Area Forecast Discussion
Issued by NWS Greer, SC

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287
FXUS62 KGSP 301854
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
254 PM EDT SAT APR 30 2016

.SYNOPSIS...
AN UPPER LOW WILL APPROACH THE AREA WITH A FRONTAL PASSAGE MONDAY
MORNING.  A SECOND MAJOR FRONT AHEAD OF A MASS OF COLD AIR FROM
CANADA IS EXPECTED BY THURSDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 245 PM EDT SATURDAY...AN INTERESTING SURFACE PATTERN
PREVAILS OVER THE REGION AS A WEDGE BOUNDARY CONTINUES TO
HOLD...ACTUALLY PUSHING A BIT FURTHER TO THE SOUTH OVER THE LAST
FEW HOURS...ALL WHILE A WARM FRONT APPROACHES FROM THE SOUTH.
ALOFT...SHORTWAVE VORT ENERGY IS PUSHING THROUGH THE TN VALLEY AT
THIS TIME AND WILL LIKELY PROMOTE FURTHER EXPANSION OF CONVECTION
OVER WESTERN NC THROUGH THE AFTERNOON/EVENING.
CURRENTLY...CONVECTION HAS INITIATED IN THE WARM SECTOR ACROSS
NORTHEAST GA WITH PROPAGATION TAKING SAID CELLS NORTHEAST UP THE
I85 CORRIDOR OVER THE NEXT FEW HOURS. LATEST MESOANALYSIS PROVIDES
AN ILLUSTRATION OF THE WEDGE BOUNDARY LOCATION AS SBCAPE PLOTS
INDICATE A SHARP 500+ JOULES GRADIENT ALONG/SOUTH OF I85 WITH
SURFACE WINDS REFLECTING SUCH WITH ENE FLOW DOMINATING OVER THE NC
PIEDMONT...SOUTHWEST TOWARDS GSP...WITH ESE FLOW FURTHER SOUTH IN
THE WARM SECTOR. THE MAJORITY OF THE FCST AREA REMAINS UNDER THE
MARGINAL RISK FOR SEVERE WX THIS AFTERNOON WITH LARGE HAIL AND
DAMAGING WINDS BEING THE PRIMARY THREAT. WITH THAT...ENHANCED SRH
IN PROXIMITY TO THE WEDGE BOUNDARY COULD YIELD A BRIEF SPIN UP
TORNADO IF CONVECTIVE BOUNDARY INTERACTION OCCURS. WITH DEEP
UPDRAFTS AND PWATS IN EXCESS OF 1.5 INCHES LOCALIZED HEAVY
RAINFALL ADJACENT TO ANY HEAVIER CONVECTION IS ALSO A POSSIBILITY.

