Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 170620
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
220 AM EDT WED SEP 17 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA TODAY...ENHANCING CHANCES FOR
SHOWERS AND THUNDERSTORMS THROUGH TONIGHT. IN ITS WAKE...SEASONABLY
COOL AIR WILL SPILL INTO THE REGION WEDNESDAY. THE COOL CONDITIONS
AND MOSTLY DRY WEATHER WILL LAST INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 205 AM...CONVECTION IS FINALLY SHOVING OUT OF THE SOUTHEAST
TIER OF FORECAST ZONES EARLY THIS MORNING. THE BACKDOOR FRONT
CURRENTLY EXTENDS ROUGHLY ALONG THE I-85 CORRIDOR...AND CANNOT RULE
OUT AN ADDITIONAL SHOWER OR PERHAPS A STORM DEVELOPING IN THIS
GENERAL AREA OVERNIGHT...BUT FEEL THE PROBABILITY SHOULD BE 20
PERCENT AT BEST. OTHERWISE...THE DRIER/COOLER AIR WILL FILTER IN AT
A SNAILS PACE THIS MORNING...WITH PATCHY FOG/LOW STRATUS LIKELY IN
THE VERY MOIST ENVIRONS.

1000 PM ED UPDATE...THE COMBINATION OF +1000J/KG MUCAPE AND LLVL
CONVERGENCE IN THE VICINITY OF THE SURFACE BOUNDARY OVER THE
CHARLOTTE METRO AREA AND UNION NC WAS KEEPING THE CONVECTION
ONGOING. LATEST RADAR TREND SHOWS THE AXIS OF THE HEAVIEST RAIN IS
SLOWLY SHIFTING SOUTH. THEREFORE...HAVE INCREASED POPS FOR THE
AFFECTING AREAS THRU MIDNIGHT. OTHERWISE...THE FRONT SHOULD CONTINUE
TO PUSH SOUTH OVERNIGHT SETTING UP A COOL AIR WEDGE OVER THE
FORECAST AREA. THIS WILL YIELD A RATHER QUIET CONDITIONS OVERNIGHT
WITH PREVAILING NE WINDS AND CONSIDERABLE LLVL CLOUDINESS.

745 PM EDT UPDATE...SCATTERED CONVECTION WILL CONTINUE TO AFFECT
PARTS OF THE WESTERN NC PIEDMONT AND SOUTHERN UPSTATE SC OVER THE
NEXT SEVERAL HOURS. LATEST CONVECTION ALLOWING MODELS SUGGEST THAT
THE CONVECTION SHOULD DIMINISH AFTER MIDNIGHT...SO POPS WERE UPDATED
TO RAMP DOWN ACCORDINGLY. OTHERWISE...EXPECT A COOL AIR WEDGE TO SET
UP ACROSS THE FORECAST AREA OVERNIGHT...LEADING TO CONSIDERABLE LOW
CLOUDS WITH PATCHY FOG. HENCE...HAVE INCREASED THE SKY COVER AND
MENTIONED PATCHY FOG FOR MOST LOCATIONS THRU SUNRISE.

AS OF 450 PM EDT TUESDAY...CONVECTION CONTINUES TO EXPAND THIS
AFTERNOON ACROSS THE REGION AMONGST A MODERATELY UNSTABLE AIR MASS.
LATEST SPC MESOANALYSIS INDICATES UPWARDS OF 2000J/KG SBCAPE PRESENT
ALONG THE I85 CORRIDOR WITH A DISTINCT MAXIMA ACROSS PORTIONS OF THE
SC UPSTATE. THE ENVIRONMENT WILL REMAIN FAVORABLE FOR DAMAGING WINDS
AND POTENTIALLY SEVERE HAIL THROUGH THE AFTERNOON. CURRENT FORECAST
REMAINS ON TRACK THEREFORE NO CHANGES WERE MADE.

PREVIOUS DISCUSSION...

