Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 272313
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
713 PM EDT THU AUG 27 2015

.SYNOPSIS...
CANADIAN HIGH PRESSURE WILL MOVE OFF THE MID-ATLANTIC COAST THROUGH
THE END OF THE WORK WEEK. THIS WILL RESULT IN INCREASING MOISTURE
AND CHANCES FOR SCATTERED SHOWERS AND THUNDERSTORMS OVER THE WEEKEND
INTO EARLY NEXT WEEK. TROPICAL CYCLONE ERIKA IS EXPECTED TO APPROACH
SOUTHERN FLORIDA BY EARLY SUNDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
2315 UTC UPDATE...WINDS HAVE BEEN UPDATED WITH A BLEND OF THE LATEST
NAM AND ADJMAV. SKY COVER HAD BEEN UPDATED FROM VISIBLE SATELLITE
IMAGERY. AREAS OF DAYBREAK FOG IN THE MOUNTAINS WERE ADJUSTED BASED
ON THE LATEST MODEL DATA.

2015 UTC UPDATE...SKY COVER WAS UPDATED PER THE LATEST VISIBLE
SATELLITE IMAGERY...RESULTING IN A SLIGHT DECREASE ACROSS MUCH OF
THE AREA.

AS OF 230 PM EDT THURSDAY...NEARLY FULL LATITUDE DECOUPLING
UPPER TROF RESIDES OVER THE EASTERN CONUS WHILE ANTICYCLONIC
FLOW PREVAILS AROUND AN UPPER HIGH OVER THE DESERT SOUTHWEST.
AT THE SURFACE...A NEARLY STATIONARY COLD FRONTAL AXIS OFF THE
CAROLINA COASTLINE CONTINUES TO PROVIDE A FOCUS FOR CONVECTION OVER
THAT REGION.  CLOSER TO HOME...LATEST SPC MESOANALYSIS INDICATES
MINOR DESTABILIZATION ACROSS PORTIONS OF WESTERN NC AND ALL OF
NORTHEAST GA AND THE SC UPSTATE...WHICH CONTINUES TO PROMOTE LOW
CU DEVELOPMENT.  AS THE UPPER PATTERN DECOUPLES...ANY NORTHERN
STREAM SHORTWAVE ENERGY WILL SLIDE ACROSS THE SOUTHERN/CENTRAL
APPS LATER THIS AFTERNOON INTO EARLY EVENING.  MODELS CONTINUE TO
INDICATE SOME CONVECTION ALONG THE MTN RIDGETOPS...POSSIBLY AIDED
BY VEERED EASTERLY UPSLOPING...THEREFORE CONTINUED WITH LOW END
SLIGHT CHANCE POPS INTO EARLY EVENING BEFORE ALL POPS ARE REMOVED
CLOSER TO MIDNIGHT.

