Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 120515
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
115 AM EDT SAT JUL 12 2014

.SYNOPSIS...
WEAK HIGH PRESSURE IN CONTROL OF OUR WEATHER THIS WEEKEND. AN
UNSEASONABLY STRONG COLD FRONT IS THEN EXPECTED TO REACH THE WESTERN
CAROLINAS BY TUESDAY INCREASING THE POSSIBILITY OF WIDESPREAD
THUNDERSTORMS. EXPECT COOLER THAN NORMAL TEMPERATURES FOR MUCH OF
THE LAST HALF OF THE WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...POPS AND QPF HAVE BEEN INCREASED IN NE GA AND FAR
NW SC PER RADAR TRENDS. WINDS WERE UPDATED WITH A BLEND OF THE
LATEST NAM AND ADJMAV. AREAS OF FOG WERE UPDATED FORM THE LATEST
MODEL GUIDANCE. SKY COVER WAS UPDATED FROM INFRARED SATELLITE
IMAGERY.

AS OF 1010 PM...AN INTERESTING CONVECTIVE CLUSTER HAS REMAINED
ACROSS NE GA...JUST WEST OF THE FORECAST AREA...FOR SEVERAL HOURS
THIS EVENING. LATEST RADAR IMAGES INDICATE THAT A CONVEYOR BELT OF
FEEDER CELL HAVE DEVELOP ACROSS THE UPPER SAVANNAH RIVER
VALLEY...TRACKING INTO THE NEARLY STATIONARY STORM CLUSTER. AREA OF
50 DBZ AND LIGHTNING TRENDS ARE DOWN OVER THE PAST HALF HOUR. I WILL
ANTICIPATE THAT THE CLUSTER WILL STEADILY WEAKEN AND DISSIPATE SHORT
AFTER THE LATEST ROUNDS OF FEEDER CELLS MERGE. TO THE NORTH...SKC
REMAINS CLEAR WITH CALM WIND. I WILL UPDATE THE POPS TO ADJUST POPS
AND TIMING ACCORDING TO LATEST THINKING. UPDATE HWO WILL BE ISSUED
SOON.

AS OF 745 PM...CU HAS BECOME LIMITED TO EXTREME NE GA AND THE NC
MTNS. RADAR IMAGE INDICATE A CLUSTER OF OUTFLOW ASSOCIATED SHRA/TSRA
ACROSS NRN GA. THESE CELLS ARE SLOW MOVING AND WOULD LIKELY
ENCOUNTER MORE LLVL INHIBITION BY THE TIME ANY BOUNDARY REACHES THE
WESTERN EDGE OF THE CWA. THE COMBINATION OF WEAK FLOW AND DIURNAL
DECREASE OF INSTABILITY...I WILL KEEP SCHC TO CHC POPS AROUND AREA
OF CURRENT ACTIVITY FOR THE NEXT 1-3 HOURS...THEN DROP MENTION OF
CONVECTION. I WILL UPDATE THE FORECAST TO INCREASE MENTION OF FOG
WITHIN THE MTN VALLEYS.

AS OF 525 PM...LATEST SATELLITE IMAGES CONTINUE TO INDICATE
ENHANCED CU ACROSS THE MTNS AND ADJACENT FOOTHILLS. THE CU ALONG AND
EAST OF I-85 AND I-77 APPEARED TO BE SMALL CELLS WITH SHALLOW
VERTICAL DEVELOPMENT. KGSP RADAR INDICATED A FEW SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS THE EAST FACING SLOPES...THE GREATEST
COVERAGE WAS NEAR THE NC/GA/SC STATE LINE INTERSECTION. I WILL
UPDATE THE FORECAST TO ADJUST POPS AND ALIGN TEMPERATURES TO
OBSERVATIONS.

