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Area Forecast Discussion

152
FXUS62 KGSP 300252
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1052 PM EDT WED JUL 29 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL APPROACH THE AREA FROM THE NORTHWEST ON
THURSDAY AND SETTLE SOUTHEAST OF THE REGION ON FRIDAY. THE FRONT AND
ASSOCIATED DEEPER MOISTURE WILL LIKELY REMAIN CONFINED TOWARD THE
SOUTHEAST COASTLINE THROUGH THE WEEKEND...WITH SLIGHTLY COOLER
TEMPERATURES EXPECTED OVER THE FORECAST AREA. LOW LEVEL MOISTURE
WILL GRADUALLY RETURN EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 1045 PM EDT WEDNESDAY...HEATING LOSS HAS ALLOWED FOR THE VAST
MAJORITY OF CONVECTION TO DIMINISH AS FCST WITH MOST CAM GUIDANCE
FAVORING A FAIRLY QUIET OVERNIGHT.  THE ONLY POSSIBLE WRINKLE COULD
BE THE EVENTUAL TRACK OF THE ONGOING CONVECTIVE COMPLEX ACROSS
SOUTHEAST KY MOVING INTO MIDDLE/EAST TN.  LATEST SPC MESOANALYSIS OF
CAPE FIELDS ALONG WITH OOZ NAM CORFIDI VECTORS DIRECT THIS
CONVECTION TO THE WEST.  THAT SAID...DID KEEP CHANCE POPS ALONG THE
TN LINE TO ACCOUNT FOR ANY DEVIATION.  WILL PULL ANY AND ALL THUNDER
WORDING FROM THE HWO AS THE ATMOSPHERE BECOMES INCREASINGLY STABLE
AND ALSO DUE TO THE LACK OF ANY RECENT LIGHTNING STRIKES ANYWHERE IN
THE CWFA.  OTHER THAN THAT...AM EXPECTING AT LEAST PATCHY FOG
OVERNIGHT ACROSS THE REGION WITH PERHAPS SOME AREAS OF DENSE FOG
IN/AROUND THE MOUNTAINS VALLEYS...AND ALSO WHERE ANY SUBSTANTIAL
AMOUNTS OF EARLIER RAINFALL OCCURRED.  BEYOND THAT...TWEAKED
TEMPS/DEWS/SKY TO ACCOUNT FOR MOST RECENT OBS/SAT AND LEFT THE
REMAINDER OF THE FCST UNCHANGED.

PREVIOUS DISCUSSION...

AS OF 225 PM...RADAR SHOWS SCT SHOWERS/THUNDERSTORMS ALIGNED ALONG
THE BLUE RIDGE AND ALSO OVER THE SOUTHERN UPSTATE ALONG AN AXIS OF
HIGHER CAPE. CELLS EXHIBITING ONLY SLOW MOVEMENT TO THE SE. WITH
PRECIP. WATER AROUND 2 INCHES...LOCALLY HEAVY RAIN/FLOODING IS THE
MAIN THREAT THIS AFTERNOON. CAMS INDICATE THAT SOME SCT CONVECTION
MAY LINGER INTO THE EVENING HOURS...BUT IT SHOULD DISSIPATE BY
MIDNIGHT.

IN REGARD TO THE BIG PICTURE FOR THE SHORT TERM. AN UPPER LOW
DEEPENING OVER THE HUDSON BAY WILL PROMOTE FALLING HEIGHTS ACROSS THE
EASTERN U.S. THIS WILL DRIVE A COLD FRONT SE WHICH WILL APPROACH THE
NC MOUNTAINS BY 12Z THURSDAY. THE FRONT WILL THEN PROCEED TO CROSS
THE WESTERN CAROLINAS AND NE GA ON THURSDAY.

IN REGARD TO THE SENSIBLE WEATHER...THE OVERNIGHT WILL FEATURE
PARTLY CLOUDY AND HUMID CONDITIONS WITH SOME LOCALLY DENSE VALLEY
FOG DEVELOPING IN THE MOUNTAINS AFTER MIDNIGHT...AND MAINLY JUST
LIGHT FOG OUTSIDE THE MOUNTAINS. SOME SHOWERS/STORMS ASSOCIATED WITH
THE APPROACHING COLD FRONT MAY REACH THE MOUNTAINS EARLY THURSDAY
MORNING...SO HAVE POPS INCREASING INTO THE CHANCE CATEGORY THERE.