SURFACE HIGH PRESSURE WILL ADVECT ACROSS THE APPS THROUGH THE
OVERNIGHT WHILE THE SOUTHERN STREAM UPPER WAVE RETROGRADES SLIGHTLY
TO THE WEST OVER THE NORTHCENTRAL GULF.  MODELS INDICATE EASTERLY
VEERED SFC-H85 FLOW THROUGH FRIDAY MORNING LEADING TO WEAK UPGLIDE
POTENTIAL ATOP THE INTRUDING SUMMERTIME WEDGE LIKE SFC PRESSURE
PATTERN THANKS TO HIGH PRESSURE OFF TO THE IMMEDIATE NORTHEAST.
AS A RESULT...PARTLY/MOSTLY CLOUDY SKIES ARE EXPECTED FRIDAY
MORNING...ESPECIALLY ACROSS THE EASTERN TIER OF THE FCST AREA.
SAID SKY COVER WILL EVENTUALLY SCT INTO THE LATE MORNING TO EARLY
AFTERNOON AS THE BOUNDARY LAYER HEATS YIELDING A FEW CUMULUS THROUGH
THE PERIOD.  AS FOR PRECIPITATION...MODELS ARE FAIRLY CONSERVATIVE
WITH REGARDS TO DESTABILIZATION WITH THE BEST OF WHICH RESIDING
ONCE AGAIN ALONG THE HIGH TERRAIN WHERE DIFFERENTIAL HEATING WILL
BE MAXIMIZED...THUS THE FCST FEATURES SLIGHT CHANCE POPS FOR SUCH.
TEMPERATURES ON FRIDAY WILL REMAIN A FEW DEGREES BELOW NORMAL.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 230 PM THURSDAY...SHORT TERM BEGINS WITH LONGWAVE UPPER TROUGH
LIFTING INTO CANADA...WITH UPPER WEAKNESS/ENERGY OVER THE SOUTHEAST
AND LOWER MISSISSIPPI VALLEY BREAKING OFF. A WEAK SURFACE LOW
DEVELOPING OFF THE CAROLINA COAST WILL BEGIN TO LIFT NORTHEAST...AND
WITH SURFACE HIGH IN PLACE OVER THE MID-ATLANTIC STATES THE
SOUTHEASTERLY FLOW WILL BEGIN TO BRING MORE MOISTURE INTO THE REGION
FOR THE SHORT TERM. THE UPPER WEAKNESS OVER THE SOUTHEAST WILL BEGIN
TO PHASE WITH ANOTHER SHORTWAVE CROSSING THE GREAT LAKES SATURDAY
INTO SUNDAY...THE LATTER HELPING TO PULL THE FORMER BACK TO THE
NORTHEAST. AS IT DOES SO...AN ASSOCIATED VORT MAX AND EVEN A WEAK
UPPER JET WILL PUSH ACROSS THE CAROLINAS. AS A RESULT...EXPECT
CLOUDS TO BE ON THE INCREASE ESPECIALLY ON SATURDAY...AS POPS SPREAD
ACROSS THE AREA FROM THE SOUTH AND SOUTHWEST AS WELL...WITH SOME
LIKELIES SHOWING UP ACROSS THE MOUNTAINS AND FOOTHILLS BY SUNDAY
AFTERNOON. WITH INCREASED CLOUDS AND CHANCE OF PRECIPITATION...
EXPECT HIGHS TO CONTINUE TO HOVER JUST BELOW SEASONAL NORMALS BUT
WITH LOWS INCREASING TO ABOVE NORMAL VALUES AS A RESULT OF THE
ADDITIONAL SURFACE MOISTURE. DEFINITELY SOME DIFFERENCES IN
AVAILABLE INSTABILITY BETWEEN THE GFS AND NAM BUT INSTABILITY WILL
INCREASE FROM THE SOUTHWEST SATURDAY...WITH THUNDER POSSIBLE PRETTY
MUCH ACROSS THE ENTIRE AREA ON SUNDAY.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 245 PM THURSDAY...MEDIUM RANGE/EXTENDED HAS A LOT OF
UNCERTAINTY ESPECIALLY THE FARTHER OUT WE GO IN THE FORECAST. TO
START WITH...THE UPPER WEAKNESS FROM THE SHORT TERM WILL SLOWLY
DISSIPATE AS IT PHASES WITH AND IS ABSORBED BY THE LONGWAVE TROUGH
WITH THE WAVETRAIN UP ALONG THE U.S./CANADA BORDER. THIS GIVES WAY
TO UPPER RIDGING BY TUESDAY. THE PATTERN SUPPORTS A SLIGHT
INCREASING TREND IN TEMPERATURES...BUT THE UNKNOWNS START PILING UP
QUICKLY DEPENDING ON WHAT ERIKA DECIDES TO DO. CURRENT OFFICIAL
FORECAST HAS THE STORM HUGGING THE EAST SIDE OF THE FLORIDA
PENINSULA AS A HURRICANE THROUGH TUESDAY MORNING. 12Z GUIDANCE /BOTH
GFS AND ECMWF/ KEEP IT RIGHT ALONG THE SOUTH CAROLINA COAST...AND
THEN PUSH IT EAST AND OUT TO SEA AS THE UPPER RIDGE PUSHES EAST.
THIS COULD VERY LIKELY LEAVE OUR AREA MOSTLY DRY. FOR NOW THOUGH
HAVE TAKEN A SPLIT POP PARADIGM WITH CHANCE POPS IN SOUTHEAST
ZONES...IN CLOSER PROXIMITY TO THE INFLUENCE OF ERIKA...AND CHANCE
POPS IN THE MOUNTAINS...AS NORTHWEST FLOW INCREASES AND WOULD LEND
THE UPSLOPE COMPONENT TO THE AREA DESPITE SYNOPTIC SUBSIDENCE AROUND
THE PERIPHERY OF THE STORM...WITH SLIGHT CHANCE BETWEEN. WITHOUT
DIFFERENT GUIDANCE...HAVE KEPT TREND OF HIGHS AT OR JUST SLIGHTLY
BELOW SEASONAL NORMALS AND LOWS AT OR JUST SLIGHTLY ABOVE. OBVIOUSLY
HIGHLY DEPENDENT ON BOUNDARY LAYER MOISTURE. HOWEVER...OF COURSE ANY
SHIFT IN THE TRACK WILL HAVE VARYING IMPACTS ON THE FORECAST FOR
NEXT WEEK SO STAY TUNED.

&&

.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
AT KCLT...VFR. GUIDANCE HAD VARIED ON CLOUD HEIGHTS OVER THE
FIELD...WITH A TENDENCY TOWARD HIGH CLOUDS AROUND DAYBREAK. LOW VFR
CLOUDS ARE SUPPORTED JUST TO THE WEST HOWEVER...WHICH COULD YIELD
LOW VFR CIGS. GUIDANCE DOES NOT SUPPORT DAYBREAK FOG. LIGHT WINDS
WILL FAVOR THE ENE.

ELSEWHERE...OTHER THAN DAYBREAK MVFR AT KAVL...A GUIDANCE BLEND
SUPPORTS VFR CONDITIONS. MODELS INCONSISTENCY LEADS TO LIMITED
CONFIDENCE HOWEVER. SOME LOW VFR CIGS ARE POSSIBLE...STARTING
OVERNIGHT IN THE MOUNTAINS...AND SPREADING TO THE FOOTHILLS BY DAWN.
IMPROVEMENT IS EXPECTED BY MIDDAY. WINDS WILL FAVOR THE NE IN THE
FOOTHILLS...AND WILL CHANGE FROM LIGHT AND VARIABLE AT KAVL TO SE
AFTER DAWN.

OUTLOOK...MOISTURE WILL SLOWLY INCREASE FROM THE SOUTH AND EAST
THROUGH THE WEEKEND AND THEREFORE ISOLATED TO SCATTERED AFTERNOON
AND EVENING SHRA/TSRA CHANCES WILL INCREASE.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  91%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     LOW   41%     HIGH 100%
KHKY       HIGH 100%     HIGH  83%     HIGH  83%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH  94%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     MED   71%     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

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...CDG/JAT
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...JAT


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