Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 281847
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
247 PM EDT FRI AUG 28 2015

.SYNOPSIS...
WEAK HIGH PRESSURE WILL LINGER OVER THE EAST WELL INTO THE WEEKEND
WITH MOISTURE GRADUALLY INCREASING FROM THE SOUTHWEST. TROPICAL
SYSTEM ERIKA WILL LIKELY BE SOMEWHERE IN THE VICINITY OF FLORIDA
MONDAY AND TUESDAY...WITH HIGH UNCERTAINTY ON HER LOCATION BY MID TO
LATE WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 235 PM EDT FRIDAY...SPLIT UPPER FLOW CONTINUES TO HIGHLIGHT
THE PATTERN ALOFT WITH A DEEPENING YET BROAD UPPER SOUTHERN STREAM
VORTEX OVER THE NORTHCENTRAL GULF...BROAD ANTICYCLONIC FLOW ATOP
THE DESERT SOUTHWEST...AND A SERIES OF WEAK WAVES PASSING OVER THE
OHIO VALLEY TO CENTRAL APPS REGION WITHIN THE NORTHERN STREAM.
AT THE SURFACE...HIGH PRESSURE OVER THE MID ATLANTIC CONTINUES
TO USHER DRIER AIR INTO THE NC/SC PIEDMONT AND FOOTHILLS REGION
AMONGST ENE FLOW.  LATEST SPC MESOANALYSIS DOES INDICATE SOME LOW
END INSTABILITY BUILDING OVER THE MTNS...WHICH IS REINFORCED BY
CURRENT VISB SAT ILLUSTRATION OF MODEST CU FIELD ATOP THE SAME
REGION.  NEAR TERM GUID CONTINUES TO FAVOR AT LEAST ISOLATED AND
PERHAPS A FEW SCATTERED SHOWERS AND THUNDERSTORMS THIS AFTERNOON
ALONG THE TN LINE WHERE BEST DIFFERENTIAL HEATING HAS OCCURRED.
THEREFORE KEPT MENTION OF SUCH IN THE FCST AND HWO.

OTHERWISE...RATHER CALM NIGHT AHEAD WITH MOSTLY CLEAR SKIES EARLY.
AFTERWARDS...THE ABOVE MENTIONED NORTHERN GULF DISTURBANCE WILL
ADVECT MOISTURE NORTHWARD ACROSS THE DEEP SOUTH INTO THE SOUTHERN
APPS REGION BY EARLY MID MORNING.  EXPECTING SKY COVER TO INCREASE
AHEAD OF SUCH IN THE FORM LOW STRATUS ACROSS MUCH OF NORTHEAST GA
AND THE EXTREME WESTERN CAROLINAS.  SKIES WILL BECOME GRADUALLY
CLEARER FURTHER NORTHEAST DUE TO PROXIMITY OF BOTH THE PRIMARY
MOISTURE SOURCE...AND THE PREVAILING SURFACE HIGH OVER THE MID
ATLANTIC.  BEYOND THAT...EXPECTING SAID LOW CLOUDS TO GIVE WAY
TO MID/HIGH CLOUDS BY MIDDAY WITH COVERAGE REMAINING AT ITS BEST
OVER THE WESTERN TIER OF THE FCST AREA.  A FEW GUID SOURCES DO
FAVOR SOME SHRA/TSRA ASSOCIATED WITH THE ENHANCED MOISTURE AXIS
INTRUSION SATURDAY AFTERNOON...HOWEVER SOUNDINGS INDICATE RATHER
POOR LAPSE RATES THUS OPTED TO KEEP ANY POP MENTION AT OR BELOW
SCATTERED LEVELS.  THESE MENTIONABLE POPS RESIDE GENERALLY ALONG
AND WEST OF THE INTERSTATE 26 CORRIDOR IN THE WESTERN CAROLINAS
AND ALL OF NORTHEAST GA.  TEMPERATURES THROUGH THE PERIOD WILL
REMAIN NEAR NORMAL LEVELS WITH THE BEST HEATING LIKELY TO OCCUR
OVER THE PIEDMONT REGIONS ON SATURDAY THANKS TO ENHANCED INSOLATION.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 230 PM FRIDAY...SHORT TERM BEGINS WITH LARGE NEBULOUS UPPER
TROUGH ACROSS THE DEEP SOUTH AND LOWER MISSISSIPPI VALLEY BEGINNING
TO SLOWLY PHASE WITH THE LONGWAVE TROUGH UP NEAR THE U.S./CANADA
BORDER. 300MB LOW IS A LITTLE BETTER DEFINED /AT 850MB THERE IS JUST
A WEAK REFLECTION IN THE WIND FIELD/ EVEN WITH A JET STREAK ROUNDING
THE SOUTHEAST BASE OF THE LOW. WEAK SYNOPTIC LIFT...ADDITIONAL DEEP
LAYER MOISTURE FROM THE EAST TO SOUTHEASTERLY FLOW OFF THE
ATLANTIC...AND WEAK UPSLOPE COMPONENT WILL SERVE TO INCREASE CLOUD
COVER SUNDAY. POPS INCREASE AS WELL. INSTABILITY WILL BE HIGHEST
ACROSS THE MOUNTAINS...GEORGIA...AND THE UPSTATE AS SURFACE HIGH
PRESSURE ACROSS NORTH CAROLINA WILL KEEP A NOSE OF STABILITY ACROSS
A GOOD PORTION OF THE PIEDMONT IN ALMOST A PSEUDO-WEDGE-LIKE
PATTERN. HIGH TEMPERATURES REFLECT THIS IDEA WITH HIGHS SUNDAY IN
THE LOWER TO MID 80S ACROSS THE UPSTATE AND NC PIEDMONT AND MOST OF
THE MOUNTAINS REMAINING IN THE MID 70S OR LOWER. LOWS SUNDAY
NIGHT WILL BE PRETTY CLOSE TO SEASONAL NORMALS.

