Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 311228
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
828 AM EDT THU JUL 31 2014

.SYNOPSIS...
A RIDGE OF CANADIAN HIGH PRESSURE WILL REMAIN OVER THE AREA INTO
THE WEEKEND AS A FRONT MOVES NORTH TO THE COAST. MOISTURE
INCREASING BETWEEN THESE TWO SYSTEMS WILL INCREAS THE CHANCES OF
WIDESPREAD SHOWERS AND THUNDERSTORMS. CONDITIONS RETURN TO THOSE
MORE TYPICAL OF LATE SUMMER BY THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
1230 UTC UPDATE...POPS AND QPF WERE INCREASED PER RADAR TRENDS IN
THE SC FOOTHILLS...WHERE UPSLOPE FLOW AND MOIST ISENTROPIC UPGLIDE
HAVE RESULTED IN GREATER PRECIPITATION COVERAGE.

AS OF 630 AM EDT THURSDAY...LINE OF UPGLIDE INDUCED SHOWERS ALONG
AND SOUTH OF THE I85 CORRIDOR IN THE WESTERN UPSTATE IS EXPECTED TO
CONTINUE THROUGH MORNING THEREFORE MADE SOME FINE TUNE ADJUSTMENTS
TO POPS.  OTHERWISE...TWEAKED TEMPERATURES AND DEWPOINTS IN THE
EXTREME NEAR TERM AND LEFT THE REMAINDER OF THE FORECAST AS IS FOR
THIS UPDATE.

PREVIOUS DISCUSSION...

AS OF 300 AM EDT THURSDAY...UPPER TROF LOCATED OVER THE EASTERN
UNITED STATES WILL REMAIN IN PLACE WHILE A SHORT WAVE IMPULSE PASSES
THROUGH THE MEAN FLOW.  CURRENTLY...SAID SHORT WAVE IS LOCATED
ACROSS THE CENTRAL PLAINS...PUSHING EAST INTO THE MIDSOUTH.
CONSEQUENT CIRRUS SHIELD CONTINUES TO ADVECT DOWNSTREAM ACROSS THE
SOUTHERN APPS LEADING TO PARTLY/MOSTLY CLOUDY SKIES THIS MORNING.

MEANWHILE...SURFACE WARM FRONT CONTINUES TO SPREAD NORTHWEST ACROSS
THE MIDLANDS OF SC...SPILLING INTO THE FORECAST AREA BY MID/LATE
MORNING LEADING TO INCREASING LOW LEVEL CLOUDINESS.  A CONVERGENCE
AXIS ALONG THE LEADING EDGE OF THIS INTRUDING WARM FRONT...AND WEAK
WEDGE LIKE SURFACE RIDGE WILL CONTINUE TO PROMOTE WEAK SHOWER
ACTIVITY EARLY IN THE DAY.  PRECIPITATION CHANCES WILL INCREASE
THROUGH THE DAY HOWEVER AS MODERATE UPGLIDE ATOP WEDGE BOUNDARY
COMBINES WITH WEAK ELEVATED INSTABILITY TO SUPPORT CONVECTION.

