Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 312316
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
716 PM EDT TUE MAR 31 2015

.SYNOPSIS...
HIGH PRESSURE WILL SLIDE EAST OF THE AREA TONIGHT AS A WEAK COLD
FRONT PASSES OVER THE CAROLINAS OVERNIGHT. SURFACE RIDGING WILL
QUICKLY BUILD AGAIN FOR WEDNESDAY WHILE PRECIPIATION CHANCES
INCREASE ON THURSDAY AS MOIST SOUTHERLY FLOW RETURNS. YET ANOTHER
COLD FRONT IS EXPECTED TO APPROACH THE CAROLINAS FRIDAY EVENING WITH
HIGH PRESSURE RETURNING FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
2315 UTC UPDATE...WINDS WERE UPDATED TO INCORPORATE THE LATEST NAM
MODEL DATA. POPS WERE UPDATED FROM RADAR TRENDS...AND SKY COVER
WAS UPDATED FROM SATELLITE IMAGERY.

AS OF 230 PM...LATEST SATELLITE IMAGES INDICATED SUNNY CONDITIONS
ACROSS THE FORECAST AREA...A FEW CU OVER GRAHAM COUNTY. LATEST
MESOSCALE ANALYSIS INDICATE THAT THE FORECAST AREA WAS CAPE FREE.
HOWEVER...LOW VALUES EXISTED ACROSS EASTERN TN SOUTH ACROSS AL AND
NW GA. RECENT RUNS OF CAMS INDICATE THAT CONVECTION THE DEVELOP
ALONG AN OLD FRONT ACROSS THE I-20 CORRIDOR WILL TRACK
SOUTHEAST...MISSING THE UPPER SAVANNAH RIVER VALLEY. GIVEN THE
CURRENT SATELLITE TRENDS...IT APPEARS THE CAMS ARE CORRECT.
OTHERWISE...DEEP MIXING SHOULD PROVIDE GUSTS AROUND 20 KTS THROUGH
EARLY THIS EVENING. WINDS SHOULD DECOUPLE AROUND 1Z...SETTLING FROM
THE SW SLIGHTLY BELOW 10 KTS.

TONIGHT...NEAR TERM MODELS INDICATE THAT A COLD FRONT ASSOCIATED
WITH A MID ATLANTIC CLIPPER WILL REACH THE SOUTHERN APPALACHIANS
AROUND 0Z...PASSING SOUTH OF THE NC/SC LINE BY 6Z. AS THE FRONT
ENCOUNTERS THE MTNS THIS EVENING...WEAK CAPE MAY POOL ACROSS THE
TN BORDER COUNTIES OF NC. THE 12Z 4KM WRF INDICATES THAT WEAK
SHOWERS/THUNDERSTORMS DEVELOP ALONG THE SPINE OF THE APPALACHIANS
BETWEEN 3Z TO 8Z. THE NAM AND GFS ARE GENERALLY ON BOARD WITH THE 4
KM WRF. HOWEVER...GIVEN LOW DEWPOINTS AND NEARLY ZERO CAPE THIS
AFTERNOON...I ASSUME THAT INSTABILITY WILL STRUGGLE TO EXIST PAST
MIDNIGHT. I WILL INDICATE CHC TO SCHC ACROSS THE TN BORDER COUNTIES
THIS EVENING...WITH NO MENTION AFTER 5Z. FOG WILL BE POSSIBLE
ANYWHERE THAT RAIN FALLS. LOW TEMPERATURES ARE FORECAST TO RANGE
FROM THE U30S TO LOW 40S ACROSS THE MTNS TO AROUND 50 ACROSS THE
UPSTATE AND NE GA.