FRONTAL CONVERGENCE COMBINED WITH THE FALLING HEIGHTS SHOULD LEAD TO
SCT TO NUMEROUS THUNDERSTORMS DEVELOPING ACROSS THE AREA DURING
THURSDAY WITH THE BEST COVERAGE DURING THE AFTERNOON OUTSIDE THE
MOUNTAINS. STRONG HEATING AND IMPROVING LAPSE RATES MAY SUPPORT A
FEW SEVERE STORMS THURSDAY AFTERNOON. SPC HAS MOST OF THE AREA
OUTSIDE THE MOUNTAINS IN A MARGINAL RISK FOR THURSDAY. TEMPERATURES
WILL REMAIN ABOVE CLIMO WITH LOWS IN THE 60S MOUNTAINS TO LOW 70S
ELSEWHERE...AND HIGHS FROM THE MID 80S MOUNTAINS TO THE LOWER TO MID
90S ELSEWHERE.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM WEDNESDAY...THE BIG STORY FOR THE SHORT TERM PERIOD
WILL BE THE ESTABLISHMENT OF AN EASTERN LONG WAVE TROUGH...WITH THE
AXIS OF SAID TROUGH EXPECTED TO SET UP ALONG THE EAST COAST BY EARLY
IN THE PERIOD. THIS SHOULD ALLOW THE FRONTAL BOUNDARY...AND
ATTENDANT CONVECTION TO BE CARRIED SOUTHEAST OF THE FORECAST AREA
THURSDAY EVENING. WHILE THICKNESS VALUES WILL NOT CHANGE MUCH IN THE
WAKE OF THE BOUNDARY...ESSENTIALLY RESULTING IN NEAR-CLIMO TEMPS
THROUGH THE PERIOD...THE MAIN IMPACT WILL BE THE INTRODUCTION OF AN
UNSEASONABLY DRY AIR MASS. IN FACT...DEWPOINTS MAY MIX OUT WELL INTO
THE 50S FRI AFTERNOON. THE RESULT WILL BE VIRTUALLY NO POSITIVE
BUOYANCY... AS DEPICTED BY THE LATEST RUNS OF THE NAM AND THE GFS.
POPS WILL THEREFORE BE FEATURES WELL BELOW CLIMO...AND IN FACT BELOW
20 PERCENT ACROSS THE MAJORITY OF THE FORECAST AREA FRI AFTERNOON
AND EVENING. NOT MUCH CHANGE IN THE AIR MASS IS ANTICIPATED THROUGH
SATURDAY...AND POPS REMAIN AT 20 PERCENT OR LESS DURING THE
AFTERNOON AND EVENING. OVERALL...IT/S SHAPING OUT TO BE A DECENT
WEEKEND AS FAR AS EARLY AUGUST GOES.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 205 PM WEDNESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
SUNDAY WITH BROAD UPPER TROFFING OVER THE EASTERN CONUS AND BROAD
UPPER RIDGING IN PLACE OVER THE WESTERN CONUS. THIS PATTERN IS
EXPECTED TO REMAIN IN PLACE THROUGH MOST OF THE PERIOD WITH SOME
DEAMPLIFICATION OF THE UPPER TROF EXPECTED BY THE END OF THE PERIOD
NEXT WEDNESDAY. AT THE SFC...HIGH PRESSURE CENTERED TO OUR NW WILL
BE OVER THE FCST AREA AT THE START OF THE PERIOD AND SHOULD LINGER
INTO EARLY NEXT WEEK...GRADUALLY GETTING WEAKER. THE ECMWF STILL
TRIES TO SPIN UP SOME SORT OF SFC LOW TO OUR SOUTH EARLY IN THE
PERIOD...YET THE GFS CONTINUES TO SUPRESS ANY LOW DEVELOPMENT.
TOWARDS THE VERY END OF THE PERIOD ON DAY 7...THE LONG RANGE
GUIDANCE SUGGESTS THAT ANOTHER CANADIAN SFC HIGH WILL BEGIN TO MOVE
INTO THE REGION FROM THE NW. AS FOR THE SENSIBLE FCST...WE CAN
EXPECT MOSTLY DIURNAL CHANCES FOR SCT CONVECTION EACH DAY/EVENING
WITH THE BEST CHANCES OVER THE SE ZONES. CHANCES INCREASE A BIT FOR
TUES AND WED OVER THE NW ZONES WITH BETTER LOW LVL CONVERGENCE
EXPECTED. TEMPS WILL START OUT RIGHT AROUND NORMAL AND REMAIN NEAR
NORMAL...IF NOT A FEW DEGREES ABOVE...THROUGH THE PERIOD.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THIS TAF CYCLE WITH
THE POSSIBLE EXCEPTION OF EARLY MORNING MVFR BR.  INITIALIZED TAF
WITH VCSH TO ACCOUNT FOR CURRENT SHRA COVERAGE WEST OF THE TERMINAL
ALONG WITH FEW LOW VFR CLOUDS.  EXPECTING IMPROVING CONDITIONS WITH
HEATING LOSS INTO MID EVENING THUS HIGH CLOUDS PREVAIL THROUGH MUCH
OF THE OVERNIGHT.  GUIDANCE FAVORS MVFR VISB WITH ANOTHER BOUT OF
LOW VFR STRATUS JUST BEFORE DAYBREAK AS THE MOIST PBL DECOUPLES.
VFR WILL RETURN AFTERWARD WITH A COLD FROPA BEING THE PRIMARY FOCUS
OF THE TAF ON THURSDAY.  KEPT WINDS SW UNDER DEVELOPING LOW VFR CU
CIGS THROUGH MIDDAY BEFORE VEERING FLOW NW AS THE FRONT INTRUDES
ALONG WITH TSRA MENTION IN THE FORM OF PROB30.

