Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 231806
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
106 PM 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 1230 AM...KGSP RADAR SHOWS AN AREA OF LIGHT TO MODERATE
RAIN...WITH EMBEDDED HEAVY RAIN AND THUNDER...OVER THE LAKELANDS AND
MUCH OF THE REST OF UPSTATE SC. THIS AREA OF PRECIP WILL CONTINUE TO
MOVE N AND E ACROSS THE AREA MAINLY E OF THE BLUE RIDGE THRU MID
AFTERNOON. EXPECT ADDITIONAL LIGHTNING STRIKES ACROSS THE AREA S/E
OF I-85 WHERE THE MODELS INDICATE SOME POTENTIAL FOR ELEVATED CAPE.
STILL THINK THERE ARE PATCHES OF LIGHT RAIN AND DRIZZLE THAT THE
RADAR CANNOT SEE...PARTICULARLY OVER THE MTNS...SO THE RELATIVELY
HIGH POP WILL REMAIN ACROSS THE WHOLE FCST AREA. COOL TEMPS ARE
HOLDING IN THE WEDGE.

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...FLYING CONDITIONS APPEAR RATHER GRIM OVER THE NEXT 24
HOURS...WITH WIDESPREAD IFR/LOW IFR CONDITIONS EXPECTED TO CONTINUE
AT LEAST THROUGH THE OVERNIGHT HOURS. AM MONITORING TSRA OVER
UPSTATE SC AND WILL AMEND TAF IF LTG APPROACHES FROM THE S/SW. WILL
NOT RULE OUT SOME BRIEF MVFR PERIODS...ESPECIALLY AFTER ANY SHOWER
ACTIVITY...BUT CONFIDENCE IS FAIRLY HIGH THAT IFR WILL BE AS GOOD AS
IT GETS FOR LONG STRETCHES OF TIME. THE GUIDANCE ACTUALLY GOES WITH
VERY LOW IFR TONIGHT AS ISENTROPIC LIFT CONTINUES OVER THE TOP OF
THE PERSISTENT OLD WEDGE ACROSS THE PIEDMONT. HAVE OPTED TO TRY TO
STAY MORE OPTIMISTIC WITH MERELY LOW IFR FOR NOW...BUT EXPECT AT
LEAST A TEMPO GROUP WITH LATER ISSUANCES TO ACCOUNT FOR PERIODS OF
VLIFR. THROUGH THE EVENING AND MUCH OF THE OVERNIGHT...THERE SHOULD
BE AN EASTERLY CROSSWIND. AS THE LOW LEVEL JET ARRIVES AFTER
MIDNIGHT...EXPECT A PERIOD WITH SOME LOW LEVEL WIND SHEAR FROM THE
SOUTH...WHICH RAMPS UP AROUND 06Z. HARD TO SAY WHEN A WIND SHIFT
WILL START TO OCCUR TO SE AFTER SUNRISE AS WEDGES ARE SOMETIMES
STUBBORN. COMPROMISED ON 13Z IN ORDER TO BEGIN A PROB30 FOR
TSRA...WHEN IN FACT THE WIND SHIFT MIGHT NOT BE UNTIL CLOSER TO THE
END OF THE PERIOD. THE TIMING WILL BE FINE TUNED LATER.

ELSEWHERE...VERY SIMILAR TO KCLT OUTSIDE THE MTNS WITH WIDESPREAD
IFR/LIFR CONDITIONS AND A NE WIND UNDER THE WEDGE. THE ONLY
DIFFERENCE WILL BE TIMING THE DESTRUCTION OF THE WEDGE WITH A
SOUTHERLY WIND SHIFT...WHICH SHOULD BEGIN BY 14Z OR SO AT KAND BUT
IS NOT LIKELY TO REACH THE REST OF THE NON-MTN TAFS BEFORE THE END
OF THE PERIOD. AT KAVL...WIND WILL BE MORE SE THROUGH 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...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       MED   75%     HIGH  83%     HIGH  94%     HIGH  88%
KGSP       HIGH  80%     HIGH  80%     HIGH  94%     HIGH  95%
KAVL       HIGH  86%     HIGH  84%     HIGH  90%     HIGH 100%
KHKY       MED   72%     HIGH  84%     HIGH  87%     HIGH  90%
KGMU       MED   73%     HIGH  80%     HIGH  94%     HIGH  95%
KAND       MED   75%     HIGH  87%     HIGH  95%     HIGH  80%

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...PM


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