WEDNESDAY...WEAK HIGH PRESSURE SHOULD BUILD SOUTH ACROSS THE WESTERN
CAROLINAS DURING THE DAYLIGHT HOURS. LIGHT NORTH-NORTHEAST WINDS ARE
FORECAST TO DEVELOP DURING THE PRE DAWN HOURS AND REMAIN THROUGH THE
DAY. RISING MID LEVEL HEIGHTS AND LINGERING LOW BL DEWPOINTS WILL
YIELD DRY CONDITIONS ACROSS THE REGION. HIGH TEMPERATURES SHOULD
RANGE FROM THE MID 60S WITHIN THE MTN VALLEYS TO LOW TO MID 70S
ALONG AND EAST OF I-85.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 300 PM EDT TUESDAY...SHORT TERM BEGINS WITH RISING THICKNESSES
ACROSS THE SOUTHEAST AS WEAK RIDGING ALOFT BUILDS IN. NORTHWEST FLOW
OVER THE WESTERN CAROLINAS WILL HELP TO PUSH THE SURFACE HIGH
PRESSURE FARTHER OFFSHORE AS ANOTHER SHORTWAVE DIGS INTO THE MID
SOUTH. WAVETRAIN SLIDES QUICKLY EAST DURING THE DAY ON THURSDAY AND
SHORTWAVE DAMPS SOMEWHAT AS IT PUSHES INTO THE SOUTHEAST...BUT STILL
ENOUGH FOR ALL GUIDANCE TO DEVELOP SHOWERS AND THUNDERSTORMS ACROSS
THE SOUTHERN APPALACHIANS. FINGER OF STABILITY PERSISTS JUST IN THE
LEE OF THE MOUNTAINS BUT BOTH NAM AND GFS INCREASE SBCAPE VALUES
ACROSS UPSTATE SOUTH CAROLINA AND NORTHEAST GEORGIA... WITH NAM
PUSHING UPWARDS OF 2000 J/KG. GFS SUBSTANTIALLY LOWER THAN THAT WITH
ONLY LIMITED SBCAPE VALUES PUSHING INTO THE FORECAST AREA. HAVE
TRIED TO REFLECT A COMPROMISE WHICH SEEMS TO BE IN DECENT AGREEMENT
WITH SPC DAY3 CONVECTIVE OUTLOOK...BRINGING GENERAL THUNDER INTO THE
WEST AND SOUTHWEST PORTIONS OF THE FORECAST AREA. WEAK DEEP-LAYER
SHEAR /GENERALLY LESS THAN 35KT 0-6KM/ COINCIDES WITH THESE
ENCROACHING SBCAPE VALUES SO WHILE AT THIS TIME SEVERE THUNDERSTORMS
ARE NOT ANTICIPATED...EVOLUTION OF THE SHORTWAVE WILL HAVE TO BE
MONITORED IN SUBSEQUENT FORECASTS. SHOULD SEE A BIT OF LOWERING HIGH
TEMPS FOR THURSDAY AFTERNOON IN RESPONSE TO THE FALLING HEIGHTS
ASSOCIATED WITH THE SHORTWAVE ITSELF AS WELL AS INCREASED CLOUD
COVER.

