Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 132047
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
447 PM EDT SUN APR 13 2014

.SYNOPSIS...
WARM SOUTHERLY FLOW WILL PERSIST OVER THE REGION TONIGHT AND EARLY
TOMORROW WITH DEEPER MOISTURE MOVING INTO THE AREA DURING THE AFTERNOON.
A COLD FRONT IS THEN EXPECTED TO MOVE ACROSS THE AREA ON TUESDAY
WITH DRY AND UNSEASONABLY COOL HIGH PRESSURE SPREADING OVER THE
REGION IN THE FRONTS WAKE.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 440 PM EDT SUNDAY...MINOR UPDATES TO THE FORECAST WERE MADE TO
INCREASE SKY COVER OVER THE SOUTHEAST TWO THIRDS AS A MORE ROBUST
CUMULUS FIELD HAS DEVELOPED IN LATE DAY HEATING...WITH SFC DEWPOINTS
IN THE 50S. GUSTS HAVE BEEN INCREASED SLIGHTLY AS WELL THROUGH 6 PM
WITH FAIRLY DEEP MIXING.

OTHERWISE...THE UPSTREAM LONGWAVE TROUGH CONTINUES TO DIG ACROSS THE
PLAINS WHILE SURFACE CYCLOGENESIS DEEPENS A POTENT SURFACE WAVE OVER
THE OZARKS. TO THE E...HIGH PRESSURE OVER THE WRN ATLANTIC CONTINUES
TO YIELD SOUTHERLY FLOW WITH STEADY MOISTURE ADVECTION FROM BOTH
THE ERN GULF AND WRN ATLANTIC SOURCE REGIONS. UPPER LEVEL HEIGHTS
WILL BEGIN TO FALL THIS EVENING AS THE AFORE MENTIONED WAVE
APPROACHES FROM THE W. GUIDANCE SEEMS TO AGREE ON WEAK/MODERATE
ISENTROPIC UPGLIDE IN ASSOCIATION WITH AN ATLANTIC SEA BREEZE AS
EVIDENT ON NAM12 295K SURFACE CHARTS. AT THE SAME TIME...LOW LEVEL
FLOW WILL BE INCREASING AS THE PRESSURE GRADIENT TIGHTENS DUE TO
THE APPROACHING SURFACE CYCLONE. THIS COMBINED WITH INCREASING
MOISTURE IN THE LOW LEVELS AND POTENTIAL ISENTROPIC UPGLIDE WILL
INCREASE THE PROBABILITY OF SHOWERS OVERNIGHT...MAINLY ACROSS THE
NE GA AND THE SW NC MOUNTAINS DUE TO UPSLOPE ENHANCEMENT.

SHOWER POTENTIAL WILL SPREAD FURTHER E THROUGH MORNING AND INTO
MONDAY AFTERNOON AS THE UPGLIDE REGIME IMPROVES AND INSTABILITY
BUILDS. WILL RAMP POPS UP TO SOLID CHANCE LEVELS BY MID/LATE MORNING
ACROSS THE BALSAMS/SMOKIES BEFORE CATEGORICAL POPS PREVAIL BY
MIDDAY. TO THE E...POPS WILL RAMP UP FROM SLIGHT CHANCE LEVELS
THROUGH THE AFTERNOON. TEMPERATURES TOMORROW WILL BE CAPPED BY
MOSTLY CLOUDY SKIES...AS HIGHS STRUGGLE TO TOP THE MID 60S ACROSS
THE HIGH TERRAIN AND LOWER 70S IN THE PIEDMONT. WITH THAT SAID...THE
INCREASING SOUTHERLY FLOW WILL ALLOW FOR DEWPOINTS TO SURGE A FEW
DEGREES LEADING TO AT LEAST SOME WEAK INSTABILITY THROUGH THE
PROFILE. A FEW THUNDERSTORMS CANNOT BE RULED OUT WITH BRIEF HEAVY
RAINFALL...GUSTY WINDS...AND CLOUD TO GROUND LIGHTNING BEING THE
PRIMARY THREATS. NOT EXPECTING ANY SEVERE WEATHER THROUGH THE NEAR
TERM PERIOD AS SHEAR PROFILES DO NOT IMPROVE UNTIL LATER.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 215 PM SUNDAY...WARM SECTOR WIND SHEAR WILL BECOME MORE
FAVORABLE FOR CONVECTIVE ORGANIZATION MONDAY NIGHT...AS STRONG SHORT
WAVE TROUGH APPROACHES THE AREA FROM THE TENN VALLEY. INSTABILITY
WILL (AS USUAL) BE THE PRIMARY LIMITING FACTOR IN TERMS OF THE
SEVERE WEATHER POTENTIAL. HOWEVER...THE SHORT TERM MODELS (WITH
CONSIDERABLE SUPPORT FROM SREF GUIDANCE) DEPICT SOME DEGREE OF
SURFACE AND/OR MIXED LAYER CAPE TO COINCIDE WITH A PERIOD OF
STRONGLY LOOPED HODOGRAPHS...ESP LATE MON EVENING/EARLY IN THE
OVERNIGHT PERIOD. CONSIDERING THE POTENTIAL FOR FRONTAL CONVECTION
TO RUN OUT AHEAD OF THE FRONTAL ZONE...AS WELL AS THE POTENTIAL FOR
WARM SECTOR INITIATION...THERE DOES APPEAR TO BE A MODEST THREAT FOR
SEVERE CONVECTION DURING THIS TIME FRAME.

