Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 161850
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
250 PM EDT THU APR 16 2015

.SYNOPSIS...
A COOL AND DAMP WEDGE OF HIGH PRESSURE WILL GIVE WAY TO PROGRESSIVELY
WARMER AND DRIER AIR FRIDAY INTO SATURDAY. A WARM FRONT WILL MOVE
INTO THE REGION FROM THE SOUTHWEST SATURDAY NIGHT INTO
SUNDAY...ACCOMPANIED BY ABUNDANT MOISTURE AND MORE RAINFALL. A COLD
FRONTAL PASSAGE EARLY NEXT WEEK WILL FINALLY RESTORE DRIER
CONDITIONS.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 245 PM EDT THURSDAY...THE UPPER PATTERN CONTINUES TO BE
HIGHLIGHTED BY MOIST SW FLOW CONVEYOR BELT AROUND ROTATING CLOSED
UPPER LOW ATOP THE SOUTHERN ROCKIES...WITH WEAK...NEARLY FLAT
SHORTWAVE RIDGING ACROSS THE SOUTHEAST.  AT THE SURFACE...
SPRINGTIME CAD REGIME CONTINUES TO PREVAIL ACROSS THE SOUTHERN APPS
PROVIDING AMPLE FOCUS FOR UPGLIDE INDUCED RA/DZ OVER THE NC/SC
PIEDMONT REGIONS.  FURTHER WEST A BAND OF SHOWERS ASSOCIATED WITH A
WEAK UPPER WAVE CONTINUE TO ADVECT EAST ACROSS THE CUMBERLAND PLATEAU
THIS AFTERNOON.  AS EXPECTED...LITTLE TO NO INSTABILITY IS PRESENT
ACROSS THE WESTERN NC MOUNTAINS THEREFORE INWARD MOVING CONVECTION
IS WEAKENING AS IT APPROACHES THE WEDGE BOUNDARY...AND SHOULD
CONTINUE TO DO SO.

FOR THE REMAINDER OF THE AFTERNOON AND OVERNIGHT...FCST FEATURES
CHANCE POPS ACROSS THE PIEDMONT/FOOTHILLS ZONES WHERE MODELS PROG
THE BEST UPGLIDE WILL RESIDE.  BY EARLY MORNING POPS WILL DECREASE
OVER THE NC/SC PIEDMONT TO NON-MENTIONABLE LEVELS WHILE AT LEAST LOW
END CHANCE POPS REMAIN IN PLACE ALONG THE BLUE RIDGE.  MOST GUIDANCE
FAVORS DECREASED UPGLIDE BY MID MORNING AMIDST CALMING FLOW AND SOME
WEAK MID LEVEL DRYING PER TIME HEIGHTS.  THUS...WOULD NOT BE
SURPRISED TO SEE PATCHY DENSE FOG BY MORNING ESPECIALLY ACROSS THE
NC PIEDMONT AND IN THE WESTERN NC MTN VALLEYS.