MOVING ALONG INTO THE OVERNIGHT...EXPECTING THE OVERALL INTENSITY
AND COVERAGE OF CONVECTION TO DEPLETE AS HEATING IS LOST AND THE
WARM FRONT PUSHES NORTH OF THE AREA THEREBY REMOVING ANY SFC
FOCUSING MECHANISMS.  HOWEVER...GUIDANCE CONTINUES TO FAVOR SHRA AND
PERHAPS TSRA OVER THE MTNS WHERE UPSLOPING WILL ENHANCE UPDRAFTS.
GIVEN THE RAINFALL...ONCE THE CONVECTION WAINS WOULD NOT BE
SURPRISED IF PATCHY/WIDESPREAD FOG CONSUMES MUCH OF THE FCST AREA BY
MORNING.  SUNDAY LOOKS FAIRLY SIMILAR TO TODAY ASIDE FOR THE ENTIRE
FCST AREA BEING FIRMLY IN THE WARM SECTOR.  SHEAR LOOKS A BIT BETTER
AS A PREFRONTAL TROF MOVES INTO THE REGION...WHILE ANOTHER PIECE OF
H5 SHORTWAVE ENERGY DOES THE SAME.  STRONG/SEVERE CONVECTION IS
POSSIBLE ON SUNDAY WITH LARGE HAIL AND DAMAGING WINDS BEING THE
PRIMARY CONCERN AS SFC FLOW WILL BE VEERED THUS RESULTING IN LESS
FAVORABLE TORNADO CONDITIONS.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 1205 PM EDT SATURDAY...UPPER HEIGHTS ATOP THE SE CONUS WILL
BEGIN TO FALL ON MONDAY AS SOUTHERN PLAINS ENERGY TRANSLATES
EASTWARD. THE RECENTLY POSTED OP RUNS OF THE 30/12 UTC NAM/GFS
SUPPORT THE 30/00 UTC ECMWF TREND OF THE MAIN LLVL BAROCLINIC
ZONE LINGERING NEAR OR NW OF THE CWFA. HENCE...IN CONJUNCTION WITH
THE DEVELOPING FAVORABLE UPPER LEVEL DYNAMICS...CHANCES FOR
DIURNALLY ENHANCED DEEP CONVECTION WILL BE INCREASING. INITIAL
THOUGHTS WILL BE FOR ON AN UPWARD BUMP IN TSTM PROBABILITIES MONDAY
AFTERNOON. CONTINUED UNSETTLED BUT LESS WARM WX CONDITIONS ARE
EXPECTED ON TUESDAY GIVEN THE PROGGED SLOW EVOLUTION OF THE MEAN
PATTERN FEATURING BROAD/DEEP SW FLOW AND THE SLOW SE SAGGING OF
ATTENDANT FRONTAL SYSTEM. WILL PLAN AND KEEPING SOLID MID-CHANCE
POP IF NOT AN UPWARD NUDGE TO LIKELY.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 130 PM SATURDAY...THE EXT RANGE WILL FEATURE A DEVELOPING
UNSEASONAL AND BROAD ERN CONUS ULVL TROF. THIS TROF WILL INTERACT
WITH A STATIONARY FRONT TRAPPED IN A DEEP MEAN SW/LY FLOW. THERE ARE
SIGFNT MODELED DIFFERENCES AS TO THE AMOUNT OF S/W ENERGY TRAVERSING
THE TROF...THE DEGREE OF ATL CYCLOGENESIS...THE AMOUNT OF LLVL COLD
AIR MAKING IT TO THE CAROLINAS...TILT OF THE ULVL TROF...AND
AVAILABLE MOISTURE. WITH THIS SAID...WILL MAINTAIN GRIDS CLOSE TO
THE PREVIOUS FCST. SINCE THE SYSTEM IS OUTSIDE THE NORMS FOR THIS
TIME OF YEAR WILL ALSO SIDE MORE WITH THE DYNAMICAL SOLNS AS OPPOSED
TO MOS GUIDANCE.

