Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 311939
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
339 PM EDT MON AUG 31 2015

.SYNOPSIS...
HIGH PRESSURE WILL LINGER ACROSS THE REGION EARLY THIS WEEK. WEAK
DISTURBANCES MAY RIPPLE ACROSS THE LOWER AND MIDDLE APPALACHIAN
REGION BY MID TO LATE WEEK. A COOL AND MOIST AREA OF HIGH PRESSURE
IS EXPECTED TO SETTLE ACROSS THE WESTERN CAROLINAS AND NORTHEAST
GEORGIA THIS WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
AS OF 230 PM...AN UPPER RIDGE WILL BUILD ALONG THE EAST COAST THRU
THE NEAR TERM. AT THE SFC...A RATHER NEBULOUS PRES PATTERN EXISTS
ACRS MUCH OF THE EASTERN CONUS...WITH A WEAK CENTER OF HIGH PRES
ROUGHLY ACRS THE CENTRAL APPALACHIANS OR JUST TO THE WEST. THIS SET
UP HAS TRAPPED SOME LLVL MOISTURE UNDER A STRENGTHENING MID LVL
INVERSION. THE FLOW IS SO WEAK HOWEVER...THAT THERE IS NO TRIGGER
FOR CONVECTION OR WIDESPREAD CLOUDS OTHER THAN TERRAIN EFFECTS.
THERE IS STILL A SLGT CHC OF MAINLY SHWRS ACRS THE NC MTNS...BUT THE
REST OF THE AREA SHUD BE DRY THRU TONIGHT. TEMPS WILL BE ABOUT A
CATEGORY ABOVE NORMAL...WITH PATCHY FOG AND STRATUS
EXPECTED...MAINLY IN THE MTNS.

TUESDAY...WITH THE CONTINUED UPPER RIDGING...EXPECT THE MID LVLS TO
REMAIN WARM...AND PUT A LID OF MOST DEEP CONVECTION. TEMPS LOOK TO
REBOUND TO A COUPLE CATEGORIES ABOVE NORMAL...WHILE DEWPTS WILL BE
SIMILAR TO MONDAY...IF NOT A DEG OR TWO HIGHER. SO THERE SHUD BE A
LITTLE BETTER INSTBY...DESPITE UNFAVORABLE MID LVLS. I WILL FCST
SLGT CHC TO LOW-END CHC AFTN SHWRS AND TSTMS ACRS THE MTNS AND
FOOTHILL ZONES...WHERE DIFFERENTIAL HEATING WILL BE THE MAIN
TRIGGER. THE PIEDMONT SHUD BE LARGELY DRY.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...
AS OF 330 PM MONDAY...EASTERN CONUS WILL BE UNDER THE INFLUENCE OF A
MEAN RIDGE WHICH WILL GIVE THE AREA TEMPERATURES AROUND 5 DEGREES
ABOVE NORMAL.  A WELL-DEFINED SMALL SHORTWAVE CURRENTLY OVER
INDIANA...WHICH IS CLEARLY SEEN IN WV IMAGERY...WILL PROVIDE SOME
ENHANCED CHANCES FOR THUNDER STORMS...ESPECIALLY OVER HIGHER
TERRAIN...THROUGH THURSDAY.  DUE TO THE ISOLATION OF THE INDIANA
SHORTWAVE FROM THE MEAN FLOW...PREDICTIONS OF ITS MOVEMENT MAY BE
SOMEWHAT INACCURATE...HOWEVER...MODELS SHOW SOME WEAKENING OF THE
RIDGE BY WEDNESDAY WITH THE WAVE BEING SLIGHTLY ENTRAINED INTO WHAT
BECOMES BROAD WESTERLY FLOW ALOFT...WHICH MOVES THE LOBE ACROSS THE
CWA ON WEDNESDAY.  INSTABILITY IS FORECAST TO BE HIGHER OVER THE
MOUNTAINS...BUT STILL SOMEWHAT LIMITED WITH THE BEST MODEL
INSTABILITY IN THE NAM AT AROUND 1500 J/KG OF CAPE...AND HARDLY ANY
LOW-LEVEL WINDSHEAR.  WITH A LITTLE FORCING FROM THE
SHORTWAVE...SOME ISOLATED SEVERE WIND GUSTS MAY BE POSSIBLE IN THE
AFTERNOON ON WEDNESDAY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
AS OF 230PM MONDAY...THE EXTENDED PERIOD BEGINS ON THURSDAY NIGHT
WITH AN AMPLIFYING LONGWAVE TROUGH IN THE MID-LEVELS OVER THE
PACIFIC NORTHWEST BUILDING A DOWNSTREAM RIDGE THAT EXTENDS FROM THE
SOUTHERN PLAINS TO THE GREAT LAKES AND WELL INTO CANADA. AN EAST
COAST TROUGH AXIS EXTENDS INTO THE SOUTHEAST AND LOWER MISSISSIPPI
RIVER VALLEY WHERE A RESIDUAL CLOSED-LOW CIRCULATION REMAINS TRAPPED
UNDERNEATH THE RIDGE. HEADING INTO THE WEEKEND...THE PARENT CLOSED-
LOW CENTERED OVER LABRADOR SHIFTS INTO THE ATLANTIC AS PERSISTENT
RIDGING BUILDS OVER NEW ENGLAND...LEAVING BEHIND A WEAK TROUGH OR
CYCLONIC CIRCULATION OVER THE SOUTHEAST U.S. THAT LINGERS ACROSS THE
AREA THROUGH THE END OF THE PERIOD ON TUESDAY MORNING.
THEREFORE...THE FLOW ALOFT THROUGH THE PERIOD WILL BE HIGHLY
DEPENDENT ON THE EXACT POSITIONING OF THE RESIDUAL TROUGH...BUT
SHOULD GENERALLY BE QUITE WEAK AND TRANSITION FROM NORTHERLY TO
SOUTHEASTERLY BY TUESDAY.

