Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 221946
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
246 PM EST SAT NOV 22 2014

.SYNOPSIS...
DRY HIGH PRESSURE WILL GIVE WAY TO A VERY MOIST SOUTHERLY FLOW ON
SUNDAY. A COLD FRONT WILL MOVE OVER THE REGION ON MONDAY WITH DRIER
AND COLDER AIR BEHIND IT. A COASTAL LOW IS THEN EXPECTED TO DEVELOP
OFF THE SOUTHEAST COAST AND MOVE UP THE ATLANTIC SEABOARD ON
WEDNESDAY AND THURSDAY. HIGH PRESSURE WILL SPREAD BACK OVER THE AREA
IN THE LOWS WAKE.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 200 PM EST SATURDAY...1033 MB HIGH PRESSURE CURRENTLY CENTERED
OVER THE EASTERN CAROLINAS WILL CONTINUE TO SLIDE OFFSHORE THROUGH
TONIGHT AS A DEVELOPING SURFACE LOW OVER THE WESTERN GULF TRACKS
NORTHEASTWARD. AS A SOUTHERN STREAM UPPER SHORTWAVE TROUGH
APPROACHES FROM THE SOUTHWEST...UPPER PATTERN BECOMES SOUTHWESTERLY
OVER THE REGION WITH MID-HIGH LVL CLOUDINESS OVERSPREADING THE
REGION IN ITS WAKE. LATEST SHORT RANGE MODELS CONTINUE TO AGREE THAT
THE LOW WILL TRACK NNE ACROSS THE MID MISSISSIPPI VALLEY AND
INTO THE GREAT LAKES REGION TONIGHT INTO SUNDAY...LIFTING AN
ASSOCIATED WARM FRONT NE ACROSS THE SOUTHERN PLAINS TONIGHT AND INTO
SOUTHERN GA/SC BY SUNDAY. ISENTROPIC UPGLIDE WILL STRENGTHEN OVER
THE REGION AHEAD OF THIS FEATURE TONIGHT AS S/SSELY LLVL JET
INCREASES ATOP THE IN-SITU CAD. AS A RESULT...PRECIP SHOULD
OVERSPREAD THE AREA FROM THE SOUTHWEST BY SUN MORNING. HEAVIER
PRECIP SHOULD OCCUR DURING THE DAY ON SUNDAY AS THE COMBINATION OF
DIFFLUENT UPPER FLOW AND IMPRESSIVE ISENTROPIC UPGLIDE PROMOTE
STRONGER LIFT AS WELL AS MAXIMIZING DEEP ATLANTIC MOISTURE FLUX OVER
THE REGION. HENCE...POPS RAMP UP FROM SW TO NE SUN MORNING AND
PEAKING CATEGORICAL RANGE THROUGH SUN AFTERNOON.

HYDRO...TOTAL RAINFALL SHOULD RANGE FROM 1.5-2 INCHES OVER THE
BLUE RIDGE ESCARPMENT TO 1 TO 1.5" ELSEWHERE. GIVEN PROLONGED DRY
CONDITIONS AND +3.5" OF 6HR FLASH FLOOD GUIDANCE OVER MUCH OF THE
AREA...THE THREAT FOR FLASH FLOODING APPEARS MINIMAL...THOUGH
ISOLATED FLOODING CAN NOT BE RULED OUT IN LOW LYING/POOR DRAINAGE
URBAN AREAS.

