Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 150550
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
150 AM EDT MON SEP 15 2014

.SYNOPSIS...
COOL BUT UNSETTLED WEATHER WILL CONTINUE THROUGH MONDAY NIGHT...AS A
STATIONARY FRONT WILL REMAIN JUST TO OUR SOUTH BEFORE AN UPPER
DISTURBANCE PASSES THROUGH. A COLD FRONT WILL THEN CROSS THE AREA IN
ITS WAKE...WHICH AGAIN STALLS TO OUR SOUTH. THIS WILL KEEP
TEMPERATURES A FEW DEGREES BELOW NORMAL INTO NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 145 AM MONDAY...SCT DEEP CONVECTION HAS DEVELOPED WITHIN THE
PAST COUPLE OF HOURS NEAR THE STALLED FRONTAL ZONE ALONG THE I-20
CORRIDOR. MOST OF THIS ACTIVITY SHOULD REMAIN COMFORTABLY SOUTH OF
OUR CWFA...BUT A SLIGHT CHANCE POPS IS PROBABLY WARRANTED ACROSS
MUCH OF OUR SOUTHERN AREAS THROUGH THE REMAINDER OF THE OVERNIGHT.
OTHERWISE...THE EARLY MORNING HOURS WILL BE MARKED BY ABUNDANT LOW
CLOUD COVER AND NEAR-NORMAL TEMPS IN LINGERING COLD AIR DAMMING
REGIME.

AT 1000 PM EDT SUNDAY...A BROAD LOW AMPLITUDE UPPER TROUGH EXTENDED
ACROSS THE NORTH CENTRAL PART OF THE NATION...WHILE A FLAT UPPER
RIDGE EXTENDED FROM TX TO THE GA COAST. A WEAK IMPULSE MOVING
THROUGH THE UPPER TROUGH WILL PASS TO THE NORTH OF NC OVERNIGHT.
SURFACE ANALYSIS PLACED A STATIONARY FROM THE GA COAST TO THE
NORTHERN GULF OF MEXICO. CONVECTIVE ACTIVITY WAS LOCATED ALONG THIS
BOUNDARY.

COOLER AIR NORTH OF THE FRONT EXTENDED ACROSS THE WESTERN CAROLINA
AND NE GA. ISOLATED SHOWERS MOVING NORTHEAST ALONG INTERSTATE 85
HAVE LARGELY ABATED THIS EVENING. WITH SOME WEAK ISENTROPIC UPGLIDE
REMAIN OVER OUR AREA...VERY SMALL POPS WILL REMAIN IN THE FORECAST
OVERNIGHT. MODEL GUIDANCE SUPPORTS FOG LATE TONIGHT...BUT ONLY HAD
SIGNIFICANT REDUCTIONS IN VISIBILITY IN THE MOUNTAINS. WITH LOW
CONFIDENCE IN DENSE FOG...NO ADVISORY WILL BE ISSUED AT THIS TIME.
MINIMUM TEMPERATURES WILL RUN SLIGHTLY ABOVE NORMAL DUE TO CLOUDS
AND LINGERING LOW LEVEL MOISTURE.