AS OF 240 PM EDT TUESDAY...LATEST SPC MESOANALYSIS INDICATES A
RATHER LARGE AND INCREASINGLY UNSTABLE AIRMASS ACROSS MUCH OF THE
LOWER TERRAIN OF NORTHEAST GA AND THE WESTERN CAROLINAS.  CONVECTION
INITIATING ACROSS THE FOOTHILLS OF THE BLUE RIDGE INTO THE NC
PIEDMONT WILL CONTINUE THROUGH THE AFTERNOON WITH COVERAGE EXPANDING
SOUTHWARD INTO THE UPSTATE OF SC AND NORTHEAST GA.  SOUNDINGS ACROSS
THESE ZONES DO INDICATE DECENT CAPE THROUGH THE LOWEST 400MB WITH
INCREASING SHEAR AHEAD OF AN APPROACHING WEAK UPPER SHORT WAVE.
THUS...AFTERNOON FORECAST FEATURES ISOLATED/SCATTERED POPS WITH A
FEW STRONG THUNDERSTORMS POSSIBLE WITH GUSTY WINDS AND CLOUD TO
GROUND LIGHTNING BEING THE PRIMARY THREATS.  OTHERWISE...ASIDE FOR
POSSIBLE/BRIEF REDEVELOPMENT ALONG BACK DOOR FRONTAL
BOUNDARY...EXPECTING CONVECTION TO ERODE BY LATE EVENING AS HEATING
SUBSIDES AND DRY AIR ADVECTS IN.  GUIDANCE DOES INDICATE THAT THE
BOUNDARY ITSELF WILL BE RATHER SLOW TO PUSH THROUGH THE PIEDMONT
REGIONS OF NC/SC OVERNIGHT LEADING TO CONTINUED CLOUDINESS AND LOW
END PRECIPITATION CHANCES INTO MORNING ALONG AND EAST OF I77.

FOR WEDNESDAY...HIGH PRESSURE SLIDING EAST THROUGH THE OHIO VALLEY
WILL CONTINUE TO DOMINATE THE WEATHER PATTERN LEADING TO PREVAILING
NORTHERLY FLOW AND WELL BELOW NORMAL TEMPERATURES AMIDST MOSTLY
SUNNY SKIES.  FORECAST WILL REMAIN DRY FOR MOST OF THE REGION WITH
ONLY ISOLATED SHOWERS POSSIBLE ACROSS THE EAST WHERE LINGERING
FRONTAL MOISTURE RESIDES...AND ALSO ALONG PORTIONS OF THE WESTERN NC
MOUNTAINS WHERE UPSLOPE FLOW COULD INDUCE A FEW SHOWERS.  NOT
EXPECTING ANY DEEP CONVECTION ON TUESDAY AS DRIER/COOLER BOUNDARY
LAYER WILL INHIBIT INSTABILITY THROUGHOUT THE DAY.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
AS OF 245 PM TUE...LONG WAVE TROF REMAINS OVER THE ERN CONUS THRU
THE PERIOD...ALTHOUGH THE AXIS DOES MOVE OFF SHORE BY THE END OF THE
PERIOD. A SERIES OF WEAK SHORT WAVES MOVE ACROSS THE AREA THRU THE
TROF. HOWEVER...THERE IS LITTLE DEEP MOISTURE AND FORCING ASSOCIATED
WITH THESE SYSTEMS. THERE IS QUITE A BIT OF LOW LEVEL MOISTURE AND
SOME MECHANICAL FORCING IN THE LOW LEVEL ELY FLOW WITH SFC HIGH
PRESSURE REMAINING RIDGED INTO THE AREA FROM THE NORTH.
HOWEVER...FORECAST SOUNDINGS SHOW THE ATMOS REMAINS CAPPED THRU THE
PERIOD WITH WARM MID LEVEL TEMPS. THEREFORE...HAVE GONE WITH A DRY
FORECAST THRU THE PERIOD...EXCEPT FOR SOME LINGERING CONVECTION WED
EVENING. THERE SHUD BE QUITE A BIT OF NIGHT TIME CLOUDS WITH THE LOW
LEVEL MOISTURE AND ELY FLOW...WITH SOME CLEARING DURING THE DAY.
TEMPS WILL BE AROUND 5 DEGREES BELOW NORMAL.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 300 PM TUE...UPPER TROF BRIEFLY BUILDS INTO THE AREA EARLY IN
THE MEDIUM RANGE AS AN UPPER TROF MOVES OFF SHORE. ANOTHER UPPER
TROF BUILDS OVER THE ERN CONUS ON MON AND REMAINS ON TUE. AT THE
SFC...HIGH PRESSURE REMAINS RIDGED INTO THE AREA FROM THE NORTH WITH
A MODERATING AIR MASS UNTIL A COLD FRONT CROSSES THE AREA MONDAY.
HIGH PRESSURE BEGINS TO BUILD IN AS THE FRONT SLOWLY MOVES EAST ON
TUE. EXPECT A DRY FCST FRI AND SAT...WITH ONLY A SLIGHT CHC OF
PRECIP MOVING IN ACROSS THE WEST AHEAD OF THE FRONT ON SUN. MTNS
WILL SEE THE BEST CHC OF PRECIP MON WHERE MOISTURE AND FORCING ARE
HIGHEST. PRECIP CHC DIMINISHES TO SLIGHT CHC FOR TUE AND MAINLY
OUTSIDE OF THE MTNS IN THE LINGERING MOISTURE BEHIND THE SLOW MOVING
FRONT. BELOW NORMAL TEMPS RISE TO A LITTLE ABOVE NORMAL AHEAD OF THE
FRONT...THEN DROP A LITTLE BELOW NORMAL BEHIND THE FRONT ON TUE.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...ANOTHER LOW CONFIDENCE FORECAST THIS PERIOD...AS A NUMBER
OF COMPETING FACTORS WILL DETERMINE THE SIGNIFICANCE OF FLT
RESTRICTIONS LATER THIS MORNING. A LIFR CIG RECENTLY DEVELOPED...
LIKELY AS A RESULT OF A WET GROUND DUE TO HEAVY RAIN THAT FELL
AROUND THE TERMINAL EARLIER. HOWEVER...THIS IS NOT ANTICIPATED TO
STICK AROUND...AS INCREASING (ALBEIT LIGHT) NE WINDS SHOULD BEGIN TO
BRING SLIGHTLY DRIER AIR INTO THE AREA. NEVERTHELESS...WITH THE WET
GROUND AND PLENTY OF LINGERING MOISTURE...EXPECT LMVFR CIGS TO
DEVELOP BY DAYBREAK. CERTAINLY CANNOT RULE OUT IFR CONDITIONS
REDEVELOPING...BUT JUST DON/T HAVE THE CONFIDENCE TO FORECAST THESE
CONDITIONS ATTM. ONCE THE MVFR CIGS DEVELOP...THEY SHOULD BE SLOW TO
LIFT LATER TODAY...AND ARE  ACTUALLY EXPECTED TO REMAIN THROUGH THE
PERIOD. SHOWER REDEVELOPMENT MAY OCCUR IN THE VCNY OF THE TERMINAL
DURING THE AFTERNOON... ALTHOUGH COVERAGE SHOULD REMAIN ISOLATED AND
A TAF MENTION IS NOT WARRANTED ATTM. OTHERWISE...LIGHT NE WINDS
SHOULD DEVELOP OVER THE NEXT COUPLE OF HOURS...AND PERSIST THROUGH
THE PERIOD.

