Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 190829
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
429 AM EDT TUE AUG 19 2014

.SYNOPSIS...
A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD ACROSS THE
MISSISSIPPI RIVER VALLEY OVER THE NEXT FEW DAYS AND LINGER FOR THE
REST OF THE WORK WEEK...RESULTING IN ABOVE NORMAL TEMPERATURES. A
WEAK COLD FRONT WILL THEN PUSH INTO THE AREA FROM NORTHEAST LATE
FRIDAY INTO SATURDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
0830 UTC UPDATE...POPS AND QPF HAVE BEEN REDUCED EARLY ON PER RADAR
TRENDS. SKY COVER WAS UPDATED FROM INFRARED SATELLITE IMAGERY...
RESULTING IN A DECREASE IN CLOUD COVER. ACTIVITY IN NW GA...THROUGH
DIMINISHED...IS STILL HEADED THIS WAY.

AT 330 AM EDT TUESDAY...AN UPPER TROUGH EXTENDED FROM A CLOSED UPPER
LOW OVER THE GREAT LAKES...TO GA. MEANWHILE...AN UPPER RIDGE AXIS
STRETCHED FROM TX TO THE NORTHER ROCKIES. A STATIONARY FRONT WAS
LOCATED FROM VA TO MO...AND ANOTHER FROM CHESAPEAKE BAY TO THE GREAT
LAKES. SATELLITE IMAGERY SHOWS CLUSTERS OF CLOUD COVER FROM THE
CAROLINAS AND GA TO THE NORTHERN GULF STATES...MAINLY ASSOCIATED
WITH VORT MAXES MOVING THROUGH THE TROUGH AXIS.

THE TROUGH AXIS IS EXPECTED TO MOVE VERY SLOWLY TO THE CAROLINA
COAST BY TONIGHT. A SHORTWAVE NOW OVER AL WILL REACH THE UPPER
SAVANNAH RIVER BY DAYLIGHT...BUT AT A TIME OF MINIMUM INSTABILITY.
SHOWER ACTIVITY IN N AL MAY SURVIVE TO REACH OUR AREA BY DAWN.

THE SHORTWAVE WILL MOVE EAST OF OUR AREA BY AFTERNOON...WHILE A
WEAKER SHORTWAVE MOVES ACROSS AL AND GA. CONVECTIVE ACTIVITY WILL BE
BEST DURING MAXIMUM HEATING THIS AFTERNOON...BUT THE TIMING OF THE
TWO SHORTWAVES MAY NOT LEND IDEAL SUPPORT. MODEL SOUNDINGS SHOW A
VERY MOIST COLUMN FROM 850 MB UP TO 500 MB...WITH A DRY LAYER
BENEATH...BUT CAPE IS EXPECTED TO BE UNDER 1000 J/KG...LIMITING THE
CHANCES OF SEVERE WEATHER. STEERING FLOW SHOULD BE SUFFICIENT TO
KEEP CELLS MOVING ALONG. MAXIMUM TEMPERATURES WILL RUN NEAR NORMAL.

THE GA SHORTWAVE MOVES BY TO OUR S TONIGHT...WHILE ONLY MODEST
ELEVATED INSTABILITY REMAINS. MODEL SOUNDINGS SHOW DRYING THROUGH
THE COLUMN...PARTICULARLY ABOVE 700 MB. STEERING FLOW WILL BECOME
WEAKER IN THE LOWER LEVELS...BUT PRECIPITATION SHOULD DECREASE IN
COVERAGE AND INTENSITY. MINIMUM TEMPERATURES WILL RUN NEAR NORMAL.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUESDAY...A LARGE UPPER RIDGE WILL BUILD OVER THE
SOUTHEAST AND LWR-MID MS VALLEY WEDNESDAY AND THURSDAY.
MEANWHILE...A CLOSED UPPER LOW WILL DRIFT SOUTHEAST AND OPEN INTO A
DEEPER TROF ALONG THE EAST COAST. THIS WILL PLACE THE CWFA WITHIN
INCREASING NWLY MID-UPR FLOW. MODELS DISAGREE ON INDIVIDUAL EMBEDDED
SHORTWAVES RIDING OVER THE TOP OF THE BUILDING RIDGE AND DIVING
SOUTHEAST ACRS THE OH VALLEY TO THE MID ATLANTIC. IN ANY
CASE...EXPECT ABOVE NORMAL TEMPS BOTH DAYS...WITH PLENTY OF
INSTABILITY FOR AT LEAST SCATTERED MTN CONVECTION AND ISOLD ACRS THE
PIEDMONT. THERE IS SOME CONCERN THAT THE FLOW WILL PLACE THE AREA
WITHIN A FAVORED MCS TRACK. HOWEVER...CONFIDENCE IS STILL LOW...SUCH
THAT I DID NOT TRY TO ADJUST POPS BASED ON THAT (THE HIGHEST POPS
ARE ALREADY ALONG THE TN/NC BORDER BOTH DAYS). WITH THAT SAID...IF A
DECENT CLUSTER OF STORMS DEVELOPS TO OUR NW...THERE MAY BE ENUF
SHEAR TO ALLOW STRONG TO SEVERE STORMS AT LEAST REACHING THE
MTNS...IF NOT CROSSING THEM. THE NEW DAYS 2 AND 3 OUTLOOKS...HAVE A
MENTION OF POSSIBLE ORGANIZED CONVECTION ACRS THE MID MS AND OH
VALLEYS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 315 AM TUESDAY...THE 00Z MODEL SUITE (EXCEPT FOR THE
CMC)...HAVE TRENDED TO THE EAST WITH THE UPPER RIDGE AXIS...KEEPING
HIGHER HEIGHTS OVER THE CWFA THIS WEEKEND INTO EARLY NEXT WEEK. THIS
ACTUALLY RESULTS IN EVEN MORE PRONOUNCED BACKDOOR COLD FRONT AND
ENSUING WEDGE.

