Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 010008
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
808 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 800 PM EDT SATURDAY...ANOTHER ROUND OF UPDATES TO POPS...
MAINLY TO INCREASE THEM ACROSS THE NC PIEDMONT EARLY AND THEN TREND
INCREASING POPS IN FROM THE WEST AS PER RADAR TRENDS IN N GA. STORMS
HAVE REMAINED BELOW SEVERE LEVELS WITH JUST SOME GUSTY WINDS AND
SMALL HAIL. SBCAPE VALUES HAVE REALLY DROPPED OFF AND THE DAMMING IS
STRENGTHENING. OVERALL THOUGH T/TDS ARE IN PRETTY GOOD SHAPE.

OTHERWISE...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 /00Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...WIDESPREAD CONVECTION AROUND THIS EVENING
WITH TSRA MOVING INTO THE KHKY/KCLT AREAS...WITH A BIT OF A BRIEF
LULL ELSEWHERE. HAVE TRIED TO INCORPORATE THIS INTO THE TAFS. IFR
CIGS AT KHKY SHOULD EXPAND WEST AND SOUTHWEST WITH IFR EXPECTED
OVERNIGHT EVERYWHERE EXCEPT POSSIBLY KAND. SHOULD SEE SOME
IMPROVEMENT TO MVFR AND THEN VFR SUNDAY AFTERNOON FOR ALL BUT
KHKY...CURRENTLY EXPECTED TO REMAIN MVFR. ENE TO NE WINDS THIS
EVENING WILL VEER SE OVERNIGHT AND TO SW TOMORROW...THOUGH WITH
STANDARD DOWN-VALLEY COMPONENT AT KAVL. OTHER CONCERN IS TSRA. CAPES
CONTINUE TO DROP OFF OVERNIGHT BUT ENOUGH THAT WE COULD SEE EMBEDDED
TS AT ANY TIME...BUT FOR THE MOST PART KEPT JUST -SHRA BUT TRENDED
TOWARD PROB30 TSRA SUNDAY MID-MORNING...THEN VCTS BY SUNDAY
AFTERNOON. WILL HAVE TO MONITOR FORECAST TRENDS TO UPDATE IN REAL
TIME.

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...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       MED   74%     MED   77%     HIGH  84%     HIGH 100%
KGSP       HIGH  85%     MED   78%     HIGH  81%     HIGH 100%
KAVL       MED   77%     HIGH  99%     HIGH  83%     HIGH 100%
KHKY       HIGH  80%     HIGH  91%     HIGH  86%     HIGH  84%
KGMU       HIGH  90%     MED   75%     HIGH  82%     HIGH 100%
KAND       HIGH  94%     MED   79%     HIGH  88%     HIGH 100%

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/TDP
SHORT TERM...CSH
LONG TERM...SBK
AVIATION...TDP



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