SEVERE WEATHER POTENTIAL...ALTHOUGH WILL BE VERY STRONG WIND SHEAR
ALOFT AND LONG CURVY HODOGRAPH...THE THREAT FOR SEVERE WEATHER
APPEARS UNLIKELY THANKS TO PERSISTENT IN-SITU CAD AND THE LACK OF
DEEP UPPER FORCING. HOWER...HAVE CARRIED THUNDER MAINLY EAST OF THE
MTNS ZONES AS MODELS DEPICT WEAK ELEVATED BUOYANCY REGIME EXTENDS
NORTHWARD TOWARD LATE SUN AFTERNOON.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 230 PM SATURDAY...THE TIMING OF THE PASSAGE OF A STRONG SHORT
WAVE HAS SLIPPED JUST A BIT INTO SUNDAY EVENING...WHICH DELAYS THE
DEPARTURE OF THE MAIN PRECIP AREA...SO A CATEGORICAL POP WAS KEPT
INTO THE EVENING HOURS OVER THE ERN HALF OF THE FCST AREA...WITH
LIKELY W OF THERE. OUR MAIN CONCERN CONTINUES TO BE THE THREAT FOR
SEVERE STORMS...PRIMARILY OVER THE AREA S/E OF I-85. THE OPERATIONAL
MODELS SUGGEST THAT OUR IN-SITU WEDGE WILL BREAK DOWN/ERODE FROM THE
SE LATE IN THE DAY ALLOWING FOR SOME WEAK BOUYANCY TO CREEP INTO THE
SE FRINGE OF THE FCST AREA. THUS...THE MODEL TREND LOOKS TO BE
POINTED TOWARD A BIT MORE INSTABILITY...TO GO ALONG WITH THE VERY
STRONG SHEAR. HOWEVER...THE EXPECTED DEGREE OF ORGANIZATION STILL
APPEARS TO BE LACKING. IN TYPICAL EVENTS WHERE WE SEE SEVERE WEATHER
FROM LINEAR CONVECTION IN HIGH SHEAR LOW CAPE ENVIRONMENTS...WE TEND
TO HAVE A VERY STRONG ADVECTIVE SHORT WAVE THAT TRACKS RIGHT ACROSS
THE FCST AREA. THIS WAVE TRACKS PAST THE MTNS TO THE NW SUNDAY EVE.
FURTHERMORE...AN EXPERIMENTAL INDEX FOR HIGH SHEAR LOW CAPE SEVERE
WEATHER (CALLED THE SHERB INDEX)...HAS VALUES BELOW WHAT IS EXPECTED
FOR AN ENVIRONMENT THAT SUPPORTS SEVERE WEATHER...WHEN RUN FOR THE
OPERATIONAL NAM AND GFS. WILL INCLUDE A CHANCE FOR THUNDERSTORMS
OVER THE SE ZONES IN THE EVENING. BOTTOM LINE...WE CANNOT TOTALLY
RULE OUT SEVERE WEATHER OVER THE SE ZONES...BUT UNLESS WE SEE MORE
INSTABILITY OR A BETTER INDICATION OF STORM ORGANIZATION...WE WILL
NOT MENTION THE NON-ZERO SEVERE WEATHER CHANCES IN THE HWO. AS FOR
HEAVY RAIN...CANNOT RULE OUT SOME HEAVY RAIN NEAR THE BLUE RIDGE IN
THE EVENING AS A STRONG LOW LEVEL JET REMAINS DIRECTED AT THE
MTNS...BUT THE 850MB FLOW VEERS QUICKLY SW IN THE EVE AS THE WAVE
PASSES. ANTECEDENT CONDITIONS ARE DRY...WHICH LOWERS OUR FLOOD RISK.
TEMPS ARE INTERESTING SUNDAY EVE/NIGHT WITH THE DESTRUCTION OF THE
WEAK WEDGE AND CONTINUED WARM ADVECTION. EXPECT THAT MOST PLACES
WILL HAVE THEIR HIGH FOR SUNDAY AFTER SUNSET AS TEMPS CONTINUE TO
RISE. TEMPS SHOULD REMAIN MILD OVERNIGHT AS THE MAIN FRONT REMAINS
TO THE WEST. ON MONDAY...THERE ARE SOME MODEL DISCREPANCIES AS TO
THE AMOUNT OF SHOWER ACTIVITY...WITH THE GFS/ECMWF SHOWING LESS
PRECIP THAN THE NAM. WILL KEEP A LOW CHANCE FIRST THING AND
GRADUALLY TAPER IT DOWN FROM THERE...MAINLY BECAUSE THE FRONT SHOULD
PASS THROUGH DURING THE DAY. FEEL THE NAM IS WAY OVERDONE BECAUSE IT
KEEPS SFC DEWPOINT VALUES IN THE LOWER TO MIDDLE 60S E OF THE MTNS
WHICH RESULTS IN TOO MUCH INSTABILITY WHICH TRIGGERS THE CONVECTIVE
PRECIP SCHEME. THE GFS LOOKS MORE REASONABLE WITH MID/UPPER 50S
DEWPOINTS...SO QUITE A BIT LESS CONVECTIVE PRECIP.

