Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 191755
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
155 PM 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/...
AS OF 145 PM...SCATTERED CONVECTION IS DEVELOPING ALONG A NARROW
AXIS FROM THE SOUTHERN NC FOOTHILLS...ACROSS THE SOUTHWEST NC
PIEDMONT AND NORTHERN TIER OF COUNTIES IN SC...GENERALLY ALONG A
WEAK CONVERGENT/INSTABILITY AXIS. MUCH BETTER COVERAGE EXISTS FROM
UNION COUNTY NC SOUTH INTO THE SC MIDLANDS...LIKELY SUPPORTED BY A
SHORT WAVE TROUGH THAT SHOWS SUBTLY ON THE LATEST WV IMAGERY.
ADDITIONAL CONVECTION WAS DEVELOPING ACROSS THE GREAT TENN VALLEY...
WHICH WILL APPROACH THE WESTERN NC MTNS THROUGH THE AFTERNOON...
SUPPORTED BY A WEAK NW/UPSLOPE FLOW. POPS WILL GENERALLY REMAIN IN
THE 30 TO 40 PERCENT RANGE THROUGH THE AFTERNOON...BUT WILL LIKELY
NEED SOME REFINEMENT SHORTLY DEPENDING UPON RADAR TRENDS. MOIST
PROFILES/HIGH FREEZING LEVELS SHOULD RESULT IN A MINIMAL SEVERE
WEATHER THREAT. BUT WHILE MEAN CLOUD-BEARING FLOW SHOULD SUPPORT
10-20 KT CELL MOVEMENT TOWARD THE SE...SOME SUBTLE BACK-BUILDING HAS
BEEN OBSERVED IN SPOTS...SO THE MAIN THREAT MAY BE LIMITED TO A LOW
END/LOCALIZED FLASH FLOOD CONCERN.

AS OF 1050 AM...SCATTERED SHOWER ACTIVITY ASSOCIATED WITH WEAK
MID-LEVEL SHORT WAVE TROUGH IS IN THE PROCESS OF DISSIPATING ACROSS
THE SC PIEDMONT THIS MORNING. ADDITIONAL SHOWER ACTIVITY IS
PROGRESSING ACROSS CENTRAL GEORGIA ATTM...WITH A TRAJECTORY THAT
WOULD CARRY IT INTO THE SC MIDLANDS THIS AFTERNOON. THE UPSHOT IS
FAIRLY QUIET WEATHER IS ANTICIPATED ACROSS THE AREA OVER THE NEXT
2-4 HOURS. THIS WILL HOWEVER ALLOW FOR SOME DECENT INSOLATION OVER
THE AREA (DESPITE PARTLY/MOSTLY CLOUDY SKIES ASSOCIATED WITH
MID-LEVEL MOISTURE)...WHICH WILL RESULT IN SOME DESTABILIZATION THIS
AFTERNOON. MORNING SOUNDINGS INDICATE LAPSE RATES TENDING STRONGLY
TOWARD MOIST ADIABATIC THROUGH A DEEP LAYER...SUGGESTING ANY
INSTABILITY WILL BE QUITE MODEST...ALTHOUGH PWATS ARE A LITTLE ABOVE
CLIMO. EXPECT SCATTERED DEEP CONVECTION TO DEVELOP OVER THE HIGH
TERRAIN...ESP NEAR THE BLUE RIDGE THIS AFTERNOON...THEN MOVE E/SE.
OVERALL...DECIDED NOT TO ARGUE WITH THE CURRENT 30-40 POPS BEING
ADVERTISED...BUT WOULD NOT BE SURPRISED IF THIS TURNS OUT TO BE A
TAD HIGH...ESP SINCE WE ARE GOING TO SEE AN INCREASE IN LARGE SCALE
WEAK SUBSIDENCE IN THE WAKE OF THE PARTING SHORT WAVE. TEMPS SHOULD
WARM TO WITHIN A DEGREE OR SO OF CLIMO.

1130 UTC UPDATE...POPS AND QPF HAVE BEEN INCREASED IN THE SW
MOUNTAINS AND UPPER UPPER SAVANNA ROVER VALLEY EARLY ON PER RADAR
TRENDS. SKY COVER WAS UPDATED FROM INFRARED SATELLITE IMAGERY...
RESULTING IN A DECREASE IN CLOUD COVER IN THE EAST. WINDS WERE
UPDATED TO INCORPORATE THE 06Z NAM. AREAS OF FOG WERE UPDATED FROM
OBSERVATIONS.

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 /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT AND ELSEWHERE...SCATTERED CONVECTION IS DEVELOPING GENERALLY
ALONG/EAST OF A LINE FROM KAVL TO KGSP...AND SOUTH OF A LINE FROM
KAVL TO KHKY. AS SUCH...THE MOST LIKELY TERMINALS TO SEE CONVECTION
IN THE VERY NEAR TERM WILL BE KCLT AND KGSP...MAINLY AFTER 19Z.
ALTHOUGH THERE HAVE BEEN OCCL LIGHTNING STRIKES WITH THIS
ACTIVITY...BASED UPON THE MAGNITUDE OF INSTABILITY...FEEL THAT
COVERAGE OF TS IS SUCH THAT TEMPOS CAN BE LIMITED TO -SHRA AT THESE
TWO TERMINALS (ALONG WITH VCTS AT KGSP)...WHILE THE MENTION WILL BE
LIMITED TO VCTS/VCSH ELSEWHERE. CONVECTION SHOULD DIMINISH TO
ISOLATED COVERAGE OR LESS THIS EVENING. THE MAIN CONCERN THEN WILL
SHIFT TO THE LATE NIGHT/EARLY MORNING FOG DEVELOPMENT. MVFR BR HAS
BEEN INCLUDED AT MOST TERMINALS PRIOR TO 12Z. WHILE KAVL STANDS A
REASONABLE CHANCE TO SEE IFR OR LOWER CONDITIONS...CONFIDENCE IS
RATHER LOW ATTM.

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

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH  92%     HIGH 100%     HIGH  91%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH  95%     HIGH 100%
KAVL       HIGH  85%     HIGH  95%     HIGH 100%     HIGH  98%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH  95%     HIGH  95%

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/JDL
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...JDL





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