FOR FRIDAY...ANOTHER H5 IMPULSE IS PROGGED TO EJECT FROM THE PARENT
CYCLONE TO THE WEST.  EXPECTING THIS FEATURE TO PROVIDE AT LEAST
WEAK UPPER SUPPORT DURING THE AFTERNOON AS RETURNING SOUTHERLY WAA
PREVAILS AT THE SFC.  A WEAK COLD FRONT WILL ALSO BE APPROACHING
FROM THE WEST...IMPACTING THE HIGH TERRAIN LATE IN THE DAY.  BOTH
NAM/GFS GUID INDICATE LOW LEVELS OF INSTABILITY...BUT CANT RULE OUT
A FEW SHOWERS AND OR THUNDERSTORMS.  OTHERWISE...INCREASING
DOWNSLOPING FLOW WILL ALLOW FOR MODEST DRYING BEHIND THE CAD
EROSION.  THUS THE FCST FEATURES DECREASING CLOUDINESS...WITH ONLY
SLIGHT CHANCE POPS OUTSIDE THE HIGH TERRAIN WHERE CHANCE LEVELS ARE
FAVORED.  TEMPERATURES ON FRIDAY WILL RECOVER SOMEWHAT...BUT SHOULD
REMAIN AT OR JUST BELOW NORMAL LEVELS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
AS OF 2 PM THURSDAY...ANY LINGERING SCT/ISLD DIURNAL CONVECTION IS
EXPECTED TO DIMINISH FRI EVENING...GIVING WAY TO AN UNSEASONABLY
WARM AND MOIST FRI NIGHT/SAT MORNING...WITH MIN TEMPS EXPECTED TO
AVERAGE AROUND 10 DEGREES ABOVE CLIMO. THERE ARE MIXED SIGNALS AS TO
THE EXTENT OF CONVECTIVE CHANCES SAT AFTERNOON/EVENING...AS TEMPS
ARE EXPECTED TO WARM TO 76-81 WITHIN A STILL-MOIST LOW LEVEL REGIME.
A SHORT TERM MODEL CONSENSUS DEPICTS CAPE MAXIMIZING AT AROUND 1000
J/KG DURING THE AFTERNOON...PERHAPS A LITTLE MORE UNSTABLE THAN
FRIDAY. THERE WILL ALSO BE AN INCREASING...ALBEIT WEAK SE UPSLOPE
FLOW. MEANWHILE...THE UPPER RIDGE AXIS IS EXPECTED TO BUILD OVER THE
REGION BY AFTERNOON. NEVERTHELESS...MOST OF THE SHORT TERM MODELS
PRODUCE A CONVECTIVE QPF RESPONSE DURING THE AFTERNOON...AND POPS IN
THE 20-30 PERCENT RANGE APPEAR WARRANTED ACROSS MUCH OF THE AREA...
WITH THE HIGHEST POPS FAVORED ACROSS WESTERN AREAS.

MAJOR HEIGHT FALLS ARE FORECAST ACROSS THE CENTRAL CONUS BY LATE IN
THE WEEKEND...WITH PHASING OF THE NORTHERN AND SOUTHERN STREAMS
EXPECTED...RESULTING IN A BROAD/FULL-LATITUDE TROUGH THAT WILL COVER
MUCH OF THE EASTERN HALF OF THE COUNTRY BY EARLY NEXT WEEK. AHEAD OF
ATTENDANT CYCLONE AND SURFACE COLD FRONT...A BROAD AND VERY MOIST
WARM CONVEYOR BELT AXIS IS EXPECTED TO OVERSPREAD THE SOUTHEAST SAT
NIGHT INTO SUNDAY...WARRANTING 80-90 POPS ACROSS OUR AREA DURING
THIS TIME FRAME. PWATS INCREASE TO 2-3 STANDARD DEVS ABOVE
CLIMATOLOGY DURING THIS TIME...WHILE A FAIRLY STRONG S/SE FLOW COULD
ENHANCE RAINFALL RATES NEAR THE BLUE RIDGE. MODEL FORECASTS OF
BUOYANCY AND SHEAR SUGGEST A NON-ZERO SEVERE THUNDERSTORM THREAT
DURING THIS TIME...ALTHOUGH SURFACE HIGH PRESSURE MOVING ACROSS
SOUTHEAST CANADA WILL SEND A BACK DOOR COLD FRONT THROUGH THE MID-
ATLANTIC...AND TOWARD THE CAROLINAS BY EARLY SUNDAY...POSSIBLY
SETTING THE STAGE FOR IN-SITU COLD AIR DAMMING. HOWEVER...IT REMAINS
HIGHLY UNCERTAIN AS TO HOW FAR SOUTH THE BOUNDARY WILL PUSH. EVEN IF
A LOW-END SEVERE THREAT DOES MATERIALIZE...HEAVY RAIN SHOULD BE THE
PRIMARY THREAT...ESP NEAR THE BLUE RIDGE.