MONDAY...H85 WINDS WILL BECOME WEST DURING THE DAYLIGHT
HOURS...RESULTING IN DRYING ACROSS THE NC MTNS AND PIEDMONT.
HOWEVER...MOISTURE SHOULD REMAIN PLENTIFUL ACROSS THE SC AND GA
ZONES. THE COMBINATION OF DEEP MOISTURE AND WEAK INSTABILITY SHOULD
IN POPS RANGING FROM U40S ACROSS THE UPPER SAVANNAH RIVER VALLEY TO
SCHC ACROSS THE N I-77 CORRIDOR. THINNER CLOUD COVER AND WEAK
DOWNSLOPE WINDS SHOULD ALLOW TEMPERATURES TO REBOUND TO NEAR 80
ACROSS THE MTN VALLEYS...FOOTHILLS...AND PIEDMONT.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
AS OF 215 PM SUNDAY...THINK WE ARE ENTERING A PERIOD OF DIMINISHED
CONFIDENCE IN THE FORECAST FOR THE EARLY TO MIDDLE PART OF THE WEEK.
ASSUMING A REMNANT COOL POOL HAS BEEN ELIMINATED BY MONDAY EVENING
AND SOME CONVECTION HAS DEVELOPED...IT WILL PROBABLY LINGER WELL
INTO THE EVENING IN ADVANCE OF A SHORT WAVE. THIS WAVE WILL DRIVE A
REINFORCING SURFACE BOUNDARY ACROSS THE REGION LATE MONDAY NIGHT OR
EARLY TUESDAY MORNING...BUT ITS PASSAGE IS UNREMARKABLE IN THE MODEL
GUIDANCE. THE PRECIP CHANCE HAS A DOWNWARD TREND INTO TUESDAY
MORNING ONCE THAT BOUNDARY HAS MOVED PAST. IT IS FROM THAT POINT
ONWARD THAT CONFIDENCE IS RELATIVELY LOW. THE GFS ONCE AGAIN BRINGS
THE LOW LEVEL FLOW AROUND TO EASTERLY AND UPSLOPE BEHIND THE
BOUNDARY ON TUESDAY AFTERNOON...AND DEVELOPS SOME LIGHT PRECIP
MAINLY FROM THE BLUE RIDGE EAST. THE NAM RETAINS MUCH MORE LOW LEVEL
MOISTURE AND DEVELOPS CONVECTION ON THE BLUE RIDGE AND MOVES IT
EAST. THE FORECAST IS A COMPROMISE BETWEEN THE MOSGUIDE AND THE SREF
AND WILL FEATURE A LOW END CHANCE MORE IN LINE WITH THE GFS...
FIGURING THAT EITHER WAY THERE WILL BE SOME PRECIP OUT THERE. TEMPS
REBOUND ANOTHER CATEGORY WARMER...BUT COULD BE TOO WARM IF TOO MUCH
UPSLOPE CLOUDINESS DEVELOPS EARLY IN THE DAY.

THE NEXT IN A SERIES OF WEAK HIGH PRESSURE CENTERS BRIDGES THE MTNS
TUESDAY NIGHT AND CONTRIBUTES TO THE FORMATION OF ANOTHER WEDGE-LET
BY WEDNESDAY MORNING. THE EXTENT TO WHICH YOU MIGHT CALL THIS A COLD
AIR DAMMING EVENT WILL BE DEBATABLE...AS THERE SHOULD BE NO OBVIOUS
PARENT HIGH TO THE NORTH. HOWEVER...WE SHOULD HAVE A COOL
NORTHEASTERLY FLOW AT LOW LEVELS E OF THE MTNS WHICH COULD RESULT IN
SOME LIGHT PRECIP MAINLY NEAR THE BLUE RIDGE. HAVE NUDGED THE FCST
IN THE DIRECTION OF THE SREF TO DEPICT THIS SCENARIO. TEMPS WILL
ALSO DROP OFF TWO CATEGORIES OR MORE WITH THE NORTHEAST FLOW.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 215 PM SUNDAY...THIS PERIOD BEGINS WED EVENING WITH AN UPPER
TROUGH OVER THE EAST AND A RIDGE OVER THE WESTERN STATES. ANOTHER
COLD AIR DAMMING EVENT WILL BE OCCURRING AS A 1028 MB SURFACE HIGH
WILL BE OVER THE GREAT LAKES WED EVENING AND THEN BE OVER NEW
ENGLAND THURS NIGHT. THIS SYSTEM WILL BRING A COOL AND STABLE AIR
FLOW FROM CANADA AND SOME FETCH OFF THE ATLANTIC. THIS HIGH WILL
MOVE SLOWLY EAST CROSSING NOVA SCOTIA SATURDAY MORNING WHILE STILL
RIDGING DOWN INTO THE CAROLINAS WITH A COOL NE FLOW. THIS FLOW
SHOULD CERTAINLY BREAK DOWN SUNDAY AND BECOME MORE SOUTHERLY SUNDAY
NIGHT AHEAD OF THE NEXT COLD FRONT WHICH IF FORECAST TO BE CROSSING
THE OHIO VALLEY TO START THE WEEK OF SEPTEMBER 22. THE GFS SHOWS
WEAK INSTABILITY OF AROUND 500 J/KG IN THE PIEDMONT THURS AND FRI PM
BEING MOSTLY ELBERTON TO GREENWOOD FRI...SO IF THERE IS ANY RAIN AT
ALL IT WOULD BE SHOWERS OR PATCHY LIGHT RAIN UNDER THE WEDGE. TEMPS
WILL BE THE COOLEST THURS AND FRI.  TEMPS WILL BE A BIT WARMER TO
AROUND 5 DEGREES BELOW NORMAL OVER THE WEEKEND WITH THE WEDGE
BREAKING DOWN AND THE RESULTANT OF MORE SUNSHINE.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AT KCLT...THE PRIMARY CONCERN SURROUNDS JUST HOW MUCH CIGS WILL
LOWER THIS MORNING. CONDITIONS ARE SOLIDLY MVFR AS OF 0530Z...BUT NE
FLOW JUST ABOVE THE SURFACE INDICATES SOME SLIGHTLY DRIER AIR IS
FILTERING INTO THE REGION. ON THE OTHER HAND...NEAR TERM MODEL
GUIDANCE IS IN AGREEMENT THAT THE FLOW WILL TURN TOWARD THE SW
TOWARD DAYBREAK...WHICH WOULD STOP ANY DRY AIR INFILTRATION AND
POSSIBLY ALLOW CIGS TO LOWER TO IFR. IN FACT...I THINK THERE/S
ENOUGH POTENTIAL FOR THIS TO INCLUDE A TEMPO BETWEEN 10Z AND 12Z.
SOME BR IN THE 5-6SM RANGE WILL ALSO BE POSSIBLE. OTHERWISE...CIGS
SHOULD LIFT TO VFR BY EARLY AFTERNOON...AND POSSIBLY SCATTER FROM
TIME TO TIME. AN UPPER AIR DISTURBANCE WILL BRING INCREASING
CHANCES FOR CONVECTION DURING THE EVENING...MAINLY IN THE FORM OF
SHRA. A PROB30 HAS BEE INTRODUCED TO ACCOUNT FOR THIS. LGT/VRBL
WINDS SHOULD BECOME LIGHT SW BY MID-AFTERNOON.

