Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 130858
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
458 AM EDT SAT SEP 13 2014

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

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 430 AM EDT...CLUSTER OF SHOWERS WITH A COUPLE EMBEDDED TSTMS
REMAINS OVER THE I-77 CORRIDOR AND AREAS JUST WEST. ISENTROPIC LIFT
ATOP WEAK WEDGE OF HIGH PRESSURE DOES APPEAR TO BE WANING AS THE 00Z
MODELS SUGGESTED IT WOULD AROUND THIS TIME...ALLOWING THE STRATIFORM
PRECIP TO DIMINISH. THE CONVECTIVE ACTIVITY LOOKS LIKE IT MAY BE
FORCED BY A WEAK WAVE OF LOW PRESSURE INVOF WITH THE COLD FRONT
EXTENDING DOWN FROM THE MIDWEST SYSTEM DESCRIBED BELOW. AT ANY RATE
IT APPEARS PRECIP CHANCES WEST OF THAT LINE ARE LOW ENOUGH NOT TO
MENTION IN THE VERY NEAR TERM. HOWEVER INCREASING ACTIVITY JUST W OF
THE MTNS SUGGESTS POPS WILL RAMP UP QUICKLY THIS AM IN THE TENN
BORDER ZONES. ON ANOTHER NOTE...THOUGH SFC OBS DO NOT INDICATE DENSE
FOG...THE RAPID AND LARGE CHANGES IN VSBY SEEN HERE AT GSP AND AT
SURROUNDING SITES SUGGESTS THERE MAY BE SOME LOCALLY DENSE FOG OUT
THERE. UNLESS SFC OBS BEGIN TO SHOW A CONTIGUOUS AREA OF 1/4SM
VSBY...NO ADVY WILL BE NEEDED. HOWEVER CAUTION IS ADVISABLE ON RURAL
ROADS AND IN VALLEYS.

AFTER SUNRISE...LOW PRESSURE WILL DEEPEN OVER THE UPPER OH VLY IN
RESPONSE TO THE SHARP SHORTWAVE OVER THE GREAT LAKES REGION. A COLD
FRONT EXTENDS SWD FROM THAT LOW AND WILL CROSS THE MTNS AROUND
MIDDAY. IT WILL THEN PROGRESS ACRS THE CWFA THIS AFTN/EVENING ACTING
TO FOCUS CONVECTION. THE FRONT IS THEN EXPECTED TO STALL OUT ACROSS
SC BY SUNDAY MRNG ALLOWING ANOTHER WEDGE TO FORM AS HIGH PRESSURE
MOVES FROM THE MISSISSIPPI VALLEY TO THE EAST COAST.

POPS TODAY WILL PEAK EARLIER THAN CLIMO IN THE MTNS BEFORE COLD
ADVECTION INHIBITS CONVECTION...BUT ABUNDANT MOISTURE AND UPSLOPING
WARRANT KEEPING A MENTIONABLE POP THRU THE NEAR TERM. OVER THE
FOOTHILLS/PIEDMONT MODELS PRODUCE MODEST CAPES OF 1000-1500 J/KG
STILL WITH WEAK SHEAR...AS ANY SIGNIFICANT UPPER FEATURES REMAIN WELL
TO OUR NORTH DURING THE PERIOD. THERE IS HOWEVER ENOUGH FLOW ALOFT TO
KEEP CELLS MOVING TO SOME DEGREE. PWAT VALUES WILL BE ELEVATED...ESP
IN THE LOWER PIEDMONT WHERE THEY WILL REMAIN NEAR 2 INCHES.  THEY
WON/T BE QUITE AS HIGH AS THOSE FRIDAY AND THE FLOW WILL BE AT A
LARGER ANGLE TO THE FRONT. ALTOGETHER THE FLOOD RISK IS NOT THAT
GREAT...THOUGH LOCALIZED FLOODING IS STILL A POSSIBILITY ESPECIALLY
IN URBAN ENVIRONMENTS. THE BRIEF BREAK IN THE WEDGE SHOULD ALLOW
CLOUDS TO LIFT BUT NOT BREAK UP...AND TEMPS WILL BE NEAR TO SLIGHTLY
ABOVE NORMAL.