BY THE PRE-DAWN HOURS TUE MORNING...FORECAST SOUNDINGS DEPICT
VEERING LOWER LEVEL WIND PROFILES AS THE FRONT APPROACHES THE REGION
FROM THE TENN VALLEY. AT THIS POINT...IT IS INCONCLUSIVE AS TO WHAT
DEGREE OF SEVERE WEATHER THREAT WILL ACCOMPANY ANY CONVECTION ALONG
THE FRONT PROPER AS IT MOVES INTO OUR AREA TUE MORNING. THIS IS ESP
TRUE CONSIDERING THE TIME OF DAY...BUT ALSO CONSIDERING THE FACT
THAT MUCH OF THE FRONTAL FORCING IS ALIGNED WITH THE COLDER AIR. IN
FACT...THE BEST BOUNDARY LAYER CONVERGENCE REMAINS WEST OF THE
SURFACE-BASED INSTABILITY AXIS UNTIL PERHAPS THE FRONT SURGES ACROSS
THE PIEDMONT LATER IN THE DAY. THE UPSHOT IS THAT IT APPEARS THE
BEST CHANCES FOR SEVERE WEATHER THROUGH THIS EVENT WILL BE FROM
TOMORROW AFTERNOON THROUGH THE EARLY PORTION OF THE OVERNIGHT (WITH
ANY ORGANIZED PRE-FRONTAL CONVECTIVE CLUSTERS...AND PERHAPS SOME
DISCRETE CELLS)...AND AGAIN FROM LATE TUE MORNING THROUGH TUE
AFTERNOON EAST OF THE MTNS. THE MAIN THREATS WOULD BE FROM DAMAGING
WINDS AND ISOLATED TORNADOES DURING THESE WINDOWS.

OTHERWISE...CATEGORICAL POPS WILL GRADUALLY SPREAD FROM WEST TO EAST
ACROSS THE FORECAST AREA MON NIGHT...PEAKING AT AROUND 12Z TUE...
BEFORE HIGHER POPS SHIFT TO THE EASTERN ZONES TUE AFTERNOON. COLDER
AIR WILL BEGIN SURGING INTO THE AREA BEFORE PRECIP COMES TO AN END.
IN FACT...SHORT TERM MODEL FORECAST SOUNDINGS FOR TUE FEATURE A VERY
IMPRESSIVE BOUT OF COLD ADVECTION ACROSS THE AREA FROM LATE MORNING
THROUGH THE AFTERNOON...WITH TEMPS FALLING BY AS MUCH AS 20 DEGREES
ACROSS MUCH OF THE AREA BETWEEN MORNING AND SUNSET. GUSTY NW WINDS
CAN BE EXPECTED IN THE MOUNTAINS DURING THE AFTERNOON AND EVENING...
WITH GUSTS IN EXCESS OF 40 MPH LIKELY IN MANY AREAS.