ELSEWHERE...OUR BEST PERFORMING GUIDANCE OVER THE PAST COUPLE OF
DAYS IS INSISTENT IN DEVELOPING LIFR (AT KAVL) AND IFR (ELSEWHERE)
CIGS WITHIN THE NEXT COUPLE OF HOURS...AND HAS PLENTY OF SUPPORT
FROM OTHER RELIABLE GUIDANCE. HOWEVER...CIGS HAVE ACTUALLY BEEN
SLOWLY LIFTING OVER THE PAST COUPLE OF HOURS. THERE IS ALSO
INDICATION THAT THE FLOW WILL VEER TOWARD THE W/SW ABOVE THE SURFACE
(ALBEIT REMAINING LIGHT) TOWARD DAYBREAK...RESULTING IN AN INCREASED
DOWNSLOPE COMPONENT WHICH WOULD BE A LIMITING FACTOR FOR CIGS
LOWERING MUCH FURTHER. NEVERTHELESS...WE ARE STARTING TO SEE PATCHY
FEW/SCT IFR CLOUDS SHOWING UP ON AREA METARS...SO TEMPOS FOR IFR
HAVE BEEN ADDED FOR AT LEAST A COUPLE OF HOURS THROUGH DAYBREAK.
KHKY SEES THE SHORTEST TEMPO (2 HOURS) DUE TO STRONGER EFFECTS FROM
DOWNSLOPING. MEANWHILE...KAVL IS ALREADY LIFR AND SHOULD REMAIN SO
THE REST OF THE NIGHT...ALTHOUGH WOULD NOT BE SURPRISED TO SEE THEM
VARY QUITE A BIT...ES ONCE THE W/SW FLOW BECOMES ESTABLISHED. AN
UPPER AIR DISTURBANCE WILL BRING INCREASING CHANCES FOR
CONVECTION TO WESTERN AREAS BY LATE AFTERNOON...CONTINUING THROUGH
THE END OF THE PERIOD. A PROB30 FOR TSRA HAS BEEN INTRODUCED TO
ACCOUNT FOR THIS.

OUTLOOK...SCT SHOWERS/THUNDERSTORMS WILL CONTINUE INTO EARLY TUE...
WHILE FLT RESTRICTIONS MAY DEVELOP AGAIN TUE MORNING IN LOW CLOUDS
AND/OR FOG. A RETURN TO MAINLY VFR CONDITIONS IS EXPECTED LATER TUE
INTO MIDWEEK OUTSIDE OF RESTRICTIONS WITH DIURNAL CONVECTION.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  87%     MED   75%     HIGH  97%     HIGH 100%
KGSP       MED   69%     MED   73%     HIGH  83%     HIGH  97%
KAVL       MED   78%     MED   78%     HIGH  88%     HIGH  90%
KHKY       MED   64%     MED   71%     HIGH 100%     HIGH  94%
KGMU       MED   69%     MED   77%     HIGH  86%     HIGH  98%
KAND       HIGH  83%     HIGH  94%     HIGH  92%     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...JAT/JDL/NED
SHORT TERM...PM
LONG TERM...DEO
AVIATION...JDL






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