Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 132027
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
427 PM EDT SAT SEP 13 2014

.SYNOPSIS...
A STATIONARY FRONT WILL REMAIN JUST TO OUR SOUTH OVER THE WEEKEND
AND INTO EARLY NEXT WEEK WITH HUMID AND UNSETTLED WEATHER EACH DAY.
A BACK DOOR COLD FRONT WILL THEN CROSS THE AREA BY THE MIDDLE OF
NEXT WEEK WITH A COOL AIR WEDGE PATTERN SETTING UP BY THE END OF THE
WORK WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
2030 UTC UPDATE...POPS AND QPF WERE REALIGNED BASED ON RADAR
TRENDS...FAVORING A SWATH FROM RUTHERFORD COUNTY NC...TO SPARTANBURG
AND PICKENS COUNTIES IN SC...AS WELL AS ELBERT AND FRANKLIN COUNTIES
IN GA. SKY COVER WAS UPDATED FROM SATELLITE IMAGERY...ACCOUNTING FOR
BREAKS OVER WESTERN NC AND THE SC PIEDMONT.

AT 215 PM...LATEST SFC ANALYSIS SHOWS COLD FRONT FROM JUST NW OF
CLT...SW THROUGH THE NORTHERN UPSTATE OF SC INTO NE GA. RADAR IS
BEGINNING TO LIGHT UP ALONG THE BOUNDARY OVER THE WESTERN UPSTATE
INTO NE GA. EXPECT THIS TREND TO CONTINUE AS THE FRONT SAGS SLOWLY
SE THROUGH THE AFTERNOON. WITH CAPES IN THE 2000-3000J/KG RANGE OVER
THE SOUTHERN UPSTATE AND PRECIP WATER AROUND 2 INCHES THERE SHOULD
BE SOME STRONG THUNDERSTORMS LATE THIS AFTERNOON. HOWEVER...THE MAIN
THREAT WILL BE LOCALLY HEAVY RAIN AND PERHAPS SOME LOCALIZED FLASH
FLOODING. HENCE....THE NUMEROUS COVERAGE TYPE POPS LOOK GOOD ACROSS
THE PIEDMONT AREAS THIS AFTERNOON. LOOKS LIKE THE MOUNTAINS AND MOST
FOOTHILL LOCATIONS SHOULD REMAIN DRY FOR THE REMAINDER OF THIS
AFTERNOON. AS MENTIONED EARLIER...THE 12Z NAM KEEPS THE FRONT
QUASI-STATIONARY ACROSS THE SOUTHERN UPSTATE FOR A GOOD PORTION OF
THE NIGHT AND WORKS IT OVER WITH CONVECTION PRODUCING HEAVY RAIN ON
THE ORDER OF 4 INCHES. THE 12Z GFS IS MORE PROGRESSIVE WITH THE
FRONT WITH NO QPF BOMBS. HENCE...WILL TREND THE FORECAST TO A MORE
PROGRESSIVE FRONTAL BOUNDARY AND ONLY MODERATE QPF VALUES. THERE
COULD BE SOME LOCALLY HEAVY RAIN IN THE 2-4 INCH RANGE ACROSS THE
SOUTHERN UPSTATE...BUT NOT AS WIDESPREAD AS WHAT THE NAM SUGGESTS.
THEREFORE...NO FLASH FLOOD WATCH.