SHORTWAVE PUSHES THROUGH THURSDAY NIGHT INTO FRIDAY MORNING LEAVING
WEAK NEAR ZONAL FLOW ALOFT OVER THE AREA ON FRIDAY. SOUTHERLY
SURFACE FLOW WILL CONTINUE TO PUMP MOISTURE ESPECIALLY INTO THE
PIEDMONT WITH HIGHS AGAIN REACHING WELL ABOVE SEASONAL NORMALS
ACROSS THE AREA. MEANWHILE ANOTHER MORE SIGNIFICANT TROUGH DIPS OUT
OF CANADA INTO THE MIDWEST AND GREAT LAKES...DRAGGING A COLD FRONT
ALONG WITH IT. SOME CONCERN STILL ON TIMING WITH THE GFS 6-12 HOURS
FASTER THAN THE ECMWF /THIS HAS BEEN THE TREND FOR THE PAST FEW
RUNS/ BUT IN ANY CASE SHOULD START TO SEE AN INCREASE IN POPS LATE
IN THE SHORT TERM PERIOD ESPECIALLY ACROSS THE MOUNTAINS AS THE
INFLUENCE OF THE FRONT PUSHES INTO THE FORECAST AREA.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 330 AM EDT TUESDAY...THE MEDIUM RANGE FCST PERIOD INITIALIZES
FRIDAY MORNING AHEAD OF A COLD FRONT PUSHING SOUTHEAST THROUGH THE
OH VALLEY INTO THE TN VALLEY REGION.  A SURFACE WAVE DEVELOPING
ALONG THE FRONTAL AXIS WILL DEEPEN AS SOUTHERLY FLOW OVER THE
SOUTHEAST SETS UP AN IMPROVING WARM SECTOR WHERE DEWPOINTS ARE FCST
TO SURGE INTO THE UPPER 50S TO LOWER 60S WITH SURFACE TEMPERATURES
FCST IN THE 70S TO NEAR 80.  AS DIURNAL HEATING MAXIMIZES...WOULD
NOT BE SURPRISED TO SEE SCATTERED CONVECTION ON FRIDAY AHEAD OF THE
FRONT...AS DEPICTED ON BOTH THE GFS/ECMWF.  THAT SAID...MODELS FAVOR
QUITE A BIT OF MOISTURE IN THE MID/UPPER LEVELS LIMITING LAPSE
RATES...THUS DAMPENING THE POTENTIAL FOR DEEP/ORGANIZED CONVECTION
DESPITE MODEST SHEAR THROUGH THE PROFILE.  FCST FEATURES CHANCE
LEVEL POPS ACROSS THE EAST WHILE INCREASING LIKELY POPS ARE FAVORED
OVER THE MTNS WITH THUNDER MENTIONED REGIONWIDE.  THE FRONT WILL
PUSH THROUGH THE REGION DURING THE EVENING HOURS WITH AN ADDITIONAL
ROUND OF SHOWERS/THUNDERSTORMS POSSIBLE ALONG AND JUST BEHIND THE
FRONTAL AXIS.  BY THAT TIME EXPECTING INSTABILITY TO BE AT A PREMIUM
THEREFORE ONLY ISOLATED/SCATTERED THUNDERSTORMS LOOK FEASIBLE AT
THAT POINT.  HIGH PRESSURE WILL SPILL IN SHARPLY ON SATURDAY MORNING
FROM THE WEST LEADING TO A DRYING FCST FOR THE REMAINDER OF THE
WEEKEND AMONGST NEAR NORMAL TEMPERATURES AND MOSTLY SUNNY SKIES.
THE NEXT ROUND OF WEATHER IS FCST ON MONDAY AS ANOTHER WEAK
SHORTWAVE SLIDES THROUGH THE TN VALLEY INTO THE SOUTHERN APPS.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
AT KCLT...VFR. SKY COVER WILL INCREASE SOMEWHAT OVERNIGHT AS A COLD
FRONT APPROACHES...BUT NOT ENOUGH FOR A LOW VFR CIG. THE WIND WILL
VEER FROM SW TO NW TONIGHT...AND NE BY DAYBREAK...BUT WILL REMAIN
RATHER LIGHT. MODEL GUIDANCE DOES NOT SUPPORT A VSBY RESTRICTION.

ELSEWHERE...VFR. SKY COVER WILL INCREASE AHEAD OF AN APPROACHING
FRONT...BUT ENOUGH FOR A LOW VFR CIG AT KAVL ONLY. FOOTHILLS WINDS
WILL VEER FROM SW TO NW THIS EVENING...THEN NE BY DAWN....AND SE ON
WEDNESDAY AFTERNOON. KAVL WINDS WILL BO NW EARLY AND REMAIN THERE
UNTIL WEDNESDAY AFTERNOON WHEN THEY GO SE AS WELL.

OUTLOOK...AN APPROACHING WARM FRONT AND RESULTANT MOISTURE RETURN
WILL BRING BETTER CHANCES FOR PRECIP/RESTRICTIONS ACROSS THE AREA
LATER IN THE WEEK...PERHAPS STARTING THURSDAY MORNING. A COLD FRONT
WILL AFFECT THE AREA FRIDAY INTO EARLY SATURDAY...BRINGING ANOTHER
ROUND OF RAIN/POSSIBLE THUNDERSTORMS AND RESTRICTIONS. VFR WILL
RETURN FOR THE REST OF THE WEEKEND.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     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%     HIGH 100%     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...JPT
NEAR TERM...JAT/NED
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...NED


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