THE MAIN CONCERN WILL THEN SHIFT TO THE FROST/FREEZE POTENTIAL FOR
THE REMAINDER OF THE PERIOD...AS AN UNSEASONABLY DRY AND COLD AIR
MASS SETTLES OVER THE REGION. AN ADVECTIVE FREEZE APPEARS TO BE MORE
OR LESS A SLAM DUNK OVER THE MTNS TUE NIGHT. HOWEVER...GUIDANCE IS
TRENDING COOLER FOR SOME AREAS EAST OF THE MTNS...PARTICULARLY THE
I-40 CORRIDOR...AND PLAN TO ADD A MENTION OF POSSIBLE FREEZING
CONDITIONS IN THOSE AREAS TO THE HWO. BY WED NIGHT...THE AIR MASS
BEGINS TO MODIFY...AS HEIGHTS RISE STRONGLY IN RESPONSE TO MAJOR
WESTERN CONUS HEIGHT FALLS. WHILE AREAS OF FROST ARE POSSIBLE... THE
FREEZING POTENTIAL IS A BIT MORE UNCERTAIN ATTM.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 2 PM SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z ON
THURSDAY WITH BROAD UPPER TROFFING DEEPENING OVER THE NORTHERN AND
CENTRAL ROCKIES AS THE SE CONUS REMAINS UNDER PERSISTENT SWLY UPPER
FLOW. OVER THE NEXT COUPLE OF DAYS...THE LONG RANGE MODELS BEGIN TO
DIVERGE A FAIR AMOUNT WITH THE EVOLUTION AND PROGRESSION OF THE
UPPER TROF. THE NEWEST RUN OF THE GFS MAINTAINS A CONSIDERABLY
BROADER TROF THAT DEVELOPS INTO A CLOSED H5 LOW BY EARLY FRI...WHILE
THE 00Z ECMWF AND THE CMC MAINTAIN AN OPEN WAVE THAT PROGRESSES
FARTHER SOUTHWARD AND APPROACHES THE FCST AREA ABOUT 12 HRS SOONER
THAN THE GFS. BY 12Z SAT...THE ECMWF HAS THE TROF AXIS DIRECTLY OVER
THE CWFA WHILE THE GFS STILL MAINTAINS A COHERENT CLOSED H5 LOW THAT
REMAINS WELL TO OUR NORTH OVER THE GREAT LAKES. DURING THE REMAINDER
OF THE PERIOD...THE ECMWF TRIES TO REESTABLISH UPPER RIDING OVER THE
SE REGION WHILE THE GFS MAINTAINS BROAD UPPER TROFFING.