FORECAST WILL INITIATE THIS MORNING WITH SLIGHT CHANCE POPS ACROSS
THE UPSTATE...NORTHEAST GA...AND THE NC FOOTHILLS/PIEDMONT...WITH
POPS INCREASING TO LOW END LIKELY LEVELS NEAR THE END OF THE
PERIOD.  AS FOR THE MOUNTAINS...ABOVE MENTION UPGLIDE/INSTABILITY
WILL BE ENHANCED AS WEAK EASTERLY UPSLOPE FLOW COMMENCES LEADING TO
HIGHER POPS ACROSS THE TERRAIN.  FOR THE MOUNTAINS...FORECAST WILL
FEATURE CHANCE LEVEL POPS INITIALLY WITH CATEGORICAL POPS TO ROUND
OUT THE FORECAST.  DUE TO RETURN FLOW OF MOISTURE THERE WILL BE SOME
ELEVATED INSTABILITY ACROSS THE REGION TODAY PER FORECAST
SOUNDINGS.  THEREFORE CANNOT RULE OUT AN ISOLATED THUNDERSTORM WITH
A PRIMARY THREAT OF CLOUD TO GROUND LIGHTING ESPECIALLY WHEN ABOVE
MENTIONED SHORT WAVE ENERGY MOVES IN LATE.  SPEAKING
OF...PRECIPITATION RATES WILL ALSO IMPROVE LATE TONIGHT INTO THE
OVERNIGHT WITH THE HIGHEST AMOUNTS RESIDING ALONG THE BLUE RIDGE
WHERE UPWARDS OF 1 TO 1.5 INCHES IS POSSIBLE.  TEMPERATURES THROUGH
THE PERIOD WILL REMAIN 8-10 DEGREES BELOW NORMAL AS RADIATIONAL
HEATING IS LIMITED DUE TO ABUNDANT SKY COVER AND PRECIPITATION.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 330 AM...IT IS LOOKING MORE AND MORE LIKELY THAT THE FIRST
PART OF THE WEEKEND WILL BE WET. SWLY UPPER FLOW INCREASES THRU THE
PERIOD AS A TROF AXIS TO THE WEST SHARPENS AND THE ATLANTIC
SUB-TROPICAL ANTI-CYCLONE MOVES WEST TOWARD THE COAST. SHORT WAVES
MOVE THRU THE FLOW AND ACROSS THE AREA KEEPING Q-VECTOR CONVERGENCE
IN PLACE. IN ADDITION...UPPER LEVEL DIVERGENCE REMAINS OVER THE AREA
AS THE RIGHT ENTRANCE REGION OF AN UPPER JET BECOMES PARKED NEARBY.
A SERIES OF H85 LOWS MOVE OVER THE AREA BRINGING PERIODS OF SELY LOW
LEVEL FLOW. THESE KEEP LOW LEVEL AND DEEP MOISTURE ACROSS THE AREA
AS WELL. BEST POP WILL BE ALONG THE BLUE RIDGE WHERE UPSLOPE FLOW
MAXIMIZES. HOWEVER...LIKELY POP WILL BE FEATURED ALL AREAS GIVEN THE
MOISTURE AND FORCING. SCT TSRA SHUD ALSO DEVELOP...MAINLY ALONG AND
SOUTH OF I-85 AS ELEVATED INSTABILITY DEVELOPS. FCST HODOGRAPHS SHOW
QUITE A BIT OF SPEED AND DIRECTIONAL SHEAR DEVELOPS. RIGHT NOW...
INSTABILITY REMAINS RELATIVELY WEAK AND ELEVATED...BUT WILL HAVE TO
KEEP AN EYE ON THIS.

SATURDAY WILL BE SIMILAR TO FRIDAY EXCEPT FOR THE WEAKENING SFC
RIDGE LEADING TO INCREASED INSTABILITY AND BETTER CHC OF SCT TSRA
ACROSS THE AREA. ALTHOUGH INSTABILITY WILL BE GREATER...SHEAR WILL
BE MUCH LESS. STILL TOO EARLY TO TELL IF AREAS OF HEAVY RAIN WILL
DEVELOP EITHER DAY...BUT IT CANNOT BE RULED OUT. HIGHS FRIDAY WILL
BE 10 TO 15 DEGREES BELOW NORMAL...THEN RISE ABOUT 5 DEGREES ON SAT.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 340 AM...THE NRN PART OF THE UPPER TROF SLIDES EAST OF THE
AREA LEAVING A WEAK UPPER LOW OVER THE SERN US. THE UPPER LOW THEN
SLIDES ACROSS THE AREA LEAVING ZONAL FLOW IN PLACE. AT THE SFC... A
WEAK FRONT OR BAROCLINIC BOUNDARY REMAINS ALONG THE COAST WITH WEAK
HIGH PRESSURE OVER THE APPALACHIANS. LIKELY POP ON SUN DROPS TO
DIURNAL CHC POP FOR THE REST OF THE PERIOD. HIGHS SUN AROUND 10
DEGREES BELOW NORMAL SLOWLY RISE TO NEAR NORMAL BY THE END OF THE
PERIOD.