DO BELIEVE IT WILL BE A FAIRLY ACTIVE PERIOD WITH THE FRONTAL ZONE
BISECTING THE CWFA PROVIDING A FOCUSING MECHANISM FOR -SHRA AND
PERHAPS A COUPLE GENERAL TSTMS WED/THU AFTERNOONS. SOME DRIER AIR
LOOKS TO WORK IN AHEAD OF DEVELOPING OMEGA RIDGE FRI/SAT WHILE THE
SFC LOW PULLS NE OF THE AREA. THIS WILL CONFINE THE BETTER MOISTURE
ACROSS THE NC MTNS AND PERHAPS PRODUCE NON/ACCUM -SNSH THU NIGHT
ACROSS THE HIGHEST ELEVATIONS AS H85 TEMPS DROP TO -2 C ACCORDING TO
THE ECMWF...YET ONLY DOWN TO ARND ZERO GOING BY THE GFS. THU NIGHT
WILL BE THE COLDEST AT THE SFC AS WELL WITH HIGH ELEV TEMPS
DROPPING TO JUST ABOVE FREEZING. THIS SCENARIO WILL BE WATCHED FOR
POSSIBLE FROST/FREEZE CONCERNS. WITH CLOUD COVER LIKELY REMAINING
MCLDY/CLDY AND COOLER CP AIR MIXING BEGINNING THU...MAX TEMPS WILL
REMAIN NEAR NORMAL WED...WITH A DECREASE BY A COUPLE CATS THU/FRI
THEN A RETURN TO NORMAL LEVELS SAT AS SFC RIDGING ENGULFS THE SE
STATES.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AT KCLT...MVFR IMPROVING TO LOW VFR THROUGH THE AFTERNOON.
EXPECTING CURRENT WEDGE INDUCED STRATUS TO RETREAT NE OVER THE NEXT
HOUR ALLOWING FOR MVFR TO SCT OUT.  WINDS WILL BE A BIT TRICKY AS
THE BOUNDARY ITSELF CONTINUES TO HOVER IN THE VICINITY...THUS
STARTED TAF NE...HOWEVER THINK VEERING TO SE IS LIKELY BY MID
AFTERNOON.  CONVECTION IS ALREADY STARTING TO INITIATE TO THE
WEST...AND WILL CONTINUE TO DEVELOP ALONG I85 IN THE UPSTATE IN THE
NEAR TERM.  THUS...CARRIED NO WX MENTION IN THE PREVAILING LINE
BEFORE INTRODUCING A 4HR TEMPO AT 21Z TO ACCOUNT FOR TSRA AND GUSTY
WINDS AS WELL AS MVFR STRATUS.  BEYOND THAT...SCT SHRA WILL REMAIN
IN THE AREA THROUGH AT MIDNIGHT THUS CARRIED SHRA...WITH VCSH
PREVAILING SHORTLY AFTER MIDNIGHT AMIDST LOWERING MVFR THEN IFR
CIGS/VISB.  THESE RESTRICTIONS WILL CARRY UNTIL AROUND DAYBREAK WITH
VISB IMPROVING FIRST...THEN CIGS TO FOLLOW AN HOUR OR SO AFTER
SUNRISE.  BY THAT TIME WINDS WILL BE SOLIDLY OUT OF THE SE BENEATH
MVFR CIGS.

AT KHKY...VERY SIMILAR TO KCLT ABOVE REGARDING AFTERNOON/OVERNIGHT
RESTRICTIONS...HOWEVER WITH SOME TIMING ADJUSTMENTS OF SHRA...WITH
LESS CHANCES FOR TSRA AS THE AIRMASS IS A BIT MORE STABLE.
NEVERTHELESS...UPSTREAM CONVECTION COULD IMPACT THE SITE LEADING TO
AMDS AT A LATER TIME THIS AFTERNOON.

AT KAVL AND THE SC SITES...SIMILAR CONVECTIVE TRENDS TO KCLT ABOVE
HOWEVER WITH SLIGHT TIMING ADJUSTMENTS AS CONVECTION WILL DEVELOP
CLOSER TO THESE SITES.  OTHERWISE...WINDS WILL REMAIN ESE...VEERING
SE OVERNIGHT TO REMAIN THROUGH THE PERIOD.  TEMPOS ARE FAVORED AT
ALL SITES FOR TSRA...WITH VCTS CARRIED THROUGH MUCH OF THE
EVENING/OVERNIGHT...EVENTUALLY GIVING WAY TO SHRA AMIDST IFR
CIGS/VISB...BEFORE NO WX IS MENTIONED JUST AHEAD OF SUNRISE WHEN
RESTRICITIONS IMPROVE.

OUTLOOK...UNSETTLED WEATHER/OCCASIONAL CONVECTION/RESTRICTIONS ARE
EXPECTED TO CONTINUE INTO EARLY NEXT WEEK...AS A FRONT BECOMES
STALLED NEAR THE AREA. DEFINITIVE DRYING DOES NOT APPEAR LIKELY
UNTIL AT LEAST MID-WEEK.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       MED   72%     MED   73%     HIGH  84%     MED   78%
KGSP       HIGH 100%     HIGH  81%     MED   74%     HIGH  85%
KAVL       HIGH  96%     HIGH  85%     HIGH  88%     HIGH  85%
KHKY       MED   73%     HIGH  80%     HIGH  91%     HIGH  86%
KGMU       HIGH 100%     HIGH  90%     MED   70%     HIGH  81%
KAND       HIGH 100%     HIGH  92%     MED   77%     HIGH  85%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...SBK/WJM
NEAR TERM...CDG
SHORT TERM...CSH
LONG TERM...SBK
AVIATION...CDG



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