TONIGHT...WITH A WEDGE AGAIN SETTING UP...WEAK UPGLIDE RETURNS AS THE
LOW LIFTS AWAY AND THE BERMUDA HIGH REGAINS INFLUENCE ACRS THE
SOUTHEAST. THUS HAVE ALLOWED CHANCE POPS TO PERSIST OVER MUCH OF THE
PIEDMONT OVERNIGHT. EASTERLY FLOW WILL PROVIDE SOME ENHANCEMENT INTO
THE BLUE RIDGE AS WELL. LAPSE RATES ARE RATHER POOR ABOVE THE WEDGE
INVERSION SO IT APPEARS THUNDER WILL BE OF LITTLE CONCERN ONCE IT
DEVELOPS. ONLY LIGHT QPF WILL BE ADVERTISED. THOUGH THEY WILL BE
COOLER THAN THOSE SATURDAY MRNG WITHIN THE POSTFRONTAL AIRMASS...MIN
TEMPS STILL WILL BE A CATEGORY OR SO ABOVE NORMAL UNDER CLOUDY SKIES.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 310 AM SATURDAY...A BRIEF BUT SIGNIFICANT COLD AIR DAMMING
EVENT IS ANTICIPATED FOR SUNDAY...AS WEAKENING/MIGRATORY HIGH
PRESSURE OOZES ACROSS THE NORTHEAST CONUS. WHILE CONFIDENCE IS
REASONABLY HIGH THAT MAXES SUNDAY WILL BE 10-15 DEGREES BELOW
CLIMO...THERE IS UNCERTAINTY REGARDING HOW MUCH PRECIP WILL AFFECT
THE CWA SUNDAY. THE AIR MASS IS EXPECTED TO BE VERY STABLE...WITH
THE EXCEPTION OF THE WESTERN MNTNS...AND PERHAPS THE SOUTHERN TIER
OF THE FORECAST AREA. ALTHOUGH MOISTURE WITHIN THE WEDGE AIR MASS
WILL BE ABUNDANT...UPGLIDE OVER THE COOL DOME WILL NOT BE ESPECIALLY
SIGNIFICANT. WHILE SCT CONVECTION WILL BE POSSIBLE AROUND THE
PERIPHERY OF THE CAD AIR MASS...THERE MAY BE MORE OF A PATCHY
DRIZZLE/SPOTTY -RA SCENARIO OVER THE VAST MAJORITY OF THE FORECAST
AREA. WE DIDN/T DEVIATE TOO MUCH FROM THE INHERITED 30-40 POPS...BUT
ANY PRECIP AMOUNTS SHOULD BE VERY LIGHT ACROSS THE VAST MAJORITY OF
THE FORECAST AREA.

OTHERWISE...WEDGE EROSION SHOULD BE IN FULL EFFECT BY MONDAY...AS
THE WEAKENING PARENT HIGH SLIDES OFF THE NEW ENGLAND COAST. WITH
MOISTURE LINGERING...ADDITIONAL HEATING TUE AFTERNOON SHOULD PROVIDE
THE NECESSARY INGREDIENTS FOR SCATTERED CONVECTION...AND 30-50 POPS
WILL BE MAINTAINED ACROSS MUCH OF THE AREA MON AFTERNOON INTO THE
EVENING HOURS.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 2 PM FRIDAY...THE MEDIUM RANGE FCST PICK UP AT 00Z ON TUESDAY
WITH A BROAD...LONGWAVE UPPER TROF OVER THE EASTERN HALF OF THE
CONUS AND UPPER RIDGING OVER THE WEST. THE OVERALL PATTERN IS NOT
EXPECTED TO CHANGE SIGNIFICANTLY THRU THE PERIOD WITH SOME
DEAMPLIFICATION LIKELY BY DAYS 6 AND 7 AS THE RIDGE AXIS DRIFTS
FARTHER EASTWARD.

