Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 211443
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1043 AM EDT SUN SEP 21 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION FROM THE NORTHWEST TONIGHT
BRINGING COOLER AIR TO THE AREA FOR THE UPCOMING WEEK. EXPECT DRY
WEATHER FOR THE WHOLE WEEK...THEN NEXT WEEKEND COULD HAVE SOME RAIN
FOR PART OF THE REGION.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1035 AM...MOSTLY CLEAR SKIES OUTSIDE OF THE MTNS WILL ALLOW
QUITE A BIT OF SUNSHINE AND HEATING TODAY BEFORE CLOUDS INCREASE
LATER THIS AFTERNOON. MTN VALLEY FOG IS DISSIPATING WITH WLY UPSLOPE
CLOUDS DEVELOPING. THE MTN CLOUDS WILL BRIEFLY DISSIPATE BEFORE
CONVECTIVE CU QUICKLY DEVELOPS. MCS ALONG COLD FRONT TO OUR WEST IS
DISSIPATING WITH LITTLE ADDITIONAL ACTIVITY ALONG THE FRONT.
GUIDANCE STILL SUGGESTS BEST PRECIP CHC ACROSS THE MTNS WHERE
MOISTURE...FORCING AND INSTABILITY WILL BE BEST. CONVECTIVE CHC
OUTSIDE OF THE MTNS IS MUCH LESS GIVEN THE RELATIVE LACK OF
MOISTURE...WLY FLOW AND LOWER INSTABILITY. CANNOT RULE OUT A SEVERE
WIND GUST FROM STORMS OVER THE MTNS GIVEN THE INCREASING SHEAR AND
DRY MID LEVELS. FCST ALREADY HAS THIS COVERED...SO ONLY MINOR
CHANGES NEEDED...MAINLY FOR CURRENT CONDITIONS.

1030 UTC UPDATE...SKY COVER HAS BEEN UPDATED PER SATELLITE IMAGERY
AND OBSERVATIONS. AREAS OF FOG HAVE BEEN ADJUSTED PER OBSERVATIONS.
WINDS WERE UPDATED TO INCORPORATE THE 06Z NAM.

AT 245 AM EDT SUNDAY...AN UPPER TROUGH WILL AMPLIFY OVER THE GREAT
LAKES TODAY...WHILE AN UPPER LOW WEAKENS AS IT MOVES UP THE CAROLINA
COAST. THE UPPER TROUGH AXIS REACHES THE EAST COAST TONIGHT...WHILE
A STRONG SHORTWAVE MOVING INTO ITS BASE APPROACHED THE SOUTHERN
APPALACHIANS.

DRY HIGH PRESSURE BETWEEN A LOW OFF THE CAROLINAS COAST AND AN
APPROACHING COLD FRONT NOW IN THE OH RIVER VALLEY WILL BREAK DOWN
THIS MORNING. THE COLD FRONT WILL REACH THE SOUTHERN APPALACHIANS BY
THIS EVENING...PRECEDED BY CONVECTION. CAPE APPEARS TO BE LIMITED TO
UNDER 1000 J/KG...ESPECIALLY EAST OF THE MOUNTAINS...BUT WIND SHEAR
AND DRY AIR ALOFT WILL BE PRESENT. GUSTY WINDS AND HAIL CANNOT BE
RULED OUT. THE FRONT CROSSES THE FOOTHILLS AND PIEDMONT THIS
EVENING. THE MODELS DIFFER SLIGHTLY ON THE TIMING OF THE
BOUNDARY...BUT BY DAYBREAK MONDAY IT APPEARS TO BE JUST ABOUT OUT OF
OUR AREA.

HIGH TEMPERATURES TODAY WILL RUN SEVERAL CATEGORIES ABOVE NORMAL IN
WARM ADVECTION AHEAD OF THE FRONT. MINIMUM TEMPERATURES WILL RUN A
BIT ABOVE NORMAL AS POST FRONTAL WINDS REMAIN UP AND SOME CLOUD
COVER LINGERS.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 2 AM EDT SUNDAY...THE SHORT TERM FORECAST PERIOD INITIALIZES
MONDAY MORNING AT 12Z WITH THE COLD FRONT MOVING SE ACROSS THE AREA.
THE NAM RETAINS SIGNIFICANTLY MORE CLOUDS AND PRECIP ASSOCIATED WITH
THE FRONTAL PASSAGE THAN THE OTHER MODELS. ASSUMING THAT THE NAM IS
THE OUTLIER MODEL IN THIS CASE...HAVE DECIDED TO KEEP ANY CHANCE OF
PRECIP OUTSIDE OF THE MOUNTAINS AT A VERY MINIMUM ONLY SLIGHT POP
FOR FAR SE COUNTIES OF THE CAROLINA PIEDMONT MONDAY MORNING. DRY AIR
FILTERS IN FOR THE REST OF THE DAY AS THE SURFACE HIGH TO OUR NORTH
EXERTS MORE INFLUENCE INTO OUR REGION INTO MID WEEK. IF THE SLOWER
SOLUTION OF FRONTAL PASSAGE ON THE NAM BECOMES THE END
VERSION...THEN WE WILL HAVE TO INCREASE POPS A BIT ALONG AND SE OF
I-85 ON MONDAY. TEMPS WILL BE COOLING GOING FROM JUST A COUPLE OF
DEGREES BELOW NORMAL MONDAY TO TWO CATEGORIES BELOW NORMAL INTO MID
WEEK.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 145 AM SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z ON
WEDNESDAY UNDER AN UPPER RIDGE WITH SURFACE HIGH PRESSURE OVER NEW
ENGLAND AND A COOL NE FLOW INTO OUR REGION. ALTHOUGH BOTH THE GFS
AND ECMWF ARE VERY SIMILAR WITH A BROAD UPPER RIDGE FROM THE ROCKIES
TO THE EAST...THERE ARE MORE DIFFERENCES BY DAY 7. THE RIDGE WILL
HOLD OVER THE EAST WHILE A TROUGH DIGS ACROSS THE WESTERN STATES
DAYS 6 AND 7.

