Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 202153
AFDGSP

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

.SYNOPSIS...
UNSETTLED WEATHER WILL CROSS THE AREA LATE TONIGHT INTO THURSDAY
WITH THE PASSING OF A 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 THURSDAY/...
AS OF 550 PM...LATEST RADAR IMAGES INDICATED A FEW SHOWERS ACROSS
THE ESCARPMENT...PRIMARILY FROM POLK COUNTY WEST INTO NE GA. THESE
SHOWERS HAVE DEVELOPED IN THE VICINITY OF A WARM FRONT. NORTH OF THE
FRONT...ACROSS THE I-40 CORRIDOR DEWPOINTS RANGED IN THE U30S...WITH
DEWPOINTS IND THE MID TO U60S ACROSS THE UPPER SAVANNAH RIVER
VALLEY. LATEST SPC MESOSCALE ANALYSIS INDICATED CAPES ABOVE 500 J`KG
ACROSS THE UPSTATE...WITH NEAR ZERO ACROSS I-40. I WILL EXPAND CHC
POPS ACROSS THE HIGH TERRAIN ALONG THE CAROLINA BORDER AND NE GA
THROUGH EARLY THIS EVENING. IN ADDITION...I WILL INCREASE CHC POPS
ACROSS THE WESTERN NC MTNS A LITTLE EARLIER...BASED ON RADAR TRENDS
OVER MIDDLE TN. IN ADDITION...OBSERVED TEMPERATURES RANGE A LITTLE
WARMER THAN FORECAST...I HAVE ADJUSTED HRLY TEMPS AND DEWPOINTS.


AS OF 245 PM EDT WEDNESDAY...A WEAK UPPER SHORTWAVE CONTINUES TO
SLIDE THROUGH THE OH/TN VALLEYS AT THIS TIME AMIDST NEARLY ZONAL H5
FLOW.  AT THE SURFACE...A COLD FRONT ASSOCIATED WITH SAID UPPER WAVE
IS SLIDING EAST THROUGH CENTRAL ARKANSAS.  CLOSER TO HOME...REMNANT
COLD FRONTAL PASSAGE FROM TUESDAY HAS BEGUN TO LIFT NORTHWARD AS A
WARM FRONT WITH DEWPOINTS GRADUALLY INCREASING.  RECENT OBS AROUND
THE REGION INDICATE DEWPOINTS IN THE UPPER 40S ALONG AND NORTH OF
I40...WITH DEWPOINTS INCREASING FURTHER SOUTH TOWARD THE I85
CORRIDOR.  IN RESPONSE...THE 18Z MESOANALYSIS INDICATES MINIMALLY
INCREASING CAPE OVER THESE AREAS.  THUS...CONTINUED WITH AN ISOLATED
POP MENTION OVER THE CLIMO FAVORED REGIONS OF THE UPPER FRENCH BROAD
VALLEY...AND ALSO PORTIONS OF THE I85 CORRIDOR.

