Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 140606
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
206 AM EDT SUN SEP 14 2014

.SYNOPSIS...
A STATIONARY FRONT WILL REMAIN JUST TO OUR SOUTH 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 TODAY/...
130 AM UPDATE...CONVECTION REALLY WOUND DOWN BY MIDNIGHT THOUGH A
FEW VERY LIGHT SHOWERS ARE SEEN OVER THE NC PIEDMONT ATTM. WEDGE
FRONT APPEARS TO BE ACRS THE I-20 CORRIDOR AS DELINEATED BY WINDS
AND DEWPOINTS. GENERALLY EXPECTING A QUIET NIGHT TO
CONTINUE...THOUGH THERE IS WEAK UPGLIDE ONGOING OVER THE WEDGE WHICH
IS SHOWN TO INCREASE BEFORE SUNRISE. MODELS DO NOT RESPOND WITH MUCH
QPF BUT I DID RETAIN AN INCREASE IN POPS THRU THE MRNG...WITH
UPGLIDE WEAKENING AS DIURNAL HEATING GETS UNDERWAY ALONG THE
PERIPHERY OF THE WEDGE. THE NAM/GFS AND MESO MODELS DEVELOP SOME
LIGHT QPF OVER THE CENT/SRN MTNS AND MUCH OF THE SC/GA ZONES
EVIDENTLY FOR THIS REASON. REVISED POP TRENDS THRU 12Z MON ARE
PRETTY SIMILAR TO BEFORE.

PREVIOUS DISCUSSION...COOL HIGH PRESSURE WEDGING DOWN THE EAST
SLOPES OF THE APPALACHIANS WILL CONTINUE 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 REACH. IT WILL BE A COOL DAY ON
SUNDAY WITH MAX TEMPS UP TO 15 DEGREES SHY OF CLIMO OUTSIDE THE
MOUNTAINS.

&&

.SHORT TERM /TONIGHT 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 /06Z SUNDAY THROUGH THURSDAY/...
AT KCLT...STRONGEST SIGNAL FROM GUIDANCE REMAINS FOR CIGS TO BOTTOM
OUT AT MVFR EARLY THIS MRNG...IN WARM UPGLIDE REGIME ATOP A COOL
WEDGE OF HIGH PRESSURE. NELY WINDS ARE EXPECTED TO STAY UP ENOUGH TO
KEEP THE BDY LAYER MIXED AND FOG FREE. MVFR CIG CONTINUES UNTIL THEY
LIFT TO VFR MIDDAY. PRECIP CHANCES ARE TOO LOW TO MENTION THIS
MRNG...BUT THE WEDGE FRONT WILL BE NOT TOO FAR S OF THE FIELD DURING
THE DAY TODAY AMD IS PROGGED TO FOCUS CONVECTIVE DEVELOPMENT...
ALBEIT MINOR IN IMPACT DUE TO POOR LAPSE RATES. HAVE INCLUDED A
PROB30 FOR LOW CHANCE OF A PASSING SHOWER. NE WINDS CONTINUE UNTIL
GOING CALM AFTER SUNSET.

ELSEWHERE...CIGS ARE THE MAIN CONCERN THIS MRNG WITH HIGH PRESSURE
WEDGE ALLOWING WARM UPGLIDE AND ASSOCIATED CLOUD COVER. HOWEVER THEY
ARE EXPECTED TO BE NO LOWER THAN MVFR AS N TO NE BREEZES
PERSIST...KEEPING SFC CONDITIONS MIXED. KAND IS AN EXCEPTION AS THE
SITE SAW INTENSE RAINFALL SATURDAY AFTN AND IS NEARER THE WEDGE
BOUNDARY...THUS PROGGED TO GO IFR AT DAYBREAK. PRECIP CHANCES ARE
LOW ENOUGH TO MENTION AS VCSH IF AT ALL TODAY...WITH MOST GUIDANCE
SHOWING THE ONGOING WARM UPGLIDE PRODUCING LITTLE PRECIP...AND
INSTEAD SHOWING WEAK CONVECTIVE CELLS DEVELOPING NEAR THE WEDGE
BOUNDARY. HENCE NO MENTION AT KHKY. WINDS REMAIN NE...EXCEPT AT KAVL
WHICH SHOULD SEE CHANNELED SE FLOW DURING THE AFTN. MOST AREAS
SHOULD GO CALM THIS EVENING.

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...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  86%     MED   72%     HIGH  87%     HIGH  84%
KGSP       MED   79%     HIGH  96%     HIGH  83%     HIGH  82%
KAVL       HIGH  87%     HIGH  89%     HIGH  87%     HIGH  81%
KHKY       HIGH  94%     HIGH  83%     HIGH  87%     HIGH  89%
KGMU       MED   79%     HIGH  95%     HIGH  83%     HIGH  82%
KAND       HIGH  92%     HIGH  87%     HIGH  88%     MED   78%

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





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