AT THE SFC...THE REGION IS EXPECTED TO BE UNDER A BROAD AREA OF WEAK
LOW LVL CONVERGENCE WITH MOIST PROFILES PERSISTING FROM THE PREVIOUS
FEW DAYS. AS ONE HIGH MOVES OFF THE NEW ENGLAND COAST...ANOTHER WILL
MOVE EASTWARD FROM THE NORTHERN PLAINS ON TUES AND THEN NORTH OF OUR
REGION BY LATE WED OR THURS. BY THE END OF THE MEDIUM RANGE...THE
HIGH WILL LIKELY HAVE MOVED OVER NEW ENGLAND AND SET UP ANOTHER COOL
AIR WEDGE OVER THE CAROLINAS. AS FOR THE SENSIBLE FCST...THE LATEST
MODEL RUNS HAVE BEEN TRENDING DRIER AND COOLER...ESPECIALLY TOWARDS
THE END OF THE PERIOD. THE GFS IS NOW MORE IN LINE WITH THE ECMWF
YET IT STILL DOES NOT DRY THE FCST AREA OUT ON WED...BUT BY THURS IT
BEGINS TO SET UP THE WEDGE PATTERN. AS FOR POPS...THE BEST CHANCES
FOR WIDESPREAD DIURNAL CONVECTION WILL BE TUES AND WED. FOR THURS
AND FRI...I ONLY CARRY A SLIGHT CHANCE POP. TEMPS WERE LOWERED EACH
DAY BY A FEW DEGREES WITH VALUES DROPPING THRU THE PERIOD. BY NEXT
FRI...HIGHS ARE NEARLY 2 CATEGORIES BELOW CLIMATOLOGY.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...SCT-NUMEROUS HEAVY SHRA WILL CONTINUE NEARBY EARLY THIS
AM. CIG SHOULD BE LOCKED IN AT LEAST IFR UNTIL MID MRNG. WINDS ALOFT
VEER AT MIDDAY AHEAD OF ANOTHER COLD FROPA EXPECTED EARLY THIS
EVENING. THIS WILL ALLOW CIGS TO LIFT...BUT DIURNAL INSTABILITY WILL
BE ABLE TO GROW WITH THAT FRONT COMING IN NEAR PEAK HEATING.
SHRA/TSRA WILL CONTINUE TO BE CAPABLE OF PROLIFIC RAINFALL AND
PERIODIC MVFR CIGS/VSBY. CAN/T RULE OUT THE RETURN OF RESTRICTIONS
TONIGHT BUT THAT IS MOST LIKELY AFTER 06Z. WINDS WILL GENERALLY BE
SOUTHERLY DURING THE DAY TODAY BUT WILL PREVAIL NE AFTER THE COLD
FRONT BRINGS IN ANOTHER WEDGE.

ELSEWHERE...MRNG PRECIP CHANCES ARE LOW ENOUGH ONLY TO MENTION IN
VCNTY. UNDER WEDGE OF COOL AIR...KHKY WILL SEE IFR CIGS/FOG CONTINUE
THRU THE MRNG WHILE OTHER SITES ARE MAINLY AT RISK NEAR DAYBREAK.
WEDGE WILL WEAKEN AND CIGS SHOULD LIFT GRADUALLY IN THE LATE MRNG.
COLD FRONT WILL MOVE THRU THE REGION ACTING TO FOCUS DIURNAL
INSTABILITY AND CONVECTIVE DEVELOPMENT. HAVE PREVAILED SHRA/TSRA
NEAR TIME OF FROPA. THE FRONT WILL THEN STALL ACRS GA/SC BASICALLY
REINFORCING THE ONE WHICH IS CURRENTLY STATIONARY THERE...AND A
WEDGE REDEVELOPS OVERNIGHT TONIGHT. RESTRICTIONS LIKELY TO DEVELOP
AT SOME POINT TONIGHT BUT THIS IS MOST LIKELY VERY NEAR IF NOT AFTER
06Z SO NO MENTION MADE AT THIS ISSUANCE.

OUTLOOK...A FRONTAL BOUNDARY WILL REMAIN STALLED ACROSS THE
SOUTHEAST THRU THE WEEKEND WHILE A WEAK WEDGE OF HIGH PRESSURE
SLIDES DOWN THE EAST SIDE OF THE MOUNTAINS. MORNING VSBY/CIG
RESTRICTIONS POSSIBLE AT ALL SITES EACH MORNING WITH THE HIGHEST
PROBABILITIES RESIDING ACROSS THE HIGH TERRAIN AND IN THE MOUNTAIN
VALLEYS.

CONFIDENCE TABLE...

            09-15Z        15-21Z        21-03Z        03-09Z
KCLT       MED   75%     HIGH  92%     HIGH 100%     HIGH 100%
KGSP       HIGH  85%     HIGH  93%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH  92%     HIGH 100%     HIGH  94%
KHKY       HIGH  86%     HIGH  82%     HIGH 100%     HIGH  94%
KGMU       HIGH  84%     HIGH  97%     HIGH 100%     HIGH 100%
KAND       MED   73%     HIGH  93%     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...WIMBERLEY
NEAR TERM...WIMBERLEY
SHORT TERM...JDL
LONG TERM...JPT
AVIATION...WIMBERLEY





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