ELSEWHERE...MADE SOMEWHAT RADICAL CHANGES TO THE KAVL TAF...AS A
PERSISTENT UP-VALLEY WIND...AND DEVELOPMENT OF MVFR STRATOCU IS
RESULTING IN A TEMP/DEWP SPREAD THAT IS MAKING DEVELOPMENT OF
SUB-MVFR CONDITIONS LESS LIKELY...AND THIS IS SOMEWHAT SUPPORTED BY
THE LATEST SHORT TERM GUIDANCE. HOWEVER...SUSPECT THAT WINDS WILL
EVENTUALLY DIMINISH...AND IFR CONDITIONS COULD STILL VERY WELL
DEVELOP BY DAYBREAK...SO A TEMPO FOR 2SM/BKN004 WAS INCLUDED AFTER
10Z. OTHERWISE...THE FORECASTS FOR KGSP/KHKY ARE QUITE PROBLEMATIC
AND LOW CONFIDENCE...AS LIGHT NE WINDS AND VFR STRATOCU HAVE BECOME
ESTABLISHED (WHICH WOULD ARGUE AGAINST LOW STRATUS/FOG
DEVELOPMENT)...BUT ON THE OTHER HAND THE SOIL IS VERY WET (ESP NEAR
KGSP) AND LOW LEVEL MOISTURE REMAINS PLENTIFUL. NEVERTHELESS...WILL
COUNT ON THE DEEP NE FLOW EVIDENT ON LATEST RADAR WIND PROFILE
DISPLAY AND AFOREMENTIONED FACTORS KEEPING CONDITIONS AT LMVFR OR
BETTER LATER THIS MORNING. MEANWHILE...AM A LITTLE MORE CONFIDENT
THAT CONDITIONS SHOULD BE NO WORSE THAN MVFR AT KAND/KGMU. CIGS
SHOULD PERSIST IN THE VFR/MVFR RANGE THROUGH MUCH OF THE DAY...
ALTHOUGH CLOUDS MAY SCATTER AT KAND AS SOME DRIER AIR ARRIVED FROM
THE WEST.

OUTLOOK...ALTHOUGH THE CHANCES FOR DIURNAL CONVECTION WILL GREATLY
DIMINISH AFTER WEDNESDAY...THE POTENTIAL FOR LATE NIGHT/MORNING
FOG/STRATUS WILL PERSIST INTO LATE WEEK...ESP IN THE MTN VALLEYS.
CONDITIONS MAY FINALLY DRY OUT FOR THE WEEKEND.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  87%     HIGH  88%     MED   76%     MED   77%
KGSP       HIGH  92%     MED   75%     HIGH  89%     HIGH  95%
KAVL       MED   64%     MED   72%     HIGH  83%     MED   71%
KHKY       MED   74%     MED   75%     MED   73%     MED   67%
KGMU       HIGH  94%     MED   73%     HIGH  89%     HIGH  95%
KAND       HIGH 100%     HIGH  91%     HIGH  93%     HIGH  86%

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





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