AT THE SFC...A STRONG HIGH WILL BE CENTERED OVER THE NE NEW ENGLAND
BRINGING SETTING UP A SIGNIFICANT COLD AIR WEDGE BY MIDWEEK.
ALTHOUGH THE MODEL GUIDANCE DOES DIVERGE LATER IN THE FCST
PERIOD...IT DOES SUGGEST THAT THE WEDGE WILL PROBABLY HANG ON WELL
INTO FRI. IT ALSO SUGGESTS THAT BY THE END OF THE PERIOD NEXT
SUN...ANOTHER HIGH WILL MOVE INTO THE REGION FROM THE NW AND DRY
THINGS OUT AGAIN. THE MAIN PERIOD IN QUESTION WILL BE FRI AND SAT.
THE GFS SPINS UP A LOW OVER THE SOUTHERN PLAINS BY EARLY FRI AND
MOVES IT STRAIGHT TO THE GREAT LAKES WITH ITS ASSOCIATED FRONT
CROSSING THE CWFA BY EARLY SAT. THE CMC DOES SOMETHING SIMILAR BUT
IS ABOUT 12 TO 24 HRS SLOWER. THE ECMWF...HOWEVER...TRIES TO SPIN UP
A WEAK LOW JUST OFF THE CAROLINA COAST DURING THE SAME TIME PERIOD.
AS FOR THE SENSIBLE FCST...THINGS SHOULD BE DRY AND UNSEASONABLY
COOL ON EARLY IN THE PERIOD. PRECIP CHANCES RAMP UP  ON FRIDAY WITH
THE HIGHEST VALUES LATE FRI THRU SAT AFTERNOON. FOR THE TIME
BEING...I KEPT THEM AT HIGH END CHANCE UNTIL MORE CONSISTENCY IS
EVIDENT FROM THE MODELS. AT PRESENT...THERE IS LITTLE IN THE WAY OF
INSTABILITY ON FRI/SAT BUT A FEW TS CANNOT BE RULED OUT ESPECIALLY
IN THE SOUTHERN ZONES. TEMPS SHOULD CLIMB THRU THE PERIOD WITH HIGHS
REACHING NORMAL VALUES BY THE END OF THE PERIOD.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
AT KCLT...BKN VFR STRATOCUMULUS WILL PERSIST UNTIL SUNDOWN GIVEN THE
MOISTENING BOUNDARY LAYER...WITH SCT VFR CLOUDS THEN LINGERING
THROUGH THE EVENING HOURS. SOME LOW END SRLY GUSTS HAVE BEEN ADDED
TO THE TAF THROUGH EARLY EVENING WITH MIXING...BUT A STEADIER S WIND
LESS THAN 10 KT IS EXPECTED OVERNIGHT. ANTICIPATE MVFR CIGS
DEVELOPING OVERNIGHT...AND EVENTUALLY IFR CIGS BY DAYBREAK MON...AS
ATLANTIC AND GULF MOISTURE START ARRIVING IN THE TERMINAL FORECAST
AREA. WEAK ISENTROPIC ASCENT ALSO WARRANTS A MENTION OF PROB30 FOR
-SHRA NEAR THE END OF THE PERIOD...WITH CIGS IMPROVING SLIGHTLY TO
PREVAILING LOW VFR BY AROUND 16Z.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE AS VFR PREVAILS THROUGH MID
MORNING...BUT WITH BKN CUMULUS AT THE SC TAF SITES UNTIL EARLY
EVENING. INCREASED LOW LEVEL MOISTURE AND ISENTROPIC ASCENT
OVERSPREAD THE REGION OVERNIGHT...CAUSING CIGS TO LOWER TO MVFR AND
EVENTUALLY IFR AT ALL LOCATIONS WITH THE EXCEPTION OF KHKY...WHERE
LOW MVFR WILL PREVAIL. HANDLED IFR CIGS WITH TEMPOS AT THE SC SITES.
LASTLY...INCLUDED PROB30 AT ALL SITES FOR UPGLIDE -SHRA AROUND
DAYBREAK AND EVENTUALLY PREVAIL -SHRA BR AT KAVL AND KAND NEAR THE
END OF THE TAF CYCLE. SOUTHERLY WINDS WILL REMAIN IN THE 10-12KT
RANGE WITH OCCASIONAL GUSTS POSSIBLE THROUGH THE AFTERNOON WITH
GUSTS SUBSIDING AS THE MIXED LAYER SHRINKS. WINDS WILL PICKUP YET
AGAIN AFTER DAYBREAK MONDAY AT ALL SITES WITH GUSTS RETURNING AT
KHKY.

OUTLOOK...A LOW PRESSURE SYSTEM DEEPENING ACROSS THE CENTRAL AND
SOUTHERN PLAINS WILL CONTINUE PUSHING EAST THROUGH TUESDAY. MOISTURE
AND LIFT ASSOCIATED WITH THIS SYSTEM WILL LIKELY YIELD SHOWERS AND
RESTRICTIVE CONDITIONS MON NIGHT THROUGH AT LEAST TUESDAY MORNING. A
FEW THUNDERSTORMS WILL BE POSSIBLE AS WELL. CONDITIONS WILL THEN
IMPROVE FROM MID WEEK ONWARD AS DRY HIGH PRES SETTLES IN.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-20Z
KCLT       HIGH 100%     HIGH 100%     MED   79%     HIGH  90%
KGSP       HIGH 100%     HIGH 100%     HIGH  84%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     MED   76%     HIGH  97%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  96%
KGMU       HIGH 100%     HIGH 100%     HIGH  84%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH  91%     HIGH  98%

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...JPT
NEAR TERM...CDG/HG
SHORT TERM...JDL
LONG TERM...JPT
AVIATION...CDG/HG






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