Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 140237
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1037 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 1030 PM EDT SUNDAY...SLOWLY FALLING TEMPS THIS EVENING ARE
GENERALLY ON TRACK WITH THE FORECAST DESPITE THE THICKENING HIGH
CLOUDS ACROSS THE AREA...AND WITH PESKY STRATOCUMULUS AT 6 TO 8 KFT
ACROSS THE SW HALF. THERE REMAINS STRONG CONSENSUS ON LOW LEVEL
MOISTURE ARRIVING FROM ATLANTIC AND GULF SOURCES TO PROVIDE A LOWER
OVERCAST TOWARD MORNING. ISOLD TO SCT SHOWERS REMAIN POSSIBLE IN THE
SRN MTNS AND ALONG UPSLOPE AREAS LATE TONIGHT.

THE SHOWER POTENTIAL WILL SPREAD FARTHER E THROUGH MON MORNING AND
INTO MON AFTERNOON AS UPGLIDE IMPROVES AHEAD OF THE ADVANCING UPPER
TROUGH AND ASSOCIATED SFC COLD FRONT...AND INSTABILITY BUILDS. POPS
INCREASE TO SOLID CHANCE LEVELS BY MID/LATE MORNING ACROSS THE
BALSAMS/SMOKIES...WITH CATEGORICAL PREVAILING BY MIDDAY. TO THE
E...POPS RAMP UP FROM SLIGHT CHANCE TO SOLID CHC THROUGH THE
AFTERNOON. TEMPERATURES MON AFTN WILL BE CAPPED BY MOSTLY CLOUDY
SKIES...AS HIGHS STRUGGLE TO TOP THE MID 60S ACROSS THE HIGH TERRAIN
AND LOWER 70S IN MUCH OF THE PIEDMONT. INCREASING SOUTHERLY FLOW
WILL DEWPOINTS TO SURGE A FEW DEGREES...AND 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 /03Z MONDAY THROUGH FRIDAY/...
AT KCLT...HIGH LEVEL CLOUDINESS CONTINUES TO ARRIVE AND THICKEN FROM
THE W LATE THIS EVENING. MOS AND MODEL SOURCES AGREE IN DEPICTING
THE NEXT ROUND OF MOISTURE INFLUX AT LOW LEVELS...WITH MVFR CIGS
LIKELY BY 08Z AND THEN IFR LIKELY BY 10Z. SLOW IMPROVEMENT TO LOWER
END VFR IS EXPECTED THROUGH LATE MORNING. WILL CONTINUE TO HOLD OFF
ON ANY SHOWER MENTION UNTIL AFT 16Z...WITH PROB30 FOR TSRA INCLUDED
STARTING 19Z. EXPECT SRLY SFC WINDS AROUND 10 KT...WITH GUSTS
INCREASING TO 20 KT DURING THE AFTERNOON HOURS MONDAY.

ELSEWHERE...CIRRUS CIGS THIS EVENING WILL GIVE WAY TO MVFR CIGS
OVERNIGHT 06Z TO 09Z...WITH AT LEAST BRIEF IFR LIKELY MOST PLACES
AROUND DAYBREAK. SCT SHOWER COVERAGE MAY INCREASE FROM THE SW
OVERNIGHT...BUT WILL HOLD OFF ON ANY MENTION AT THIS POINT UNTIL 13Z
AT KAVL AND CLOSER TO 16Z AT THE FOOTHILL TAF SITES. SLOW
IMPROVEMENT TO LOWER END VFR IS POSSIBLE INTO EARLY AFTN...BUT WITH
ADDITIONAL RESTRICTIONS WITH ANY SHOWERS AND PROB30 TSTMS LATE DAY.
EXPECT SRLY FLOW AROUND 10 KT OR LESS THROUGHOUT...WITH GUSTS CLOSE
TO 20 KT DEVELOPING MON AFTN.

OUTLOOK...WIDESPREAD SHOWERS AND RESTRICTIONS WILL DEVELOP AHEAD OF
A COLD FRONT MONDAY NIGHT THROUGH TUESDAY MORNING. THE FRONT WILL
MOVE EAST OF THE AREA LATE TUESDAY...WITH DRY HIGH PRESSURE SETTLING
IN WED THROUGH LATE WEEK.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       HIGH 100%     HIGH  83%     HIGH  90%     HIGH 100%
KGSP       HIGH 100%     MED   79%     HIGH  88%     HIGH  96%
KAVL       HIGH 100%     MED   79%     HIGH  86%     HIGH  86%
KHKY       HIGH 100%     HIGH  88%     MED   78%     HIGH  94%
KGMU       HIGH 100%     MED   79%     HIGH  91%     HIGH  96%
KAND       HIGH 100%     MED   78%     HIGH  87%     HIGH  96%

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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