THE UPPER LOW WILL CONTINUE TO BE ABSORBED BY THE LONGWAVE
PATTERN...GIVING WAY TO UPPER RIDGING BUILDING ACROSS THE CENTER OF
THE COUNTRY AS THE UPPER TROUGH PUSHES EAST. STILL ENOUGH MOISTURE
HANGING AROUND TO KEEP CHANCE POPS OVER THE MOUNTAINS AND EXTREME
SOUTHEAST ZONES ON MONDAY. FORECAST BECOMES MUCH MORE UNCERTAIN LATE
MONDAY AND BEYOND DEPENDING ON THE TRACK OF ERIKA. CURRENT GUIDANCE
DOES START LOFTING MOISTURE FROM THE SYSTEM ACROSS THE SOUTHEAST BY
LATE MONDAY...WITH ECMWF FARTHER NORTH THAN THE GFS BY TUESDAY 00Z.
CURRENT FORECAST HIGHS ON MONDAY CLOSE TO SEASONAL NORMALS BUT WILL
BE HIGHLY DEPENDING ON AMOUNT OF BOUNDARY LAYER MOISTURE.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 210 PM FRIDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON TUESDAY
WITH STEEP UPPER RIDGING OVER THE EASTERN CONUS AND AN EMBEDDED
CLOSED UPPER LOW JUST SOUTH OF THE GREAT LAKES. GO FORWARD...THE
EVOLUTION OF THE LOW REMAINS UNCLEAR. THE ECMWF MAINTAINS A MORE
ORGANIZED LOW THAT SLOWLY DRIFTS EASTWARD AND BY THE END OF THE
PERIOD HAS IT SOMEWHERE NEAR THE NEW ENGLAND COAST AND NEARLY
DISSIPATED. THE LATEST 12Z GFS...HOWEVER...IS MORE DIFFUSE WITH THE
SYSTEM RIGHT FROM THE START OF THE PERIOD AND PRETTY MUCH ABSORBS
IT BACK INTO THE MEAN UPPER FLOW BY THURS. OBVIOUSLY WHAT IS NOW TS
ERIKA WILL IMPACT THE UPPER LVL PATTERN EVOLUTION FOR MOST OF THE
PERIOD...SO I WOULD NOT PLACE TOO MUCH CONFIDENCE IN ANY PARTICULAR
MODEL SOLUTION AT THIS POINT. AT THE SFC..THE MAIN CONCERN FOR THE
PERIOD WILL BE THE TRACK AND IMPACTS ASSOCIATED WITH TS ERIKA. AS
THE PERIOD BEGINS LATE MON/EARLY TUES...ERIKA IS EXPECTED TO BE
SOMEWHERE OVER SOUTHERN FLORIDA WITH TROPICAL STORM FORCE WINDS. IT
THEN TURNS MORE NORTHWARD AND BY WED MORNING IS CENTERED NEAR THE
FL/GA BORDER. BEYOND THIS POINT THE GUIDANCE WEAKENS THE LOW AND
WASHES IT OUT OVER THE NEXT DAY OR 2. THE CMC MODEL MAINTAINS A MUCH
MORE SYMMETRICAL LOW ON WED AND THURS...BUT I DONT THINK THIS
SOLUTION IS VERY LIKELY. THERE ARE ALSO CONSIDERABLE DIFFERENCES
REGARDING HOW SOON THE DEEPER MOISTURE WILL MOVE INTO THE CWFA FROM
THE SOUTH. THE ECMWF HAS DEEPER MOISTURE OVER MOST OF THE FCST AREA
BY THE START OF THE PERIOD AND THEN MOVES IT SE OF THE AREA BY THURS
MORNING WHILE THE GFS DOES NOT MOISTEN THINGS UP UNTIL LATE
WED/EARLY THURS AND KEEPS THE DEEP MOISTURE OVER THE CAROLINAS THRU
DAY 7. REGARDLESS...WE CAN EXPECT A STEADY INCREASE IN MOIST SLY
FLOW DURING THE FIRST HALF OF THE PERIOD WITH SOME DRYING POSSIBLE
ON THURS AND FRI...BUT CERTAINLY NOT GUARANTEED. AT PRESENT...DAYS
4-7 QPF AMOUNTS DO NOT LOOK VERY IMPRESSIVE...BUT THINGS COULD
CERTAINLY TREND WETTER OVER THE NEXT FEW DAYS AND FLOODING COULD BE
MORE OF A CONCERN.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...VFR THROUGH THE PERIOD.  HIGH PRESSURE TO THE NORTH
WILL ALLOW DRIER CONDITIONS TO PERSIST DURING THIS TAF CYCLE.
INITIALIZED TAF WITH ENE WINDS WITH SOME ESE FLOW POSSIBLE THEREBY
SETTING UP CROSSWIND ISSUES AROUND THE 22Z-02Z TIMEFRAME THIS
AFTERNOON/EVENING.  OTHERWISE...HIGH LEVEL CIRRUS WILL PREVAIL
THROUGH THE OVERNIGHT BEFORE LLV MOISTURE ADVECTS IN FROM THE
SOUTH THUS POSSIBLY YIELDING A SCT/BKN STRATUS DECK AT 020-030.
HELD OFF ON ANY MVFR CIGS WITH A FORE MENTIONED STRATUS AS SOME
GUIDANCE HAS TRENDED A TAD DRIER.  EXPECTING ANY LOW STRATUS TO
PERSIST THROUGH DAYBREAK INTO MID/LATE MORNING BEFORE BL HEATING
ERODES SUCH GIVING WAY TO HIGH LEVEL CIRRUS ATOP LIGHT ENE FLOW.

