Area Forecast Discussion
Issued by NWS Greer, SC

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898
FXUS62 KGSP 200606
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
206 AM EDT WED MAY 20 2015

.SYNOPSIS...
DRY HIGH PRESSURE WILL BUILD ACROSS THE REGION TODAY...WITH BRIEFLY
UNSETTLED WEATHER CROSSING THE FORECAST AREA ON THURSDAY. DRIER
CANADIAN HIGH PRESSURE WILL RETURN TO THE CAROLINAS AND NORTHEAST
GEORGIA FRIDAY AND REMAIN INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 200 AM...FEW CHANGES TO THE EARLY MRNG PERIOD. HAVE ALREADY
SEEN SOME VERY LIGHT FOG COME AND GO AROUND THE AREA...PARTICULARLY
ALONG AND SOUTH OF I-85. DRIER AIR IS FILTERING INTO THE CWFA WITH
DEWPOINTS HAVING DIPPED INTO THE 50S OVER THE MTNS AND FAR NW
PIEDMONT. EXPECTING THE DRYING TO SLOWLY OCCUR FURTHER SE...BUT NOT
SURE IF THIS WILL OCCUR FAST ENOUGH TO PREVENT OCNL PATCHES OF FOG
FROM DEVELOPING. A PATCH OF MIDLEVEL CLOUDS HAS FORMED OVER THE
UPSTATE AHEAD OF THE FRONT...BUT LIKEWISE THESE SHOULD MOVE SWD OR
DISSIPATE AS THE FRONT REACHES THERE.

FOR WEDNESDAY...THE FRONT WILL STALL JUST TO THE SOUTH OF THE AREA.
A WEAK SFC WAVE LOOKS TO DEVELOP/MOVE ALONG THE QUASI-STATIONARY
BOUNDARY ON WEDNESDAY ENHANCING SOUTHERLY UPSLOPE POTENTIAL ACROSS
THE SOUTHWEST ESCARPMENT.  THUS THE FCST FEATURES SLIGHT TO LOW END
CHANCE LEVEL POPS OVER THE UPPER FRENCH BROAD VALLEY...WITH AN
ADDITIONAL MENTION ACROSS THE SOUTHERN TIER OF THE CWFA ADJACENT TO
THE FRONTAL AXIS ITSELF.  SOUNDINGS LOOK RATHER UNIMPRESSIVE FOR
WEDNESDAY THEREFORE NOTHING MORE THAN GARDEN VARIETY SHOWERS...WITH
PERHAPS A FEW RUMBLES OF THUNDER ARE FCST.  TEMPERATURES ON
WEDNESDAY WILL REMAIN ABOVE NORMAL DESPITE THE FROPA...ALBEIT LESS
HUMID AS DEWPOINTS IN THE LOWER TO MID 50S ARE FCST OVER THE
PIEDMONT REGIONS WITH 40S FCST OVER THE MTNS.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AS OF 2 PM TUESDAY...ANOTHER AREA OF HEIGHT FALLS WILL OVERSPREAD
THE EASTERN CONUS DURING THE EARLY PART OF THE SHORT TERM...WHICH
WILL ACT TO FINALLY SURGE THE COLD FRONT/CP AIR MASS THROUGH THE CWA
BY THE END OF THE WEEK. IN THE INTERIM...CHANCES FOR CONVECTION WILL
INCREASE AHEAD OF THIS SURGE BEGINNING LATE WED NIGHT/EARLY THU.
SHORT TERM MODELS INDICATE NO CLEAR CONSENSUS AS TO HOW HIGH THE
PROBABILITY OF CONVECTION WILL BE DURING THIS TIME...AS THE NAM
REMAINS QUITE A BIT MORE MOIST AND SOMEWHAT MORE UNSTABLE THAN OTHER
GUIDANCE. THE MAIN LIMITING FACTOR IN SUSTAINING GOOD COVERAGE OF
CONVECTION WILL BE TIMING...AS THE BEST LIFT AND MOISTURE MAY BE
EAST OF THE AREA BY THE TIME THE ATMOSPHERE REACHES PEAK
DESTABILIZATION THU AFTERNOON. POPS WILL THEREFORE BE KEPT IN THE
30-40 PERCENT RANGE.

DRIER/CONVECTION-FREE WEATHER AND MORE SEASONAL TEMPS ARE EXPECTED
BY FRIDAY...AS SURFACE RIDGE EXTENDS TO THE SOUTHEAST COAST BY
12Z.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 215 PM EDT TUESDAY...A BROAD ULVL TROF WILL PUSH OFF THE EAST
COAST SAT AND MAKE WAY FOR A SIGFNT PATTERN CHANGE OVER THE WEEKEND.
WITH THE HUDSON BAY LOW MAINTAINING AREAS OF LOW PRESSURE OVER ERN
CAN...A STRONG UPPER RIDGE WILL BUILD ACROSS THE CENTRAL PLAINS AND
SHIFT EAST OVER THE ERN CONUS THROUGH THE PERIOD. GOOD CONFIDENCE IS
HAD IN THE FCST WITH THE OP MODELS SHOWING SIMILAR TIMING AND
STRENGTH WITH THIS RIDGE THRU MON. SOME VARIANCES ARE NOTED WITH 12Z
GFS BREAKING DOWN THE RIDGE SEVERAL HRS BEFORE THE 00Z ECMWF...BUT
ALL IN ALL...THE SENSIBLE WX WILL BE RATHER PLEASANT AND
NON/THREATENING WITH INCREASING WARMTH.