AS OF 230 PM EDT FRIDAY...QUASI STATIONARY SURFACE FRONTAL BOUNDARY
REMAINS IN PLACE ACROSS THE MIDLANDS OF SC..EASTWARD INTO THE
SANDHILLS AND COASTAL PLAINS OF NC.  DESPITE THE WEAK FROPA...NOT
MUCH HAS CHANGED THERMODYNAMICALLY ACROSS THE CWFA TODAY.  DEWPOINTS
REMAIN IN THE UPPER 60S TO LOWER 70S WITH MODEST HEATING ALLOWING
FOR CONDITIONAL DESTABILIZATION.  UPPER RIDGE BUILDING IN OVER THE
SOUTHERN PLAINS CONTINUES TO STRETCH EASTWARD ALLOWING FOR HEIGHTS
TO RISE OVER THE SOUTHEAST.  THUS...FORECAST SOUNDINGS INDICATE
IMPROVING MID LEVEL SUBSIDENCE LEADING TO A PARTIALLY CAPPED
ENVIRONMENT.  KEPT POPS AT SOLID CHANCE LEVELS ACROSS THE BLUE RIDGE
THIS AFTERNOON TAPERING TO NO MENTIONABLE POPS EASTWARD INTO THE
NC/SC PIEDMONT REGIONS WHERE CAPPING SHOULD HOLD.  NOT EXPECTING ANY
OF THE MTN SHOWERS/THUNDERSTORMS TO DEVELOP ANY DEEP UPDRAFTS WHICH
WILL LIMIT LONGEVITY AND INTENSITY.  THAT SAID...ABUNDANT DCAPE IN
THE REGION COULD YIELD A MODEST MICROBURST THREAT ALONG WITH
FREQUENT CLOUD TO GROUND LIGHTNING WITH THE STRONGER CELLS.