THE REST OF THE SHORT RANGE IS QUIET. WE STAY IN A SW FLOW ALOFT
WITH NO MID/UPPER FORCING AND HIGH PRESSURE BUILDING IN FROM THE
WEST. SOME LINGERING LIGHT PRECIP OVER THE TN BORDER ZONES SHOULD
END MONDAY EVENING AND AFTER THAT THE FCST WAS KEPT DRY. ANY
DEVELOPMENT CLOSER TO THE OLD STALLED FRONT OFF THE E COAST SHOULD
STAY TO OUR EAST. TEMPS TUESDAY WILL BE 10-15 DEGREES COOLER THAN
MONDAY.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
AS OF 2 PM SATURDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
WEDNESDAY WITH BROAD AND DEEP UPPER TROFFING CENTERED JUST TO OUR
WEST. OVER THE NEXT 24 TO 36 HRS...THE TROF AXIS IS EXPECTED TO LIFT
NE OF THE FCST AREA WITH SOME DEGREE OF DEAMPLIFICATION IN ITS WAKE.
THE LONG RANGE MODELS DIFFER WRT EXACTLY HOW LONG THE DEEPER TROFFING
LASTS OVER THE CWFA WITH THE ECMWF MAINTAINING A CONSIDERABLY
STEEPER TROF THRU THE FIRST HALF OR SO OF FRI WHILE THE GFS AND
CANADIAN INCREASE HEIGHTS FASTER AND FLATTEN THE UPPER PATTERN
SOONER. EITHER WAY...ALL OF THE GUIDANCE SUGGESTS THAT FROM LATE FRI
ONWARD...THE REGION WILL REMAIN UNDER A RELATIVELY ZONAL PATTERN
WITH UPPER HEIGHTS RELATIVELY CONSTANT.

AT THE SFC...THE LATEST 12Z RUN OF THE GFS IS TRENDING MORE TOWARDS
AN ECMWF-LIKE SCENARIO WRT THE DEVELOPMENT OF A SOUTHERN COASTAL LOW
ON WED. BY 18Z WED...BOTH MODELS NOW HAVE A WELL DEFINED LOW CENTERED
JUST OFF THE CAROLINA COAST WITH DEEP LYR MOISTURE SPREADING OVER
THE MAJORITY OF THE CWFA. THE ECMWF STILL MAINTAINS A LARGER...DEEP
MOISTURE PLUME OVER OUR AREA COMPARED TO THE GFS...BUT NOT BY MUCH.
