Area Forecast Discussion
Issued by NWS Greer, SC

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522
FXUS62 KGSP 010242
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1042 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 1030 PM EDT SATURDAY...WELL...THANK GOODNESS THE RAIN IS
COMING TO AN END ON THE SOUTH SIDE OF CHARLOTTE...WHERE RADAR
ESTIMATES OF STORM TOTAL PRECIPITATION ARE UPWARDS OF 7 INCHES. GSP
STP IS A LITTLE ON THE HIGH SIDE...BUT CERTAINLY LOOKS LIKE A GOOD
SWATH OF 5-6 INCHES. THESE ALL SET UP ON THE BOUNDARY BUT WERE
ENHANCED BY LOW-LEVEL SHEAR...SO EVEN WITH DECREASING INSTABILITY
THE STORMS WERE ABLE TO ANCHOR OVER THE AREA. NOT IN THE CLEAR YET
AS ANOTHER ROUND OF MODERATE RAIN IS MOVING ACROSS THE UPSTATE. HAVE
UPDATED POPS AGAIN TO ACCOUNT FOR TRENDS BUT FOCUS HAS BEEN ON
CURRENT WX SITUATION THIS EVENING.

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 /03Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...ONLY CHANGES TO KCLT 03Z TAF AMD ARE TO
DELAY IFR CIGS ANOTHER HOUR WHILE HOLDING ONTO TEMPO TSRA THROUGH
04Z. OTHERWISE...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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       MED   79%     MED   70%     HIGH  87%     HIGH 100%
KGSP       MED   69%     HIGH  82%     HIGH  82%     HIGH 100%
KAVL       HIGH  85%     HIGH  96%     HIGH  85%     HIGH 100%
KHKY       HIGH  83%     HIGH  90%     HIGH  86%     HIGH  85%
KGMU       HIGH  87%     MED   78%     HIGH  80%     HIGH 100%
KAND       HIGH  89%     HIGH  89%     HIGH  86%     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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