THINGS WILL QUIET DOWN OVERNIGHT AS HEATING IS LOST AND WEAK UPSLOPE
FLOW SUBSIDES.  GUIDANCE INDICATES THE MOIST BOUNDARY LAYER WILL
DECOUPLE ALLOWING FOR LOW STRATUS AND/OR FOG TO DEVELOP IN AND
AROUND THE MOUNTAIN VALLEYS...AND POTENTIALLY TO A LESSER DEGREE
ACROSS THE NC PIEDMONT.  TYPICAL SUMMERTIME PATTERN RETURNS ON
SATURDAY AS HIGH PRESSURE ACROSS THE NORTHEAST GIVES WAY TO THE
BERMUDA HIGH.  IN RESPONSE...STRONG SOUTHEASTERLY FLOW WILL RETURN
LEADING TO A DIURNAL POP/TEMPERATURE TREND.  FORECAST WILL FEATURE
CHANCES POPS IN THE CLIMO FAVORED REGIONS OF THE HIGH TERRAIN WHERE
UPSLOPE ENHANCEMENT OCCURS...ALONG WITH SLIGHT CHANCE POPS ALONG THE
SOUTHERN TIER OF THE CWFA WHERE SURFACE CONVERGENCE ALONG OLD
STATIONARY FRONT COULD INITIATE SHOWERS/THUNDERSTORMS AS ABOVE
MENTIONED SOUTHEASTERLY FLOW MIGRATES THE FRONT NORTH.  TEMPERATURES
THROUGH THE PERIOD WILL REMAIN AT OR JUST ABOVE NORMAL LEVELS.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
AS OF 145 PM FRI...LATEST GUIDANCE STILL SUGGESTS THAT THE SHORT
TERM WILL FEATURE RATHER TYPICAL JULY WEATHER FOR THE WESTERN
CAROLINAS AND NE GA. HIGH PRESSURE WILL REMAIN RIDGED OVER THE AREA
SATURDAY THROUGH SUNDAY AS A WESTWARD EXTENSION OF THE BERMUDA HIGH.
THE HIGH WILL BEGIN TO BREAK DOWN OVER THE AREA ON MONDAY AS HEIGHTS
BEGIN TO FALL ACROSS THE EASTERN U.S. IN RESPONSE TO A STRONG UPPER
LOW DROPPING SOUTHEAST OUT OF CANADA TOWARD THE GREAT LAKES.
HENCE...A MORE PROMINENT LEE TROUGH IS SHOWING UP IN THE MODEL
GUIDANCE FOR MONDAY...WHICH SHOULD SERVE AS A TRIGGER FOR MORE
CONVECTION OVER THE PIEDMONT THAN ON PREVIOUS DAYS. TO
SUMMARIZE...ON SUNDAY AFTERNOON CONVECTION SHOULD BE MOSTLY CONFINED
TO THE UPSLOPE AREAS IN THE MOUNTAINS...WHILE ON MONDAY ALL AREAS
SHOULD SEE SCATTERED CONVECTION DURING THE AFTERNOON. MAX TEMPS
SUNDAY AND MONDAY WILL BE AT OR A DEGREE OR TWO ABOVE CLIMO NORMALS.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 200 PM FRI...ONE THING THAT THE MEDIUM RANGE GUIDANCE
CONTINUES TO AGREE UPON IS THE DISTINCT UPPER LEVEL PATTERN CHANGE
THAT IS FORECAST TO OCCUR IN THE EARLY TO MID WEEK PERIOD ACROSS THE
EASTERN PART OF THE NATION. A DEEP UPPER LOW IS STILL FORECAST TO
SWING SOUTH OUT OF NORTHERN CANADA AND ESTABLISH AN ANOMALOUS UPPER
TROUGH OVER THE EAST BY MIDWEEK. HOWEVER...THE DETAILS ARE BECOMING
A LITTLE MORE MURKY IN OUR REGION AS THE 12Z GFS HAS GONE OUT ON ITS
OWN IN REGARD TO FRONTAL TIMING, POSITION AND FRONTAL WAVE
DEVELOPMENT. THE 12Z GFS IS FASTER THAN ITS PREVIOUS RUNS AND WITH
THE CMC/ECF IN MOVING THE UPPER LOW INTO THE GREAT LAKES...AND IT
DOES NOT MOVE THE LOW AS FAR SOUTH. IN FACT...IT KEEPS THE UPPER LOW
CENTER ACROSS THE NORTHERN LAKES. THIS OF COURSE ULTIMATELY AFFECTS
HOW FAR SOUTH THE SURFACE COLD FRONT CAN BE DRIVEN. THE 12Z GFS
MOVES THE COLD FRONT INTO THE NC MOUNTAINS MONDAY NIGHT...THEN
STALLS THE BOUNDARY SOMEWHERE ACROSS THE PIEDMONT ON TUE. THEN IT
DEVELOPS A SERIES OF FRONTAL WAVES TUE-THU WITH WIDESPREAD PRECIP
EACH DAY. WPC ON THE OTHER HAND HAS GONE WITH A MORE EC/CMC SOLUTION
WHICH BRINGS THE FRONT INTO THE AREA ON TUE AND MOVES THE FRONT FAR
ENOUGH SOUTH OF THE AREA TO ALLOW DRIER AIR TO WORK INTO THE REGION
WED INTO THU. ALTHOUGH THE 00Z GFS ENSEMBLE IS ALSO FARTHER NORTH
WITH THE FRONTAL BOUNDARY...IT IS NOT AS FAR NORTH AS THE 12Z
OPERATIONAL POSTIION. AT THIS JUNCTURE...WE PREFER TO TREND
TOWARD THE WPC SOLUTION WHICH IS MORE CONSISTENT WITH PREVIOUS
FORECASTS. WE WILL LINGER SOME POPS OVER MOST OF THE AREA ON WED DUE
TO THE UNCERTAINTY INVOLVED...BUT WILL ALLOW FOR A DRY DAY ON THU.
WILL PROBALBY FEATURE CLIMO POPS ON FRI AS THE FRONT MAY BEGIN TO
RETURN NORTHWARD.