AS THE FRONT SETTLES SOUTH OF THE AREA AFTER MIDNIGHT...COOL HIGH
PRESSURE WILL BEGIN WEDGING DOWN THE EAST SLOPES OF THE APPALACHIANS
WITH CAD CONDITIONS CONTINUING THROUGH SUNDAY. LOOKS LIKE CLOUDS
WILL BE PLENTIFUL...BUT ISENTROPIC LIFT OVER THE WEDGE LOOKS WEAK...
SO PRECIP CHANCES ARE ON THE LOW END FOR SUNDAY. THE SW HALF OF THE
AREA STANDS THE BEST CHANCE FOR SOME PATCHY LIGHT RAIN...AND EVEN
SOME SCT SHOWERS/THUNDERSTORMS OVER THE SW MOUNTAINS WHERE THE WEDGE
AIRMASS TYPICALLY DOES NOT MAKE IT INTO. IT WILL BE A COOL DAY ON
SUNDAY WITH MAX TEMPS UP TO 15 DEGREES SHY OF CLIMO OUTSIDE THE
MOUNTAINS.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 210 PM SATURDAY...WE APPEAR TO HAVE ENTERED INTO A PERIOD OF
TIME WHEN COLD AIR DAMMING WEDGES WILL WAX AND WANE AS THE OVERALL
UPPER PATTERN REMAINS FAIRLY CONSTANT...WHILE AN OLD SURFACE
BOUNDARY REMAINS STRUNG OUT W TO E TO OUR SOUTH AND HIGH PRESSURE
CENTERS PASS BY TO OUR N. THE PROBLEM IS THAT EACH PASSING HIGH
STAYS PROGRESSIVE...SO THE WDEGE NEVER REALLY LOCKS IN. THE FIRST
SUCH WEDGE ON SUNDAY NIGHT WEAKENS AND FALLS APART ON MONDAY AS WHAT
PASSES FOR A PARENT HIGH DRIFTS OFF THE NE COAST AND WEAKENS FURTHER
AND A LEE TROF ESSENTIALLY OVERWHELMS THE REMNANT COOL POOL E OF THE
MTNS. AFTER MILD OVERNIGHT TEMPS...THIS SHOULD ALLOW FOR SOME
REBOUND OF HIGH TEMPS ON MONDAY ASSUMING THE COOL POOL DRAINS AND WE
GET SOME AFTERNOON SUN ACROSS THE FOOTHILLS AND PIEDMONT. HAVE
CONTINUED A DOWNWARD TREND ON PRECIP CHANCES BASED ON THE NEW MODEL
GUIDANCE AND 09Z SREF.

ON MONDAY NIGHT...A FAIRLY STRONG SHORT WAVE WILL MOVE OVERHEAD
WHICH WILL SERVE TO BRING THE AXIS OF A BROAD UPPER TROF OVER THE
CAROLINAS FOR TUESDAY. THE APPROACH AND PASSAGE OF THIS WAVE MAY
TRIGGER ADDITIONAL SHOWER ACTIVITY OVERNIGHT SO A CHANCE POP WAS
KEPT ACROSS MOST OF THE REGION THROUGH TUESDAY MORNING. THIS FEATURE
WILL ALSO BRING A REINFORCING SURFACE BOUNDARY IN FROM THE WEST
WHICH SHOULD PUSH THROUGH EARLY IN THE DAY. BEHIND THIS
BOUNDARY...THE NEXT SURFACE HIGH SHOULD BRIDGE ACROSS THE
APPALACHIANS ON TUESDAY SETTING UP THE POTENTIAL FOR THE DEVELOPMENT
OF ANOTHER WEDGE-LIKE SCENARIO BY THE END OF THE DAY. THE GFS IS
MOST AGGRESSIVE WITH DEVELOPING NEW PRECIP IN THE DEVELOPING
EASTERLY UPSLOPE IN THE AFTERNOON BUT EVEN THE NAM HAS SOME ACTIVITY
NEAR THE MTNS. WILL NUDGE THE FCST IN THE DIRECTION OF THE LOWER POP
SEEN IN THE NEW MOSGUIDE AND AWAY FROM THE MORE ROBUST SREF. TEMPS
COULD BE TRICKY AGAIN IF NEW PRECIP DEVELOPS PER THE GFS. EXPECT
TEMPS TO BE A BIT WARMER ACROSS THE SOUTH BUT KEPT THEM THE SAME
ACROSS THE NRN TIER.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 155 PM SATURDAY...THE MEDIUM RANGE FCST PICK UP AT 00Z ON
WEDNESDAY WITH A BROAD...LONGWAVE UPPER TROF OVER THE EASTERN CONUS
AND UPPER RIDGING OVER THE WEST. THE TROF IS EXPECTED TO AMPLIFY TO
SOME DEGREE OVER THE NEXT COUPLE OF DAYS AND THEN LIFT NE BY THE END
OF THE WORK WEEK. BY NEXT WEEKEND...THE UPPER RIDGE WILL BUILD
EASTWARD AND LIKELY BE IN PLACE OVER THE FCST AREA BY NEW DAY 7.

