EROSION IN THE SFC WEDGE IS EXPECTED
OVERNIGHT...WITH SLIGHT TEMPERATURE RECOVERY OVER THE FAR SRN/SERN
PIEDMONT SECTIONS LATE. ISOLD ELEVATED CONVECTION SHOULD JUST BECOME
POSSIBLE IN THE EXTREME SRN PIEDMONT TOWARD DAYBREAK WED. ANY WIND
GUSTS REACHING ADVISORY CRITERIA WOULD LIKELY IMPACT ONLY THE VERY
HIGHEST PEAKS OF THE SW MTNS LATE TONIGHT...SO NO NPW HAZARDS ARE
EXPECTED.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AT 230 AM EST TUESDAY...ON WEDNESDAY MORNING A CLOSED UPPER LOW WILL
BE OVER THE MID MS RIVER VALLEY...WITH A HIGH AMPLITUDE TROUGH
EXTENDING SW TO MEXICO...AND HIGH AMPLITUDE RIDGES OFF THE EAST
COAST AND OVER THE WEST. THE UPPER PATTER DEAMPLIFIES BY THURSDAY
MORNING...WITH THE TROUGH PROGRESSING TO THE APPALACHIANS...THE
RIDGE UPSTREAM CROSSING THE PLAINS...AND ANOTHER TROUGH MOVING OVER
THE WEST.

A MODERATE TO STRONG COLD FRONT WILL BE CROSSING THE GULF STATES AND
TN VALLEY WEDNESDAY MORNING. VIGOROUS MOIST SOUTHERLY FLOW AHEAD OF
THIS FRONT WILL BE DIRECTED INTO THE SOUTHERN APPALACHIANS...AND
BOTH ISENTROPIC UPGLIDE AND UPSLOPE FLOW WILL BE PRESENT TO ENHANCE
PRECIPITATION PRODUCTION. THERE IS STILL COME CONCERN THAT GULF
CONVECTION WILL LIMIT THE AMOUNT OF MOISTURE REACHING OUR
AREA...BUT AT THIS TIME IT APPEARS THE 2 TO 3 INCHES OF TOTAL
RAINFALL ARE POSSIBLE...MAXIMIZED NEAR THE ELLICOT ROCK AREA WHERE
NC...SC...AND GA MEET. THE FRONT WILL CROSS OUR AREA DURING THE
AFTERNOON AND EARLY EVENING. INSTABILITY APPEARS TO BE RATHER
LIMITED...AND BEST IN THE EAST...WHILE SHEAR APPEARS TO BE
ROBUST...BUT BEST TO THE WEST. THE SITUATION WILL NEED TO MONITORED
FOR IMPROVEMENT OF SEVERE WEATHER PARAMETERS.

COLD ADVECTION AND MOIST NW FLOW WILL SUPPORT A TRANSITION TO SNOW
SHOWERS IN THE NC MOUNTAINS BORDERING TN ON WEDNESDAY NIGHT. DRY
HIGH PRESSURE MOVING ACROSS THE GULF STATES AND ASSOCIATED WARMING
WILL PUT AND END TO THESE SNOW SHOWERS BY MIDDAY THURSDAY. SNOWFALL
ACCUMULATIONS ARE EXPECTED OT BE MODEST...AND MAINLY AT HIGHER
ELEVATIONS. THE CENTER OF THE DRY HIGH PRESSURE MOVES OVER OUR AREA
ON THURSDAY NIGHT.

TEMPERATURES WILL RUN ABOVE NORMAL ON WEDNESDAY AHEAD OF THE FRONT
IN WARM ADVECTION...AS WELL AS BEHIND THE FRONT WEDNESDAY NIGHT AS
DOWNSLOPE FLOW OFFSETS COLD ADVECTION. TEMPERATURES WILL RUN JUST
ABOVE NORMAL ON THURSDAY AND THURSDAY NIGHT AS HEIGHTS ALOFT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AT 230 AM EST TUESDAY...ON FRIDAY MORNING...AND UPPER RIDGE WILL BE
OVER THE EASTERN USA...WITH A TROUGH OVER THE ROCKIES. THE PATTER
PROGRESSES SLOWLY...SUCH THAT BY SUNDAY THE RIDGE MOVES OFF THE EAST
COAST...AND THE TROUGH STRATUS TO MOVE INTO THE PLAINS. Y MONDAY A
DEVELOPING UPPER LOW DROPS DOWN THE WEST COAST...RESULTING IN
RETROGRESSION OF THE TROUGH AXIS BACK TO THE ROCKIES...AND
AMPLIFICATION OF A WEAK UPPER RIDGE OVER THE OH RIVER VALLEY. THIS
PATTERN PROGRESSES ONLY SLIGHTLY BY TUESDAY.