I BLENDED IN THE 00Z WPC GUIDANCE (THE SUPERBLEND GRIDS) FOR THE
DAYS 4 THRU 7. FRIDAY LOOKS TO STILL BE ABOVE NORMAL WITH DIURNAL
ISOLD TO SCATTERED CONVECTION. THE BACKDOOR COLD FRONT PUSHES IN
FRIDAY AFTN/EVE...WHICH COOLS THE NW NC PIEDMONT SLIGHTLY. THEN
SATURDAY AND SUNDAY...TEMPS RETURN TO NORMAL OR EVEN SLIGHTLY BELOW
NORMAL IN SPOTS...WITH INCREASED CLOUD COVER AND LIGHT E/NELY SFC
FLOW. POPS RAMP UP TO MORE WIDESPREAD CHC OVER THE WEEKEND. THEN THE
GFS AND ECMWF DIVERGE ON WHETHER WE DRY OUT ON MONDAY...WITH THE GFS
SHOWING THE WEDGE ENDING...WITH MUCH WARMER TEMPS. I HAVE LOWER POPS
AND SLIGHTLY WARMER TEMPS FOR MONDAY.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
AT KCLT...THE DEW POINT DEPRESSION IS RATHER LARGE AT THIS TIME...
AND A MODEL BLEND YIELDS ONLY LOW VFR VSBY BY DAYBREAK...WHICH MAY
BE TOO PESSIMISTIC. LOW VFR CLOUDS ARE NOT EXPECTED TO BECOME
PREVALENT UNTIL MORNING...AS A MID LEVEL SYSTEM MOVES ACROSS SC. THE
LOW VFR CIG WILL THEN ERODE AFTER SUNSET AS THE MID LEVEL SYSTEM
DEPARTS. CONVECTIVE CHANCES LOOK BEST AT PEAK HEATING IN THE
AFTERNOON. LIGHT SW WINDS ARE EXPECTED TO VEER NW BY MID DAY.

ELSEWHERE...DEW POINT DEPRESSION ARE NOT VERY SUPPORTIVE OF FOG AT
KGSP AND KGMU...BUT GUIDANCE DOES TAKE KHKY DOWN TO MVFR VSBY BY
DAYBREAK. GUIDANCE SUGGESTED IFR VSBY AT KAVL BY DAWN...BUT FOR SO
BRIEF A PERIOD THAT ONLY MVFR WILL BE CARRIED THERE. KAND IS
EXPECTED TO HAVE MVFR FOG AS WELL. VFR RETURNS BY MID MORNING. LOW
VFR CIGS WILL DEVELOP IN THE MOUNTAINS AS A MID LEVEL SYSTEM
APPROACHES FROM THE WEST TOWARD DAWN...WITH GUIDANCE SUPPORTING
BRIEF MVFR AT KAVL AROUND DAYBREAK. THE LOW VFR CIGS WILL SET UP IN
THE FOOTHILLS AFTER DAYBREAK. CONVECTIVE CHANCES WILL BE BEST WITH
AFTERNOON HEATING...BUT SOME PRECIPITATION MAY CROSS THE SAVANNAH
RIVER AND AFFECT SC SITES AROUND DAYBREAK. LOW VFR CIGS WILL ERODE
THIS EVENING AS THE MID LEVEL SYSTEM DEPARTS.SW WINDS WILL VEER TO W
IN THE FOOTHILLS THIS AFTERNOON. WINDS WILL REMAIN CHANNELED UP
VALLEY FORM THE NW AT KAVL.

OUTLOOK...SCT AFTERNOON CONVECTION AND PATCHY EARLY MORNING FOG WILL
REMAIN IN THE FORECAST THROUGH THE WEEK. THERE WILL ALSO BE
INCREASING CHANCES FOR ORGANIZED CONVECTION APPROACHING THE AREA
FROM THE NW DURING THE LATE NIGHT/EARLY MORNING HOURS.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-08Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH  87%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   77%     HIGH  99%     HIGH 100%     HIGH 100%
KHKY       HIGH  93%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  96%     HIGH  93%     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...ARK
NEAR TERM...JAT
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...JAT






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