AT THE SURFACE...STRONG CANADIAN HIGH PRESSURE WILL BE CENTERED TO
OUR NORTH WITH COOL AND DRY AIR OVER THE FCST AREA. FOR THURSDAY AND
FRIDAY THE CENTER OF THE HIGH SHIFTS A BIT EAST WITH THE WIND GOING
FROM NE TO FROM A MORE EASTERLY DIRECTION WITH A MOIST FETCH OFF THE
ATLANTIC. THIS FLOW WILL CREATE AN INCREASE IN CLOUDS AND BRING
SLIGHT POPS TO THE EASTERN AND SOUTHERN FORECAST ZONES. THUS...THE
SLIGHT CHANCE POPS WILL INITIALLY BE OVER THE PIEDMONT...THEN OVER
THE WEEKEND THE FLUX OF MOISTURE SHOULD AFFECT NE GA AND THE UPSTATE
MORE THAN THE NC PIEDMONT. THE GFS HAS A PLUME OF MOISTURE ROTATING
NORTH FROM THE EASTERN GULF OVER THE WEEKEND MOVING ACROSS AL AND GA
THEN INTO TN BY SATURDAY NIGHT. THE EC ON THE OTHER HAND IS DRIER
FOR OUR REGION OVER THE WEEKEND...BUT CERTAINLY SHOWS A LARGE PLUME
OF MOISTURE MOVING NORTH FROM THE GULF SATURDAY NIGHT...BUT FARTHER
WEST THAN THE GFS MOISTURE PLUME.

ALTHOUGH WE WILL BE UNDER AN UPPER RIDGE THROUGH THIS PERIOD...THE
COOL SURFACE HIGH TO OUR NORTH WILL KEEP TEMPS A FEW DEGREES BELOW
NORMAL FROM DAY 4 THROUGH DAY 7.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ALL BUT KAVL...VFR. CLEAR SKIES WILL GIVE WAY TO
DEVELOPING CONVECTIVE CU THIS AFTERNOON. QUESTIONABLE WHETHER ANY
LOW VFR CIGS DEVELOP GIVEN THE DEVELOPING WLY FLOW...BUT MID AND/OR
HIGH CLOUD CIG LIKELY. THE CHANCE OF CONVECTION TODAY AND TONIGHT IS
NOT GREAT ENOUGH TO MENTION. LIGHT WNW WINDS WILL BACK TO WSW AND
INCREASE TODAY...VEERING NW BEHIND THE FRONT LATE TONIGHT. WINDS
WILL STAY UP AHEAD OF THE FRONT THIS EVENING...AND BEHIND IT
OVERNIGHT.

AT KAVL...FOG IS DISSIPATING...ALONG WITH WLY UPSLOPE CLOUDS.
CONVECTIVE CU DEVELOPS THRU AFTERNOON...WITH LOW VFR CIG POSSIBLE.
COLD FRONT MOVING IN BRINGS CHC OF CONVECTION THIS AFTERNOON AND
EVENING. KAVL HAS THE BEST CHC OF ANY TAF SITE FOR SEEING
CONVECTION...SO MAY HAVE TO ADD FOR THE 18Z TAF. NW WIND WILL
INCREASE TODAY AND REMAINING UP LATE TONIGHT. MODEL TIME HEIGHTS
SUGGEST AN MVFR CIG LATE TONIGHT IF ENOUGH CLOUD COVER REMAINS
BEHIND THE DEPARTING FRONT.

OUTLOOK...HIGH PRESSURE BUILDS BACK IN EARLY NEXT WEEK WITH VFR
CONDITIONS. MOISTURE MAY RETURN FROM THE COAST BY LATE IN THE WEEK.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-14Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  86%     LOW   48%
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...DEO
NEAR TERM...JAT/RWH
SHORT TERM...DEO
LONG TERM...DEO
AVIATION...JAT/RWH





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