AT THE SURFACE...HIGH PRESSURE WILL BE CENTERED OVER THE CAROLINAS
ON FRIDAY...WHILE GULF INFLOW MOVES UP THE MS RIVER VALLEY AHEAD OF
A COLD FRONT. THE HIGH MAINTAINS A FOOTHOLD OVER THE CAROLINAS AND GA
ON SATURDAY...WHILE WEAKENING GULF INFLOW SHIFTS EAST INTO THE NT
VALLEY...AS THE FRONT CROSSES THE MS RIVER. THE FRONT CROSSES OUR
AREA EARLY SUNDAY...WITH A SURFACE WAVE MOVING JUST SOUTH OF THE
AREA THAT MAY ENHANCE LIFT AND PRECIPITATION OVER OUR AREA. HIGH
PRESSURE SPREADS EAST ACROSS THE MOUNTAINS BY MONDAY...WITHOUT MUCH
OF A PRESSURE GRADIENT OR ORTHOGONAL FLOW INTO THE MOUNTAINS. THE
OLD BOUNDARY WILL RETURN NORTH AS A WARM FRONT FROM THE SOUTH LATE
MONDAY...SUPPORTING INCREASING CLOUD COVER AND PRECIPITATION CHANCES.

TEMPERATURES WILL RUN SLIGHTLY ABOVE NORMAL AHEAD OF THE FRONT...AND
NEAR NORMAL IN ITS WAKE.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT...LIGHT UPGLIDE OVER THE PERISISTENT CAD REGIME ALONG WITH
LOW LEVEL MOISTURE WILL PERSIST THROUGH THE FIRST HALF OF THE
TERMINAL FORECAST PERIOD...WITH DEEPER MOISTURE AND BETTER FORCING
ARRIVING TONIGHT. SOLID LIFR CIGS AND IFR VSBY WILL RESULT...WITH
LIGHT RAIN OR DRIZZLE AT MOST TIMES THROUGH THE PERIOD. STEADIER
RAIN WILL DEVELOP TONIGHT AS THE SRLY 850 MB JET RAMPS BACK UP FROM
THE WEST. EXPECT SFC WINDS TO REMAIN NE AT LESS THAN 10 KT
THROUGHOUT...BUT POSSIBLY SHIFTING TO ESE WITH THE ARRIVAL OF THE
WEDGE FRONT OVERNIGHT. LLWS LOOKS MORE LIKELY TONIGHT WITH 35 TO 40
KT OF FLOW SHOWING UP AT 2000 FEET LATE.

ELSEWHERE...PERIODS OF LIGHT RAIN AND DRIZZLE WILL CONTINUE IN WEAK
UPGLIDE OVER THE SFC CAD LAYER TODAY. THIS WILL BE ACCOMPANIED BY
LIFR CIGS AND MAINLY MVFR VSBY IN LIGHT FOG WITH SOME MIXING ON
LIGHT NE SFC WINDS...SE AT KAVL. STEADIER RAINFALL WILL DEVELOP
TOWARD EVENING AS THE DEEPER MOISTURE AND UPPER SUPPORT ARRIVE FROM
THE WEST. THE IMPROVING SRLY JET WILL ALSO REQUIRE THE MENTION OF
LLWS AT KAVL DURING THE LATTER HALF OF THE PERIOD.

OUTLOOK...DEEP MOISTURE WILL CONTINUE AT ALL TAF SITES UNTIL A COLD
FRONT CROSSES THE AREA FROM THE WEST LATE WED. WIDESPREAD RAIN
SHOWERS AND ASSOCIATED LOW RESTRICTIONS WILL CONTINUE THROUGH FROPA.
DRY HIGH PRESSURE WILL RETURN THROUGH LATE WEEK.

CONFIDENCE TABLE...

            16-22Z        22-04Z        04-10Z        10-12Z
KCLT       MED   66%     MED   71%     HIGH  88%     HIGH 100%
KGSP       MED   66%     MED   78%     HIGH  85%     HIGH 100%
KAVL       LOW   54%     MED   77%     HIGH  88%     HIGH 100%
KHKY       LOW   37%     MED   71%     MED   72%     HIGH  85%
KGMU       MED   66%     MED   78%     HIGH  85%     HIGH 100%
KAND       MED   66%     MED   71%     HIGH  89%     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...JAT
NEAR TERM...HG/PM
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...HG


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