Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201806
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
206 PM EDT WED MAY 20 2015

.SYNOPSIS...
DRY HIGH PRESSURE WILL BUILD ACROSS THE REGION TODAY. BRIEFLY
UNSETTLED WEATHER WILL RETURN FROM THE WEST LATE TONIGHT INTO
THURSDAY WITH A PASSING COLD FRONT. DRIER CANADIAN HIGH PRESSURE
WILL BUILD OVER THE CAROLINAS AND NORTHEAST GEORGIA FRIDAY AND
REMAIN THROUGH THE WEEKEND. SOUTHERLY FLOW MOISTURE AROUND BERMUDA
HIGH PRESSURE WILL GRADUALLY RETURN EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 200 PM EDT WEDNESDAY...LATEST SPC MESOANALYSIS INDICATES
SLOWLY IMPROVING INSTABILITY FIELD ACROSS THE UPSTATE AND DEWPOINTS
INCREASE FROM THE SOUTH.  CONVECTION ACROSS THE MIDLANDS SHOULD
REMAIN IN PLACE THIS AFTERNOON...HOWEVER A NON ZERO CHANCE FOR
SHOWERS DOES EXIST OVER PORTIONS OF THE SOUTHWEST NC MTNS AND THE
I85 CORRIDOR.  THUS...OPTED TO ONLY MAKE SLIGHT TWEAKS TO THE POPS
FOR THIS AFTERNOON.  OTHERWISE ADJUSTED TEMPS/DEWS ALONG WITH SKY
ALL THE WHILE LEAVING ALL ELSE AS IT WAS.  FULL FCST DISCUSSION TO
FOLLOW WITHIN THE HOUR.

PREVIOUS DISCUSSION...

A COLD FRONT HAS NOW SAGGED INTO THE UPSTATE AND MAY MAKE SLIGHTLY
FURTHER PROGRESS BEFORE STALLING OUT ACRS MIDDLE GA AND SRN SC LATER
TODAY. NEARLY ZONAL UPPER FLOW WILL BE PRESENT ALOFT. THE
ATMOSPHERIC COLUMN WILL BE QUITE A BIT DRIER OVER OUR AREA THAN IT
HAS BEEN OF LATE...AND THOUGH LAPSE RATES REMAIN AT LEAST MARGINALLY
SUPPORTIVE OF CONVECTION...THIS IS EXPECTED TO REMAIN ISOLATED AND
GENERALLY ALONG OR SOUTH OF THE NC BORDER WHERE DEWPTS WILL BE
HIGHEST. THAT SAID ANY STORMS THAT DO FORM MIGHT BE CAPABLE OF
STRONG WIND GUSTS GIVEN DRIER PROFILES. MOSTLY SUNNY SKIES ARE
ANTICIPATED...AND WITH THICKNESSES HAVING TAKEN ONLY A SLIGHT HIT
DUE TO THE FRONT...TEMPS AGAIN SHOULD PEAK SEVERAL DEGREES ABOVE
CLIMO. HUMIDITY WILL BE A BIT MORE COMFORTABLE HOWEVER.

MEANWHILE...A SHORTWAVE WILL MOVE OUT OF THE PLAINS AND INTO THE
OH/TN VALLEYS BY 00Z. AHEAD OF THIS FEATURE A WEAK SFC WAVE WILL
DEVELOP ALONG WHAT AMOUNTS TO A SECONDARY COLD FRONT SAGGING SWD. AS
THE SFC WAVE MOVES INTO OUR AREA THIS EVENING IT WILL GENERATE SOME
ISENTROPIC LIFT AND BRING SOME MOISTURE BACK OVER THE OLD FRONT.
ALSO...SOME ELEVATED CONVECTION COULD BE KICKED OFF. POPS WILL
INCREASE ACRS THE AREA FROM WEST TO EAST OVERNIGHT...WITH THE BEST
CHANCES IN THE MTNS...AND NRN FOOTHILLS/PIEDMONT. MIN TEMPS WILL
REMAIN SEVERAL DEGREES ABOVE NORMAL UNDER CLOUD COVER.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 245 AM EDT WED...BROAD HEIGHT FALLS WILL OCCUR ACROSS THE EAST
THU INTO THU NIGHT AS A TROUGH EXTENDING SOUTHWARD FROM QUEBEC
BOTTOMS OUT ACROSS THE CAROLINAS. PROFILES WILL BE FAIRLY DRY UNDER
THIS TROUGH...BUT SOME DEGREE OF SFC TO 850 MB MOISTURE WILL
ACCOMPANY A PASSING FRONTAL ZONE EARLY THU. THE BEST FORCING AND
MOISTURE FOR SCATTERED SHOWERS WILL OCCUR THU MORNING ACROSS THE NRN
TIER...WITH THE BETTER INSTABILITY FOR ANY AFTN AND EVENING SHOWERS
AND THUNDERSTORMS SHUNTED WELL TO THE EAST ACROSS THE COASTAL PLAIN.
MAXES WILL HOVER NEAR CLIMO IN THE MTNS THU AFTN...AND ABOUT A
CATEGORY OR SO ABOVE TO THE EAST. EXPECT ANY RESIDUAL UPSLOPE
SHOWERS TO QUICKLY DISSIPATE IN THE WRN MTNS THU NIGHT...WITH COOLER
TEMPERATURES SETTLING IN TO PRODUCE PLENTY OF 40S MTNS TO 50S
PIEDMONT.