AT THE SURFACE...A LARGE AREA OF HIGH PRESSURE CENTERED OVER QUEBEC
BUT EXTENDING WELL SOUTHWEST INTO TEXAS WILL GRADUALLY BUILD SOUTH
INTO NEW ENGLAND UNDERNEATH A BUILDING RIDGE ALOFT. THE HIGH
PRESSURE SYSTEM WILL ANCHOR ACROSS NEW ENGLAND THROUGH SUNDAY BEFORE
SHIFTING OFFSHORE HEADING INTO EARLY NEXT WEEK.  THE PATTERN FAVORS
THE SURFACE RIDGE AXIS NOSING SE INTO THE FORECAST AREA...RESEMBLING
A COLD-AIR DAMMING SCENARIO. THE RESULTANT NORTHEASTERLY FLOW OVER
THE WEEKEND WILL VEER EASTERLY AS THE PARENT HIGH SHIFTS OFFSHORE BY
MONDAY...BUT IN EITHER CASE THE PATTERN FAVORS UPSLOPE FLOW AND WEAK
ISENTROPIC UPGLIDE OVER THE WESTERN CAROLINAS THROUGH THE END OF THE
PERIOD.

IN TERMS OF SENSIBLE WEATHER...THE ABOVE PATTERN FAVORS CHANCE POPS
FOR SHOWERS AND GENERAL THUNDERSTORMS THROUGH THE PERIOD FOR A
MAJORITY OF THE FORECAST AREA...WITH THE HIGHEST POPS FAVORING THE
MOUNTAINS.  HIGH TEMPERATURES SHOULD BE A FEW DEGREES ABOVE NORMAL
ON FRIDAY BUT WILL DROP TO A COUPLE OF DEGREES BELOW NORMAL FOR
SATURDAY THROUGH MONDAY.  WITH INCREASED OVERNIGHT CLOUD COVER
ANTICIPATED THIS WEEKEND...EXPECT LOW TEMPERATURES TO BE SLIGHTLY
ABOVE NORMAL.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
AT KCLT...A STRATOCU DECK HAS DEVELOPED ACRS THE KCLT AREA...WITH
BASES GRADUALLY LIFTING ABOVE MVFR RANGE BY 18Z. THE FCST SNDGS SHOW
THE CLOUDS SETTLING AROUND 4000 FT BY MIDAFTERNOON. FROM
THERE...GUIDANCE DIVERGES...WITH SOME KEEPING POTENTIAL LOW CLOUDS
AROUND THRU TONIGHT...WITH BASES LOWERING BACK TO MVFR. WHILE OTHERS
INDICATE MOST OF THE CLOUDS DISSIPATING AFTER SUNSET. GIVEN THE WEAK
FLOW AND EXPECTED LACK OF PRECIP TODAY...I LEANED TOWARD LESS
CLOUDS. HOWEVER...TOWARD DAYBREAK TUESDAY...STRATUS MAY DEVELOP IF
THERE IS ENUF FLOW/MOISTURE TO ALLOW DEVELOPMENT. I KEPT A FEW020
AROUND 10Z TO SHOW THAT POSSIBILITY. THE WINDS WILL BE LIGHT THRU
THE PERIOD...SO THERE IS ALSO SOME FOG POTENTIAL TUE MORNING.
OTHERWISE...VFR CONDITIONS ARE EXPECTED.

ELSEWHERE...THE UPSTATE SITES ARE MOSTLY CLEAR WITH LIGHT WINDS AT
TIME OF TAF ISSUANCE...WHILE MORE CLOUDS CAN BE SEEN OVER KAVL AND
KHKY (WITH BASES AROUND 4000-5000 FT). TONIGHT...I EXPECT MOST OF
THE CUMULUS CLOUDS TO DISSIPATE...LEAVING MOSTLY CLEAR SKIES WITH
LIGHT TO CALM WINDS. ENUF MOISTURE MAY EXIST FOR FOG AND STRATUS
POTENTIAL AGAIN TOWARD DAYBREAK...MAINLY AT KAVL. THE ATMOSPHERE IS
ONLY WEAKLY UNSTABLE IN THE MTNS...SO WHILE A FEW SHRA OR TSRA MAY
DEVELOP...I LEFT OUT ANY MENTION FROM THE KAVL TAF.

OUTLOOK...A PLUME OF GULF AND ATLANTIC MOISTURE WILL CONTINUE TO
WRAP UP ALONG THE SE COAST...GENERALLY JUST SOUTHEAST OF THE
TERMINAL FORECAST AREA...THROUGH THE WEEK. RESTRICTIONS ARE POSSIBLE
DURING PERIODS OF ANY SCATTERED SHOWERS OR THUNDERSTORMS. IN
ADDITION...LOW CLOUDS AND FOG MAY DEVELOP EACH NIGHT...ESPECIALLY IN
THE MOUNTAIN VALLEYS.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     MED   69%     HIGH  86%
KHKY       HIGH 100%     HIGH 100%     MED   75%     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

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...NED
NEAR TERM...ARK
SHORT TERM...WJM
LONG TERM...JMP/NED
AVIATION...ARK


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