ELSEWHERE...VFR THROUGH THE FIRST FEW HOURS OF THE TAF CYCLE BEFORE
GUIDANCE FAVORS DETERIORATING VISB AT ALL SITES ASIDE FOR KAVL WHERE
BOTH VISB/CIGS WILL FALL.  AS THE BL DECOUPLES AROUND OR JUST AFTER
MIDNIGHT EXPECTING THE A FORE MENTIONED RESTRICTIONS TO
COMMENCE...THUS TAFS FEATURE MVFR VISB AT ALL SC SITES WITH TEMPOS
FOR IFR AT THE NC SITES THROUGH DAYBREAK.  AS WITH KCLT ABOVE...THE
PRIMARY FOCUS FOR THE TAF ON THURSDAY WILL BE THE PASSAGE OF A WEAK
COLD FRONT AND ANY CONVECTION IT INITIATES.  THEREFORE ALL SITES SEE
PROB30S FOR TSRA WITH TIMING ADJUSTMENTS ACCORDING TO LATEST CAM
GUID.  WINDS WILL INITIALIZE OUT OF THE SW BEFORE VEERING NW AT
AROUND 4-7KTS BY EARLY AFTERNOON AT ALL SITES.

OUTLOOK...HIGH PRESSURE WITH BUILD IN BEHIND A PASSING COLD FRONT
LATE ON THURSDAY ALLOWING FOR GENERALLY DRY AND QUIET WEATHER
THROUGH THE WEEKEND.  CHANCES FOR SHOWERS/THUNDERSTORMS AND THUS
RESTRICTIONS WILL RETURN FOR THE START OF THE NEW WORK WEEK.

CONFIDENCE TABLE...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       HIGH 100%     HIGH  83%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH  89%     HIGH 100%     HIGH 100%
KAVL       MED   77%     MED   61%     HIGH 100%     HIGH 100%
KHKY       HIGH  88%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH  89%     HIGH 100%     HIGH 100%
KAND       MED   77%     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...JPT
NEAR TERM...CDG/LG
SHORT TERM...JDL
LONG TERM...JPT
AVIATION...CDG



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