AT THE SFC...A NORTHERN PLAINS HIGH WILL DRIFT FARTHER EAST ON TUES
AND SHOULD BE CENTERED OVER THE GREAT LAKES BY THE START OF THE
MEDIUM RANGE AT 00Z WED. THE MODELS CONTINUE TO INDICATE THAT THIS
HIGH WILL BE ABSORBED BY A STRONGER CANADIAN HIGH BY LATE WED/EARLY
THURS. THE HIGH WILL THEN DRIFT OVER NORTHERN NEW ENGLAND OVER THE
NEXT DAY OR TWO AND REMAIN THERE THRU NEW DAY 7. AT THE SAME
TIME...BOTH THE GFS AND ECMWF TRY TO SPIN UP A SFC LOW JUST OFF THE
CAROLINA COAST WHICH ACTS TO ENHANCE/STRENGTHEN A COLD AIR WEDGE PUT
IN PLACE BY THE NEAR STATIONARY SFC HIGH TO THE NE. THE CONSENSUS
AMONG THE GFS...ECMWF...AND CMC MODELS IS GOOD WRT THIS WEDGE
PATTERN DEVELOPING BY NEXT WEEKEND SO OVERALL FCST CONFIDENCE IS
IMPROVING. THE PRECIP CHANCES WERE NOT CHANGED MUCH FOR WED WITH A
SLIGHT TO SOLID CHANCE OVER THE CWFA BY EARLY AFTERNOON...HOWEVER I
DID LOWER VALUES FOR THE REST OF THE MEDIUM RANGE TO ACCOUNT FOR THE
STRONGER WEDGE PATTERN. I ALSO REDUCED THE OVERALL QPF EXPECTED FOR
THE EARLY PART OF THE PERIOD. TEMPS WILL START OUT ABOUT A CATEGORY
BELOW NORMAL ON WED AND DROP A FEW MORE DEGREES BY THE WEEKEND. IF
CURRENT MODEL TRENDS CONTINUE AND THE WEDGE IS EXPECTED TO BE EVEN
STRONGER...TEMPS MAY NEED TO BE LOWERED MORE.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
AT KCLT...CIGS ON THERE WAY UP LIFTING TO LOW VFR. COLD FRONTAL
BOUNDARY IS MOVING SLOWLY SE AND WILL SLIP BY THE AIRFIELD BY 21Z.
IT WILL BE CLOSE AS TO WHETHER ANY TSRA WILL AFFECT THE AIRFIELD. IT
IS POSSIBLE THAT CONVECTIVE INITIATION WILL OCCUR JUST TO THE SOUTH.
HOWEVER...WILL CONTINUE WITH A COUPLE HOUR TEMPO FOR TSRA WITH THE
FRONTAL PASSAGE PER LOCAL WRF MODEL. VFR CIGS ARE THEN EXPECTED TO
LOWER TO MVFR AND POSSIBLY EVEN IFR NEAR 12Z SUN AS COOL/MOIST WEDGE
LOCKS IN.

ELSEWHERE...KAVL AND KHKY SHOULD AVOID FRONTAL CONVECTION TODAY AND
HAVE VFR CEILINGS UNTIL MVFR WEDGE CLOUDINESS DEVELOPS LATE TONIGHT.
THE SC AIRFIELDS ARE LIKELY TO SEE TEMPO TSRA WITH THE COLD FRONTAL
PASSAGE THIS AFTERNOON. OTHERWISE...VFR CEILINGS WILL LOWER TO LOW
MVFR LATE TONIGHT AS WEDGE CLOUDINESS DEVLOPS.

OUTLOOK...WEDGE WILL HANG ON INTO MONDAY MORNING ALONG WITH THE
ASSOCIATED MVFR/IFR CEILINGS. THE WEDGE SHOULD MIX OUT ON
MONDAY...BUT SCT SHOWERS/THUNDERSTORMS WILL DEVELOP AHEAD OF AN
APPROACHING COLD FRONT MONDAY AFTERNOON INTO MONDAY NIGHT. A RETURN
TO MAINLY VFR CONDITIONS IS EXPECTED TUE INTO MIDWEEK OUTSIDE OF
RESTRICTIONS WITH DIURNAL CONVECTION.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-20Z
KCLT       HIGH  87%     HIGH  99%     MED   78%     HIGH  95%
KGSP       HIGH  98%     HIGH  99%     MED   69%     HIGH  95%
KAVL       HIGH  91%     HIGH  85%     LOW   49%     HIGH  83%
KHKY       HIGH  94%     HIGH  94%     MED   76%     HIGH  87%
KGMU       HIGH  98%     HIGH  99%     HIGH  90%     HIGH  95%
KAND       HIGH  94%     HIGH  94%     MED   77%     HIGH  89%

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...JPT
NEAR TERM...JAT/LG
SHORT TERM...PM
LONG TERM...JPT
AVIATION...LG






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