HEIGHTS WILL BEGIN RISING AGAIN FROM THE WEST ON FRIDAY. DRY
PROFILES WILL BE IN PLACE...WITH MAX TEMPS FALLING ABOUT 5 DEGREES
BELOW CLIMO DURING A COMFORTABLE FRIDAY AFTERNOON.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 245 AM EDT WED...A DOMINANT RIDGE WILL SET UP OVER THE
SOUTHEAST THROUGH THE WEEKEND. IN ADDITION...SFC HIGH PRESSURE
BUILDING SWD FROM CANADA ON SAT WILL SEND A WEAK BACKDOOR COLD FRONT
INTO THE REGION WITH LITTLE OR NO ATTENDANT MOISTURE. ANY DEEPER
MOISTURE WILL GENERALLY STAY W OF THE SRN APPALACHIANS THROUGH THE
WEEKEND...BUT WITH A LOW LEVEL ATLANTIC FETCH GRADUALLY MODERATING
THE CP AIRMASS IN PLACE. ISOLD DIURNAL SHOWERS WILL BE POSSIBLE IN
THE SRN MOUNTAINS LATE SUNDAY...WITH TEMPERATURES WARMING BACK ABOVE
CLIMO.

THE RIDGE AXIS WILL MIGRATE OFFSHORE EARLY NEXT WEEK...BUT WITH ANY
PHASING TROUGHS TO THE WEST LIFTING MAINLY N OF THE OH VALLEY
THROUGH TUE. MOISTURE WILL CONTINUE TO GRADUALLY CREEP
EASTWARD...CAUSING DIURNAL CONVECTIVE CHANCES TO INCREASE MON AND
TUE AFTN...ESPECIALLY ACROSS THE MTNS. MAX TEMPS WILL WARM BACK
THROUGH THE 80S...WITH TEMPERATURES POSSIBLY APPROACHING 90 IN THE
PIEDMONT BY TUE AFTN.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AT KCLT...PRIMARILY VFR THROUGH THE PERIOD ASIDE FOR LOW PROB
CONVECTION.  INITIALIZED TAF WITH LOW VFR CU BENEATH HIGH LEVEL
CIRRUS STREAMING IN FROM UPSTREAM CONVECTION OVER WEST TN.  ADDED A
LOW CONFIDENCE 3HR MVFR TEMPO FOR -TSRA THIS AFTERNOON AS CAM
GUIDANCE FAVORS A REGION OF INCREASING INSTABILITY OVER THE NC/SC
PIEDMONT REGION WITH LITTLE/NO CIN IN PLACE.  BEYOND THAT THE FOCUS
SHIFTS TO THE APPROACHING UPPER SHORTWAVE TROF AND FRONTAL AXIS FROM
THE WEST.  CARRIED CONTINUED LOW VFR STRATUS WITH HIGH LEVEL CIGS
THROUGH MIDNIGHT BEFORE INTRODUCING SHRA AND MVFR CIGS AROUND THE
09Z TIMEFRAME PER GUID AS CONVECTION RE-INITIATES UNDER THE PASSING
UPPER VORT MAX.  A PROB30 FOR TSRA WAS INCLUDED FROM THE 09Z/12Z
TIMEFRAME BASED UPON LATEST CAM GUIDANCE...AND NAM SOUNDINGS WHICH
INDICATE ENOUGH INSTABILITY PRESENT BENEATH SAID UPPER SUPPORT FOR A
FEW TALLER UPDRAFTS CAPABLE OF LIGHTNING.  CONDITIONS WILL IMPROVE
AS THE WAVE EJECTS NORTHEAST AND THE FRONT SLIDES THROUGH THE REGION
THURSDAY MORNING.  WINDS TODAY INITIALIZE LIGHT AND SOUTHERLY WITH
GRADUAL VEERING EXPECTED AHEAD OF THE FRONT.  WINDS WILL VEER
SHARPLY NORTHWEST AFTER DAYBREAK...POST FROPA.  FROM THERE INCREASED
PRESSURE GRADIENT FORCES CONSEQUENT OF APPROACHING SURFACE RIDGE
ALONG WITH MIXING WARRANT 15-18KT GUSTS THROUGH THE PERIOD.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH THE FCST PRIMARILY
FOCUSED ON APPROACHING UPPER/SFC WAVE AND ASSOCIATED COLD FRONT.
ALL SITES INITIALIZE VFR AMIDST FEW/SCT LOW TO MID LEVEL CU BENEATH
HIGH CIRRUS.  NEAR TERM CAM GUID CONTINUES TO HINT AT ISOLATED SHRA
OVER THE UPSTATE THIS AFTERNOON...HOWEVER CONFIDENCE IS VERY LOW
THUS OPTED NOT TO INCLUDE AT THIS TIME DUE TO UNIMPRESSIVE CU
FIELD.  THUS...ALL SITES ASIDE FOR KAVL/KHKY REMAIN DRY WITH NO WX
MENTION THROUGH THE PERIOD AS THE BEST POP IS EXPECTED OVER WESTERN
NC ASSOCIATED WITH THE APPROACHING WAVE/FRONT...WITH ONLY VCSH
CARRIED AT THESE TWO LOCATIONS ALONG WITH MVFR CIGS AT KHKY.
OTHERWISE...CONDITIONS WILL IMPROVE BEHIND THE FRONT WITH SOUTHERLY
WINDS VEERING NORTHWEST AND INCREASING WITH GUSTS LIKELY AT ALL
SITES THURSDAY MORNING...THROUGH THE PERIOD.

OUTLOOK...HIGH PRESSURE WILL BUILD OVER THE ENTIRE SOUTHEAST THROUGH
WEEKS END LEADING TO DRY WX THIS WEEKEND...LIKELY LASTING INTO
EARLY NEXT WEEK.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  87%     HIGH  80%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  95%
KHKY       HIGH 100%     HIGH 100%     HIGH  82%     HIGH  93%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     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...HG
NEAR TERM...CDG/WIMBERLEY
SHORT TERM...HG
LONG TERM...HG
AVIATION...CDG



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