ELSEWHERE...VERY SIMILAR TO THAT OF KCLT ABOVE HOWEVER WITH
BETTER CHANCES FOR MVFR RESTRICTIONS AT SITES FURTHER WEST WHERE
DEEPER LLV MOISTURE PLUME IS EXPECTED TO ADVECT IN BY MORNING.
THUS...INITIALIZED ALL TAFS VFR AT SCT 040-050 BEFORE IMPROVING TO
HIGH LEVEL CIRRUS AT 25K BY EARLY EVENING.  MODELS DO CONTINUE TO
HINT AT SOME FOG ISSUES IN AND AROUND THE MTN VALLEYS BY SATURDAY
MORNING...THUS DID INCLUDE...HOWEVER KEPT AT MVFR LEVELS FOR KAVL.
WINDS THROUGH THE PERIOD WILL REMAIN SE AT KAVL AND ENE/ESE FOR ALL
SC SITES AT AROUND 6-10KTS THIS AFTERNOON BEFORE CALMING TONIGHT.

OUTLOOK...CHANCES FOR DIURNALLY FAVORED SHOWERS AND THUNDERSTORMS
WILL CONTINUE TO INCREASE AS MOISTURE ADVECTS IN FROM THE SOUTHEAST
THROUGH THE WEEKEND YIELDING POSSIBLE RESTRICTIONS.  EARLY MORNING
STRATUS/FOG RESTRICTIONS COULD ALSO OCCUR FOR AREAS THAT RECEIVED
PREVIOUS RAINFALL LEADING TO ENHANCED MOISTURE IN THE BL.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  93%     HIGH  94%
KGSP       HIGH 100%     HIGH 100%     MED   79%     MED   77%
KAVL       HIGH 100%     HIGH 100%     MED   77%     HIGH  87%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  80%
KGMU       HIGH 100%     HIGH 100%     MED   79%     MED   77%
KAND       HIGH 100%     HIGH 100%     MED   75%     MED   79%

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
SHORT TERM...TDP
LONG TERM...JPT
AVIATION...CDG


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