IN REGARD TO IMPACTS...THE FRONT WILL BE WELL FORCED FOR JULY AND
CAPES COULD POOL AHEAD OF THE FRONT TO PERHAPS 1500-2000J/KG
DEPENDING ON TIMING...SO THERE IS A POSSIBILITY FOR AN ORGANIZED
SEVERE STORM EVENT WITH THE FRONTAL PASSAGE. WIND SHEAR WILL BE
RATHER GOOD FOR JULY WITH FORECAST SOUNDINGS FEATURING UP TO 30-40KT
OF 0-6KM BULK SHEAR. ALSO...TEMPS ARE STILL EXPECTED TO BE AT LEAST 2
STANDARD DEVIATIONS BELOW AVERAGE WED AND THU. FOR INSTANCE...THE
12Z CONSRAW GUIDANCE FOR WED HAS MAX TEMPS CLOSE TO 10 DEGREES BELOW
CLIMO.

TO SUMMARIZE...A STRONG COLD FRONT IS FORECAST TO ARRIVE ON TUESDAY
BRINGING THE POTENTIAL FOR SEVERE THUNDERSTORMS. MUCH  COOLER WEATHER
IS EXPECTED WED AND THU WITH A LINGERING CHANCE FOR SHOWERS ON WED.
THU MAY BE A DRY DAY...THEN A CHANCE FOR SHOWERS/STORMS WILL RETURN
FOR FRIDAY.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...MODEL GUIDANCE IS SUPPORTIVE OF AN MVFR FOG RESTRICTION
BEFORE DAWN. ALTHOUGH MODEL TIME HEIGHTS SHOW VERY LOW LEVEL
MOISTURE...CONFIDENCE ON SUFFICIENT CLOUD COVER FOR A CIG IS
LOW....SO ONLY SCATTERED LOW CLOUDS WILL BE CARRIED AT DAWN. VFR
RETURNS BY MID MORNING...WITH LIGHT SE WINDS PERSISTING. WINDS VEER
SOUTH THIS EVENING. CONVECTIVE CHANCES ARE QUITE LOW TODAY AS A MID
LEVEL WARM NOSE IS EXPECTED TO LIMIT LIFT.

ELSEWHERE...GUIDANCE SUPPORTS MVFR VSBY IN FOG BY DAYBREAK AT SC
SITES...IFR AT KHKY...AND LIFR TO VLIFR IN MOUNTAIN VALLEYS...
INCLUDING KAVL. CIG RESTRICITONS APPEAR MOST LIKELY IN MOUNTAIN
VALLEYS...WHERE IFR WILL BE CARRIED. CONFIDENCE IS LIMITED FOR LOW
CLOUDS IN THE FOOTHILLS...GIVEN CURRENT OBSERVATIONS. WITH GUIDANCE
SHOWING MOIST LOW LEVELS...SCATTERED LOW CLOUDS WILL BE CARRIED AT
DAYBREAK AT KGSP AND KGMU...WITH MVFR AT KAND WHERE A CIG EXISTS
ALREADY. CONVECTIVE CHANCES WILL BE BEST IN THE MOUNTAINS...BUT TOO
LOW TO MENTION AT KAVL.

OUTLOOK...HIGH PRESSURE WILL SLOWLY SETTLE OVER THE AREA THIS
WEEKEND. ANY RESTRICTIONS SHOULD MAINLY BE CONFINED TO DIURNAL TSTMS
AND MORNING VALLEY FOG EACH DAY.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-05Z
KCLT       HIGH  82%     HIGH  87%     HIGH 100%     HIGH 100%
KGSP       HIGH  85%     HIGH  88%     HIGH 100%     HIGH 100%
KAVL       LOW   59%     MED   61%     HIGH  92%     HIGH 100%
KHKY       HIGH  85%     HIGH  84%     HIGH 100%     HIGH 100%
KGMU       HIGH  82%     HIGH  86%     HIGH 100%     HIGH 100%
KAND       HIGH  81%     HIGH  87%     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...CDG/JAT/NED
SHORT TERM...LG
LONG TERM...LG
AVIATION...JAT





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