Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 161758
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
ISSUED BY NATIONAL WEATHER SERVICE COLUMBIA SC
158 PM EDT TUE SEP 16 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 TONIGHT/...
AS OF 150 PM EDT TUESDAY...DESPITE INCREASINGLY UNSTABLE
ENVIRONMENT AND ENCROACHING BACK DOOR FRONTAL BOUNDARY...NORTHEAST
GA AND THE WESTERN CAROLINAS REMAIN CONVECTION FREE. SATELLITE
IMAGERY DOES INDICATE EXPANDING CU FIELD ACROSS THE LOWER TERRAIN
WHERE DOWNSLOPING FLOW HAS ALLOWED FOR ABUNDANT
HEATING/DESTABILIZATION. STILL EXPECTING CONVECTION TO INITIATE
WITHIN THE NEXT FEW HOURS ALONG THE BLUE RIDGE SOUTHWARD INTO
NORTHEAST GA AND THE PIEDMONT REGIONS OF THE CAROLINAS.
THUS...OPTED FOR NO CHANGES TO THE FORECAST WITH THIS UPDATE. FULL
FORECAST DISCUSSION TO FOLLOW WITHIN THE HOUR.

PREVIOUS DISCUSSION...

AS OF 845 AM...VERY SPOTTY SHOWERS CONTINUE ACROSS THE REGION...WITH
SLIGHTLY BETTER COVERAGE NOW DEVELOPING CLOSER TO THE FRONT OVER
EXTREME NW NC. WILL MAINTAIN MAINLY ISOLATED LATE MORNING POPS AND
RAMP UP TO MORE SOLID SCATTERED COVERAGE WITH THE FRONT THIS
AFTERNOON. HAVE ALSO TRIMMED MAXES A DEGREE OR SO IN MOST AREAS IN
LINE WITH THE 06Z BIAS CORRECTED MOS AND IN LIGHT OF PREVIOUS DAYS.
OTHERWISE...THE FOG AND LOW STRATUS SHOULD IMPROVE RAPIDLY GIVEN
THE LIGHT DOWNSLOPE FLOW.

A SERIES OF SUBTLE SHORT WAVES IS EXPECTED TO RIPPLE THROUGH THE
DEVELOPING EASTERN TROUGH OVER THE NEXT 24 HOURS...WITH A MODEL
CONSENSUS SUGGESTING THE FIRST ONE WILL APPROACH OUR AREA BY EARLY
THIS EVENING...ALONG WITH AN ACCOMPANYING COLD FRONT. THESE FEATURES
WILL FIND AN AIR MASS WITH LESS DEEP-LAYER MOISTURE CONTENT THAN
WE/VE BEEN SEEING IN RECENT DAYS. HOWEVER...THE ADDITIONAL HEATING
(WITH MAXES EXPECTED TO PEAK NEAR CLIMO) WILL RESULT IN MODERATE
DESTABILIZATION ACROSS THE REGION THIS AFTERNOON. THUS...EXPECT SCT
CONVECTION TO DEVELOP ACROSS THE MTNS BY LATE AFTERNOON...WITH
ACTIVITY TRUCKING EASTWARD FAIRLY QUICKLY IN MODERATELY FAST W/NW
FLOW. SPEAKING OF WHICH...DEEP LAYER SHEAR IS EXPECTED TO BE RATHER
RESPECTABLE TODAY...WITH FORECAST SOUNDINGS DEPICTING BULK 0-6KM
SHEAR OF AROUND 30 KTS. HOWEVER...INSTABILITY IS NOT EXPECTED TO BE
VERY ROBUST (SBCAPE 1500-2000 J/KG)...BUT SOME DEGREE OF MESOSCALE
ORGANIZATION AND A BRIEF SEVERE WIND GUST OR TWO CANNOT BE RULED
OUT.