THE WARM CONVEYOR BELT IS EXPECTED TO SHIFT GRADUALLY NORTHEAST OF
THE AREA SUNDAY NIGHT...AS CYCLONE BEGINS TO OCCLUDE IN THE VICINITY
OF THE GREAT LAKES. THIS SUPPORTS GRADUALLY DECREASING POPS SUNDAY
NIGHT...WITH SOLID WARM SECTOR CONDITIONS EXPECTED BY MONDAY MORNING
IN ADVANCE OF APPROACHING FRONTAL ZONE.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 230 PM THURSDAY...ON MONDAY...BOTH THE GFS AND ECMWF INDICATED
A STRONG LOW PRESSURE SYSTEM CENTERED OVER THE INTERNATIONAL BORDER
NEAR THE GREAT LAKES. DURING THE MORNING HOURS...THE ASSOCIATED WARM
FRONT IS FORECAST TO RUN SOUTH ALONG THE APPALACHIAN
MOUNTAINS...AROUND A WEAK CAD...EAST TOWARD THE NC OUTER BANKS. A
NORTH TO SOUTH ORIENTED COLD FRONT SHOULD BE PUSHING EAST ACROSS
MIDDLE KY/TN BY 12Z MON. THIS PATTERN WILL PLACE MOST OF THE
FORECAST AREA WITHIN THE WARM SECTOR...WITH AN AREA OF ERODING CAD
ACROSS THE NC PIEDMONT. THE SFC COLD FRONT IS EXPECTED TO CROSS THE
FORECAST AREA DURING THE AFTERNOON AND EVENING. THE TIMING OF THE
FRONT WILL FAVOR TEMPERATURE RANGING ABOVE NORMAL...RANGING FROM THE
MID 70S WITHIN THE MTN VALLEYS TO AROUND 80 EAST. FORECAST SOUNDINGS
FROM THE GFS AND ECMWF ARE A LITTLE INTERESTING...FEATURING CAPE
VALUES AROUND 1000 J/KG...WBZ LESS THAN 8KFT...AND SRH AROUND 70
M2/S2. GIVEN THE FRONTAL TIMING...INSTABILITY...AND SHEAR...THIS
WILL BE A CASE OF LINEAR CONVECTION CROSSING THE SOUTHERN
APPALACHIANS. I WILL FORECAST LIKELY POPS ACROSS THE MTNS TO SOLID
CHC POPS EAST OF THE MTNS. ORGANIZED SEVERE WEATHER IS
QUESTIONABLE...BUT SEVERAL HAIL EVENTS COULD OCCUR DURING THE
AFTERNOON.

MONDAY NIGHT THROUGH THURSDAY...MEDIUM RANGE MODELS INDICATE THAT
THE CENTER OF A LARGE HIGH PRESSURE AREA WILL SLIDE ACROSS THE
REGION. AT THE MID LEVELS...HEIGHTS SHOULD REMAIN GENERALLY ZONAL
ACROSS THE WESTERN CAROLINAS AND NE GA. OVERALL...TEMPERATURES
SHOULD AVERAGE VERY CLOSE TO CLIMO. ALSO...POPS WILL REMAIN LIMITED
TO LESS THAN A SCHC TUESDAY AND WEDNESDAY. WEAK RETURN FLOW IS
FORECAST TO DEVELOP ON THURSDAY...ALLOWING MOISTURE TO INCREASE
ACROSS THE CWA. I WILL FORECAST TEMPERATURES SLIGHT ABOVE NORMAL
WITH DIURNAL POPS. POP VALUES WILL RANGE FROM A CHC ACROSS THE MTNS
TO SCHC EAST.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
AT KCLT AND KHKY...MVFR/IFR AND LIFR RESTRICTIONS WILL HIGHLIGHT
THIS TAF CYCLE.  INITIALIZED TAF AT IFR WITH -RADZ AS WEAK UPGLIDE
REGIME PREVAILS WITH MOST CAM GUID FAVORING INCREASED COVERAGE
THROUGH THE AFTERNOON.  VISB WILL LIKELY BE VARIABLE DURING THIS
TIME PERIOD...BUT SHOULD REMAIN IN THE MVFR RANGE.  REMOVED ALL WX
MENTION BY 02-03Z AS BEST UPGLIDE SLIDES EAST AND SETS UP ALONG THE
BLUERIDGE.  DECREASED WINDS WILL ALLOW FOR DECOUPLING OF THE VERY
MOIST PBL...WHICH COMBINED WITH SOME DRYING IN THE MID LEVELS PER
LATEST TIME HEIGHTS...WILL LEAD TO WIDESPREAD FOG BY MORNING.
FAVORED LESS THAN 1SM IN THE TAF WITH A TEMPO FOR A 1/2SM OR LESS AT
TIMES WITH CIGS IN THE 001-003 RANGE.  CONDITIONS WILL SLOWLY
IMPROVE BEYOND SUNRISE AS THE WEDGE RETREATS AND DOWNSLOPING FLOW
COMMENCES.  THUS THE TAF FEATURES MVFR...TO VFR IMPROVEMENT BY
PERIODS IN.  AS MENTIONED ABOVE...WINDS WILL REMAIN LIGHT AND
NORTHEASTERLY OVERNIGHT BEFORE GRADUALLY BACKING AROUND TO THE SW.