&&

.AVIATION /13Z THURSDAY THROUGH MONDAY/...
AT KCLT...A MIXTURE OF VFR/MVFR CONDITIONS WILL PREVAIL THROUGH THIS
TAF PERIOD.  INITIALIZED TAF WITH BKN LOW/MID LEVEL CIG WHICH
CARRIES THROUGH 22Z.  AT THAT TIME...MARGINAL UPGLIDE COMBINED WITH
WEAK INSTABILITY COULD PRODUCE SHRA/TSRA AT THE AIRFIELD...THEREFORE
OPTED FOR TSRA PROB30 FROM 22-02Z.  EXPECTING CIGS TO RECOVER AS
PRECIP SUBSIDES DURING A BRIEF LULL BEFORE UPPER WAVE MOVES IN NEAR
THE END OF THE PERIOD INITIATING SHRA AND MVFR CIGS.  5-8KT
NORTHEASTERLY WINDS WILL PREVAIL THROUGH THE PERIOD WITH AN
OCCASIONAL EASTERLY COMPONENT EARLY ON THIS MORNING.

ELSEWHERE...A MIXTURE OF VFR/MVFR CONDITIONS WILL PREVAIL AT ALL
SITES THROUGH THE PERIOD WITH KAVL ACTUALLY LOWERING TO IFR/LIFR
LEVELS LATE IN THE PERIOD.  LINE OF UPGLIDE INDUCED SHOWERS ACROSS
THE WESTERN UPSTATE WILL LIKELY CONTINUE THROUGH MUCH OF THE MORNING
BEFORE SPREADING AS WEAK DESTABILIZATION OCCURS BY LATE MORNING INTO
THE EARLY AFTERNOON.  THUS...PREVAILED VCSH MENTION AT ALL THE SC
SITES UNDER LOW VFR CIGS THROUGH AROUND NOON WHERE VCSH GIVES WAY TO
VCTS AS THE ATM DESTABILIZES SOMEWHAT.  THERE WILL MOST LIKELY BE A
LULL BY EARLY EVENING AS HEATING IS LOST...HOWEVER WX MENTION
RETURNS LATE IN THE PERIOD AS UPPER WAVE SLIDES EAST PROVIDING WEAK
UPPER SUPPORT TO THE PERSISTENT UPGLIDE REGIME AND CONVERGENCE ALONG
QUASI STATIONARY WARM FRONTAL BOUNDARY.  INCLUDED IFR/LIFR CIGS AT
KAVL LATE IN THE PERIOD AS GUIDANCE IS IN AGREEMENT REGARDING LOW
STRATUS DEVELOPMENT ALONG THE HIGH TERRAIN OVERNIGHT.
LASTLY...REDUCED VSBY AT ALL SITES LATE IN THE PERIOD ASSOCIATED
WITH SHRA AS THE BOUNDARY LAYER MOISTENS AND WINDS SUBSIDE
OVERNIGHT.  WINDS THROUGH THE PERIOD WILL REMAIN LIGHT AND SOUTHERLY
AT KAVL...AND EAST NORTHEASTERLY ELSEWHERE.

OUTLOOK...MOISTURE WILL CONTINUE TO INCREASE THROUGH THE
REMAINDER OF THE WORK WEEK AS A WARM FRONT APPROACHES FROM THE EAST
AND SOUTHEASTERLY FLOW CONTINUES. UNSETTLED WEATHER WITH ENHANCED
PRECIPITATION CHANCES ALONG WITH MORNING FOG/STRATUS ARE EXPECTED
THROUGH THE WEEKEND.

CONFIDENCE TABLE...

            12-18Z        18-24Z        00-06Z        06-12Z
KCLT       HIGH 100%     HIGH 100%     HIGH  96%     HIGH  86%
KGSP       HIGH  92%     HIGH  98%     MED   72%     HIGH  90%
KAVL       HIGH  91%     HIGH  91%     MED   76%     HIGH  87%
KHKY       HIGH 100%     HIGH 100%     HIGH  97%     MED   76%
KGMU       HIGH  92%     HIGH  97%     MED   74%     HIGH  96%
KAND       HIGH  88%     HIGH  80%     MED   79%     HIGH  97%

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...RWH
NEAR TERM...CDG/JAT
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CDG






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