CONVECTIVE CHANCES WILL LIKELY REACH A NADIR DURING EARLY EVENING...
THEN GRADUALLY DIMINISH TOWARD THE OVERNIGHT HOURS. WITH PLENTY OF
LOW LEVEL JUICE LINGERING...MIN TEMPS SHOULD AVERAGE A LITTLE ABOVE
CLIMO FOR ONE MORE NIGHT BEFORE THE COOLER AIR ARRIVES.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUE...AN AMPLIFIED UPPER PATTERN WILL BE SEEN OVER THE
CONUS DURING THE PERIOD...KEEPING MOST OF THE ERN STATES UNDER A
LONGWAVE TROUGH. HOWEVER THE PATTERN DOES KEEP MOVING AS THE RIDGE
MOVES FROM THE INTERMOUNTAIN WEST INTO THE PLAINS...WITH A WEAK SFC
HIGH BUILDING INTO THE ERN CONUS DOWNSTREAM OF IT. OUR AREA WILL BE
UNDER THE INFLUENCE OF THE WEAK HIGH WEDNESDAY BEFORE A LARGER
CANADIAN HIGH SLIDES IN FOR THURSDAY. A COUPLE OF WEAK SHORTWAVES
BURIED IN THE UPPER FLOW ARE ALSO SHOWN ON THE NAM/GFS/EC...RESOLVED
MORE DISTINCTLY ON THE NAM ON ACCOUNT OF ITS HIGHER RESOLUTION.
MOISTURE PROFILES APPEAR INSUFFICIENT FOR THESE WAVES TO PRODUCE ANY
PRECIP ON THEIR OWN...AND THEY ARE POORLY TIMED TO ENHANCE DIURNAL
CONVECTION WITHIN THE CWFA. IN FACT ON THU THE SUBSIDENCE IN THE WAKE
OF A WAVE APPEARS TO BE ITS BIGGEST IMPACT. THOUGH LAPSE RATES ARE
NOT THAT BAD EITHER DAY...MODELS SUPPORT SCHC POPS ACRS MUCH OF THE
AREA WED. THE GREATER SUBSIDENCE THU LENDS CONFIDENCE TO A DRY FCST.
TEMPS WILL BE A COUPLE CATEGORIES BELOW CLIMO BOTH DAYS THOUGH
CLEARER SKIES THU WARRANT SLIGHTLY WARMER MAXES. THE SFC HIGH AND
TIGHTENING HEIGHT GRADIENT WITHIN THE DOWNSTREAM UPPER TROUGH LINE UP
THU NIGHT TO ALLOW CAD TO FORM WHICH PERSISTS INTO THE WEEKEND.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 200 AM TUE...AS UPPER TROUGH PROGRESSES EWD THRU THE CANADIAN
MARITIMES...EARNEST COLD AIR DAMMING CONTINUES OVER OUR REGION
REINFORCING SEASONABLY COOL TEMPS FRI-SAT. EASTERLY FLOW MAY PRODUCE
SOME CLOUD COVER BUT PRECIP IS NOT EXPECTED. PARENT HIGH MOVES
OFFSHORE FAIRLY QUICKLY BUT THE WEDGE HOLDS ON THRU SATURDAY.
FALLING UPPER HEIGHTS TAKE THEIR TOLL ON IT BY SUNDAY
MORNING...BRINGING RETURN FLOW AHEAD OF A LOW PRESSURE SYSTEM
CROSSING THE GREAT LAKES.  16/00Z GFS AND 15/12Z EC CONTINUE TO
DEPICT THIS SYSTEM DIFFERENTLY BUT BOTH FEATURE A COLD FRONT MOVING
OUT OF THE TENN VALLEY AND INTO OUR AREA EARLY IN THE WEEK. EACH
MODEL AGREES WITH THE PATTERN SEEN ON THEIR OWN PREVIOUS RUNS.
BEYOND THAT THE GENERAL CONSENSUS IS FOR AN AMPLIFYING UPPER
PATTERN...WITH A DEEP ERN CONUS TROUGH CARVING OUT BY NEXT TUESDAY.
TEMPS TREND UPWARD THRU THE PERIOD AS THE WEDGE GIVES WAY AND THE
FROPA OCCURS...BUT AT THEIR WARMEST ARE AROUND CLIMO.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE MAJORITY OF THE
FORECAST CYCLE WITH THE EXCEPTION OF POSSIBLE AFTERNOON TSRA AND
EARLY MORNING VISB/CIG RESTRICTIONS. INITIALIZED TAF WITH LIGHT
NORTHWEST WINDS AND BKN LOW VFR CU WITH A 4HR TEMPO FROM 22-02Z TO
ACCOUNT FOR AFTERNOON CONVECTION IN THE WARM SECTOR AHEAD OF AN
APPROACHING BACK DOOR FRONTAL BOUNDARY. BEYOND THAT...KEPT PROB30
IN THE NEXT FM GROUP AS LATEST CAMS INDICATED POTENTIAL FOR
REDEVELOPMENT AS THE FRONT ITSELF SLIDES THROUGH LATER THIS
EVENING. LATEST NAM RUNS SLOW THE FRONTAL PROGRESSION THROUGH THE
REGION OVERNIGHT LEADING TO PERSISTENT MVFR CIGS/VISB RESTRICTIONS
THROUGH MORNING WITH VISB IMPROVING BY LATE MORNING. KEPT
NORTHERLY WINDS AND MVFR CIGS THROUGH THE REMAINDER OF THE PERIOD
AS SOUNDINGS INDICATE CONTINUED SATURATION IN THE MOIST LOW
LEVELS.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH VFR CONDITIONS
PREVAILING THROUGH THE MAJORITY OF THE FORECAST PERIOD ASIDE FOR
AFTERNOON TSRA AND EARLY MORNING VISB/CIG RESTRICTIONS.
INITIALIZED ALL TAF SITES WITH VCTS MENTION WITH EMBEDDED TEMPO
GROUPS FOR TSRA AND 4SM VISB WITH SLIGHT TIMING DIFFERENCES
DEPENDING ON SITE LOCATION. CONTINUED WITH VCTS MENTION BEYOND
TEMPOS AT ALL SITES EXCEPT FOR KAVL AS THE FRONTAL BOUNDARY SLIDES
SOUTHEAST. FURTHER CIG AND VISB RESTRICTIONS ARE EXPECTED
OVERNIGHT AT ALL SITES...WITH GUIDANCE HITTING THE MOUNTAIN
VALLEYS THE HARDEST DESPITE THE FROPA. THUS...CARRIED MVFR
CIGS/VISB AT KAVL BUT OPTED FOR ONLY A TEMPO FOR IFR CONDITIONS
DUE TO LOW CONFIDENCE. CONDITIONS WILL IMPROVE AFTER DAYBREAK AS
HIGH PRESSURE CONTINUES TO BUILD LEADING TO THE RETURN OF VFR
AT ALL LOCATIONS ASIDE FOR KHKY WHERE LINGERING MOISTURE WILL
ALLOW FOR PERSISTENT MVFR CIGS THROUGH THE PERIOD.

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...

            12-18Z        18-24Z        00-06Z        06-12Z
KCLT       MED   67%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       MED   67%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  86%     HIGH 100%     MED   78%     HIGH  96%
KHKY       LOW   59%     HIGH 100%     HIGH 100%     HIGH  91%
KGMU       MED   79%     HIGH 100%     HIGH 100%     HIGH  95%
KAND       HIGH  82%     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...WIMBERLEY
NEAR TERM...CDG/HG/JDL
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...CDG






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