ELSEWHERE...LOWER CHANCES FOR -RADZ EXIST THROUGH THE FIRST FEW FM
GROUPS AT ALL SC SITES AND KAVL...HOWEVER DID CONTINUE WITH -DZ
MENTION AT KGSP AND KGMU.  RESTRICTIONS WILL REMAIN AT MVFR LEVELS
INITIALLY...BUT WILL LOWER THROUGH THE LATE AFTERNOON WITH IFR
FAVORED THROUGH THE EVENING BEFORE LOWERING TO LIFR LEVELS BY EARLY
MORNING.  EXPECTING AREAS OF FOG TO DEVELOP BY MORNING WITH THE MOST
DENSE OF WHICH BEING IN AND AROUND THE MTN VALLEYS...AND ALSO OVER
THE SAVANNAH RIVER VALLEY.  THUS KAVL/KAND TAFS FEATURE VISB AT LESS
THAT 1/2SM WHILE KGSP/KGMU HOLD AT AROUND 2SM WITH CIGS LIKELY AT
LIFR LEVELS AT ALL SITES.  CONDITIONS WILL GRADUALLY IMPROVE TO MVFR
AT ALL SITES THROUGH LATE MORNING AS THE WEDGE ERODES...WITH VFR
FAVORED AT THE END OF THE TAF CYCLE AT KGSP/KGMU.  HELD KAND/KAVL AT
MVFR LEVELS AS SHRA WILL BE IN THE AREA DUE TO APPROACHING WEAK
FRONT OVER WESTERN NC...AND APPROACHING UPPER VORT MAX OVER THE
UPSTATE AND NORTHEAST GA.

OUTLOOK...DRIER WEATHER IS FAVORED INTO SATURDAY. DEEPER MOISTURE
WILL RETURN ALONG A WARM FRONT SAT NIGHT THROUGH SUNDAY...WITH HEAVY
RAINFALL AND WIDESPREAD RESTRICTIONS LIKELY ONCE AGAIN.
THUNDERSTORMS WILL THEN BE POSSIBLE THROUGH MONDAY AS A COLD FRONT
REACHES THE AREA FROM THE WEST.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       MED   66%     MED   67%     LOW   47%     HIGH  82%
KGSP       HIGH 100%     MED   75%     MED   71%     HIGH  90%
KAVL       HIGH  90%     HIGH  85%     HIGH  80%     HIGH  82%
KHKY       MED   61%     MED   61%     LOW   54%     MED   77%
KGMU       HIGH 100%     MED   72%     LOW   57%     HIGH  90%
KAND       HIGH 100%     MED   72%     MED   63%     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...CSH
NEAR TERM...CDG
SHORT TERM...JDL
LONG TERM...NED
AVIATION...CDG



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