Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS62 KGSP 132319
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
719 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/...
2315 UTC UPDATE...WINDS WERE UPDATED WITH A BLEND OF THE LATEST NAM
AND ADJMAV. POPS WERE UPDATED BASED ON SATELLITE IMAGERY...FAVORING
MAINLY THE SOUTHERNMOST PORTION OF THE AREA. QPF WAS ADJUSTED
ACCORDINGLY.

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 /23Z SATURDAY THROUGH THURSDAY/...
AT KCLT...GUIDANCE SUPPORTS AN MVFR CIG FORMING THIS EVENING...THEN
AN IFR CIG BEFORE DAWN...WITH MVFR VSBY IN FOG BY DAYBREAK...AS
MOISTURE PERSISTS IN THE LOW LEVELS. ALTHOUGH VSBY IMPROVES IN THE
MORNING...CIGS WILL ONLY SLOWLY;Y IMPROVE TO VFR BY MIDDAY. WINDS
WILL FAVOR THE NE. CONVECTIVE CHANCES REMAIN RATHER LIMITED IN
COOL HIGH PRESSURE TO THE NORTH OF A STATIONARY FRONT.

ELSEWHERE...CONVECTIVE CHANCES WILL DIMINISH FORM THE NORTH
OVERNIGHT AS COOL HIGH PRESSURE BUILDS IN FROM THE NORTH. GUIDANCE
FAVORS IFR TO LIFR VSBY IN FOG AT KAVL LATE TONIGHT...WITH MVFR AT
KGSP AND KAND...BUT LEAVES KHKY AND KGMU WITH VFR VSBY. CIG ON THE
OTHER HAND LOWER TO MVFR EVERYWHERE BY DAYBREAK...NOT RETURNING TO
MVFR UNTIL MIDDAY. CONVECTIVE CHANCES WILL IMPROVE FROM THE SOUTH ON
SUNDAY...MAINLY AFTER THIS TAF PACKAGE. WINDS WILL BE FROM THE
NE...EXCEPT AT KAVL...WHERE WINDS ARE EXPECTED TO VEER FROM NW
TONIGHT...TO SE ON SUNDAY.

OUTLOOK...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...

            23-05Z        05-11Z        11-17Z        17-23Z
KCLT       HIGH  92%     HIGH  94%     HIGH  86%     HIGH  80%
KGSP       HIGH  99%     HIGH  91%     HIGH  97%     MED   79%
KAVL       HIGH  96%     HIGH  84%     HIGH  94%     HIGH  82%
KHKY       HIGH 100%     HIGH  90%     HIGH  84%     HIGH  82%
KGMU       HIGH  97%     HIGH  93%     HIGH  95%     MED   76%
KAND       HIGH  96%     HIGH  81%     HIGH  93%     HIGH  81%

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...JAT






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.