BEYOND THAT THE FOCUS SHIFTS TO THE ABOVE MENTIONED UPPER WAVE AS IT
APPROACHES FROM THE WEST.  MODELS CONTINUE TO PROG A DYING BAND OF
CONVECTION SLIDING INTO THE NC HIGH TERRAIN OVERNIGHT...BEFORE
PUSHING THROUGH THE REMAINDER OF WESTERN NC THROUGH MID/LATE
MORNING.  EXPECTING CONVECTION TO REINITIATE OVER THE NC PIEDMONT AS
THE PRIMARY UPPER VORT MAX SLIDES BY TO THE NORTH BY AROUND DAYBREAK
THURSDAY...WITH ENOUGH INSTABILITY IN/AROUND THE REGION TO PROMOTE A
FEW THUNDERSTORMS.  ALL IN ALL IT LOOKS RATHER UNEVENTFUL AS THE
FRONT ADVECTS THROUGH THE AREA BY 14Z-15Z WITH SURFACE FLOW VEERING
SHARPLY WEST/NORTHWEST AS HIGH PRESSURE SLIDES IN.  INCREASED
PRESSURE GRADIENT ALONG WITH MIXING OF ENHANCED LOW LEVEL WINDS WILL
LIKELY PROMOTE SOME GUSTS EARLY ON IN THE DAY...AMONGST CLEARING
SKIES.  TEMPERATURES THROUGH THE PERIOD WILL COOL SLIGHTLY BEHIND
THE COLD FRONTAL PASSAGE...HOWEVER SHOULD REMAIN ABOVE NORMAL.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 215 PM WED...THE SHORT RANGE SHAPES UP TO BE FAIRLY QUIET. A
SHORT WAVE WILL PASS BY WELL TO THE N ON THURSDAY EVENING...WHICH
SHOULD PUSH THE UPPER TROF AXIS ACROSS THE WESTERN CAROLINAS/NE
GEORGIA OVERNIGHT. SOME RESIDUAL MOISTURE MAY GET FORCED UP THE W
SIDE OF THE MTNS BY THE NW FLOW...BUT THAT SHOULD NOT AMOUNT TO MUCH
MORE THAN A SMALL CHANCE OF SHOWERS THAT WOULD TAPER OFF BY
MIDNIGHT. FROM THAT POINT ONWARD...THE UPPER PATTERN EVOLVES SLOWLY
WITH A RIDGE AXIS TO THE WEST THROUGH THE END OF SATURDAY. THAT
SHOULD TAKE SURFACE HIGH PRESSURE SLOWLY PAST TO THE NORTH ON FRIDAY
AND SATURDAY...PERHAPS REACHING THE MID ATLANTIC COAST BY SUNSET
SATURDAY. MOISTURE RETURN IS NOT EXPECTED AS THE UPPER RIDGE AXIS
REMAINS WELL TO THE WEST. THUS...EXPECT DRY WEATHER AND NORMAL TEMPS
FOR BOTH FRIDAY AND SATURDAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 205 PM EDT WED...A STRONG ULVL RIDGE WILL CONTINUE TO BUILD
ACROSS THE ERN CONUS SAT NIGHT WITH THE AXIS MOVING OF THE EAST
COAST BY LATE MONDAY. THE GFS H5 Z ENS MEAN AGREES WELL WITH THE OP
MODEL PROGRESSIONS AND VERY LITTLE MEMBER SPREAD IS SEEN ACROSS THE
SE/RN STATES THROUGH MOST OF THE PERIOD. IN THE LOWER LEVELS...A
STRENGTHENING BERMUDA HIGH WILL MAINTAIN A RIDGE ACROSS THE
CAROLINAS SUN/MON BEFORE BREAKING DOWN TUE/WED AS A UPPER S/W AND
COLD FRONT APPROACHES FROM THE WEST.

THERE ISN/T MUCH CHANGE IN THE SENSIBLE WX FCST FROM THE PREVIOUS
PACKAGE. THE BEST GOM MOISTURE FLUX WILL BE MAXIMIZED WEST OF THE
CWFA INTO MON...BEFORE ADDED ATL MOISTURE BEGINS TO ADVECT FROM THE
SE. MODEL SOUNDINGS SHOW A PERSISTENT MLVL SUBS INVERSION INTO MON
AS WELL...SO ANY CONVEC ACTIVITY SHOULD REMAIN RELEGATED ACROSS THE
HIGHER TERRAIN AND SHUNTED WITH DEEPER SHOWERS DEVELOPING MON
AFTERNOON IN LOCALIZED MECH LIFT...POSSIBLY PRODUCING A FEW TSTMS.
POPS REMAIN SLIGHT TO LOW END CHANCE THROUGH MON...WITH AN INCREASE
TO MID RANGE MTN POPS TUE/WED AS THE SUBS PATTERN WEAKENS IN A
DIURNALLY DESTABILIZING ATMOS. TEMPS WEREN/T CHANGED MUCH...STILL
EXPECT A MODEST INCREASE EACH AFTERNOON WITH MAXES ARND 10 DEGREES
ABOVE NORMAL BY WED.

&&

.AVIATION /22Z 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...

            22-04Z        04-10Z        10-16Z        16-18Z
KCLT       HIGH 100%     HIGH 100%     MED   67%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     MED   63%     HIGH 100%
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...SBK
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...SBK
AVIATION...CDG



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