NO MAJOR CHANGE WERE MADE TO THE FCST GRIDS WITH THE BIGGEST CHANGE
RESULTING IN LOWERING SKY/POP SUN INTO MON. THE LATEST GUIDANCE
TRENDS HAVE EXTENDED THE WRN PORTION OF THE SFC RIDGE WHILE STRONG
SUBSIDENCE DOMINATES THE REGION. THIS WILL FORCE SIGFNT GOM MOISTURE
FLUX WEST OVER THE DEEP SOUTH THROUGH MOST OF THE PERIOD AND ALSO
MAINTAIN A STABLE AIRMASS OVER THE CWFA. SOME AFTERNOON -SHRA ARE
POSSIBLE WITH MTN TOP CONVERGENCE SAT THRU MON...BUT ALL IN ALL THE
ATMOS WILL REMAIN STRONGLY CAPPED AND ALLOW ONLY FAIR WX CU AND
PASSING CI. THINGS CHANGE LATE MON INTO TUE AS THE BERMUDA HIGH
BREAKS DOWN AND ALLOWS INCREASING UPSLOPE FLOW AND ADDED ATL
MOISTURE IN A MORE UNSTABLE ENVIRONMENT. THUS...POPS FOR NEW DAY 7
WERE INTRODUCED AT LOW/MID CHANCE MTNS/FTHILLS AND SW/RN
ZONES...WITH ISOL ACTIVITY PROBABLE EAST. THUNDER INITIATION SHOULD
BE LATE DAY FOCUSING ON THE HIGHER TERRAIN. MAX TEMPS WILL INCREASE
THROUGH THE PERIOD IN GOOD INSOL EACH DAY. STARTING AT AROUND NORMAL
SAT AND INCREASING BY 8-10 DEGREES BY TUE.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...A NEARLY STALLED COLD FRONT REMAINS JUST NORTH OF THE
FIELD. DRIER AIR WILL FILTER IN SLOWLY EARLY THIS A.M. AS IT SAGS
THRU...BUT IT IS QUESTIONABLE WHETHER THIS WILL OCCUR FAST ENOUGH TO
OUTPACE COOLING AND ELIMINATE FOG RISK. SO INCLUDED A TEMPO TO BRING
ATTENTION TO THE CHANCE. HOWEVER EXCEPT FOR THAT VFR SHOULD CONTINUE
THRU THE PERIOD. LOOKS LIKE THE DRIER AIR WILL BE UNSUPPORTIVE OF
DEEP CONVECTION TODAY...SO JUST EXPECTING A FEW HIGH BASED CU TO
BREAK OUT. WINDS WILL SHIFT FROM NE TO SE IN THE AFTN. TONIGHT...A
WEAK AREA OF LOW PRESSURE PASSING ALONG A SECONDARY COLD FRONT WILL
BRING A VFR CIG...AND AN OUTSIDE CHANCE OF A SHOWER WHICH WILL NOT
BE MENTIONED AT THIS ISSUANCE.

ELSEWHERE...DEWPT DEPRESSIONS REMAIN SMALL OVER MUCH OF THE REGION
AS OF 06Z...THOUGH DRIER AIR IS BEGINNING TO MAKE INROADS BEHIND A
COLD FRONT. THAT FRONT IS NOW SETTLED OVER SC. PATCHY MIDLEVEL
CLOUDS WILL LINGER THIS MRNG OVER THE UPSTATE TAF SITES AS A RESULT.
IF APPRECIABLE DRYING DOES NOT MOVE IN FAST ENOUGH SOME OCNL MVFR
VSBYS MIGHT DEVELOP...HENCE TEMPOS IN SOME OF THE TAFS NEAR SUNRISE.
CONVECTION IS EXPECTED TO REMAIN ISOLATED TODAY IN THE DRIER AIRMASS
AND CHANCES AT THE SITES ARE LOW ENOUGH TO OMIT. WINDS WILL VEER TO
SE THIS AFTN...EXCEPT AT KAVL WHICH IS MORE LIKELY TO REMAIN NW.
INCREASING CLOUDS CAN BE EXPECTED THIS EVENING AHEAD OF A INCOMING
LOW.

OUTLOOK...A WEAK WAVE SLIDING ALONG THE OLD FRONTAL AXIS WILL CROSS
THE AREA THURSDAY...WITH CHANCES OF SHRA AND AFTN TSRA RETURNING.
HIGH PRESSURE BUILDS OVER THE SOUTHEAST AND DRY WX RETURNS FOR THE
UPCOMING WEEKEND...LIKELY LASTING INTO EARLY NEXT WEEK.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  97%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH  94%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  94%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  97%     HIGH 100%     HIGH 100%     HIGH 100%

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...SBK
NEAR TERM...CDG/WIMBERLEY
SHORT TERM...JDL
LONG TERM...SBK
AVIATION...WIMBERLEY



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