BOTH MODELS AGREE THAT BY EARLY THURS...THINGS SHOULD DRY OUT PRETTY
QUICKLY AS THE LOW TRACKS UP THE EAST COAST. A WEAK SECONDARY COLD
FRONT IS EXPECTED TO PASS JUST TO OUR NORTH AS THE MAIN LOW LIFTS NE
AND SOME LINGERING PRECIP IS POSSIBLE OVER THE NORTHERN AND WESTERN
ZONES...HOWEVER IT SHOULD NOT AMOUNT TO MUCH. THE REST OF THE MEDIUM
RANGE SHOULD BE DRY WITH HIGH PRESSURE REGAINING CONTROL OVER THE
REGION. AS HIGHLIGHTED IN THE PREVIOUS DISCUSSION...MINOR AMOUNTS OF
FROZEN PRECIP ARE POSSIBLE WITH THE COASTAL LOW ON WED. MODEL
SOUNDINGS STILL SUPPORT SNOW AND/OR SNOW/SLEET OVER THE HIGHER
ELEVATIONS EARLY WED...HOWEVER BEYOND THE LATE MORNING IT LOOKS LIKE
TEMPS WILL BE TOO WARM TO SUPPORT ANYTHING BUT RAIN. IN
ADDITION...AT PRESENT THE BULK OF THE QPF IS EXPECTED OVER THE
EASTERN HALF OF THE CWFA AND NOT THE HIGHER TERRAIN. YET...THE NC
MTS COULD SEE SOME ADDITIONAL LINGERING NW FLOW SNOW WED NIGHT INTO
THURS...BUT IT LIKELY WONT BE MUCH. OTHERWISE...TEMPS START OUT
BELOW CLIMO AND REMAIN THERE THRU DAY 7.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
AT KCLT...EXPECT VFR CONDITIONS TO CONTINUE AT LEAST THROUGH EARLY
SUNDAY MORNING AS CP HIGH PRESSURE CENTERED OVER THE EASTERN
CAROLINAS CONTINUES TO SHIFT EAST. AS MOIST SWLY FLOW ALOFT DEVELOPS
IN RESPONSE TO AN APPROACHING UPPER SHORTWAVE TROUGH FROM THE
SW...EXPECT INCREASING MID-HIGH LVL CLOUDINESS THIS EVENING INTO
TONIGHT. LIGHT SE WINDS THIS AFTERNOON WILL BECOME NORTHEASTERLY BY
AROUND 03Z SUN AND STAY THAT WAY THRU THE END OF THE TAF PERIOD AS
COLD AIR DAMMING SETS UP OVER THE AREA. AS A SOUTHERN STREAM UPPER
WAVE APPROACHES THE REGION TONIGHT...ISENTROPIC UPGLIDE WILL
STRENGTHEN AND CIGS WILL BE LOWERED TO MVFR LVL BY AROUND 14Z SUN
WITH PRECIP OVERSPREADING THE REGION FROM THE SW. LATEST GUIDANCE
SUGGESTS THAT IFR CIGS IN MODERATE RAIN WILL AFFECT THE TERMINAL BY
16Z SUN AS DEEP MOISTURE/BETTER UPPER FORCING MOVE THROUGH.

ELSEWHERE...EXPECT VFR CONDITIONS TO PERSIST AT LEAST THROUGH LATE
TONIGHT/EARLY SUNDAY MORNING AS CP HIGH PRESSURE CENTERED OVER THE
EASTERN CAROLINAS CONTINUES TO SLIDE EAST. AS MOIST SWLY FLOW ALOFT
DEVELOPS IN RESPONSE TO AN APPROACHING UPPER SHORTWAVE TROUGH FROM
THE SW...EXPECT INCREASING MID-HIGH LVL CLOUDINESS THROUGH TONIGHT.
LIGHT ESE/SE WINDS THIS AFTERNOON WILL BECOME NORTHEASTERLY BY THIS
EVENING AND STAY THAT WAY THRU THE END OF THE TAF PERIOD AS COLD AIR
DAMMING SETS UP OVER THE AREA. THE EXCEPTION WILL BE KAVL WHERE
SOUTHERLY WINDS WILL PERSIST THROUGH THE PERIOD. AS A SOUTHERN
STREAM UPPER WAVE ASSOCIATED WITH A WARM FRONT APPROACHES THE
REGION...ISENTROPIC UPGLIDE WILL STRENGTHEN AND MVFR CLOUDS WITH
PRECIP WILL OVERSPREAD THE REGION FROM THE SW LATE TONIGHT INTO
EARLY SUN MORNING. LATEST GUIDANCE SUGGESTS THAT IFR CIGS...MODERATE
RAIN AND MVFR VSBY WILL AFFECT MUCH OF THE REGION BY LATE SUN
MORNING AS DEEP MOISTURE/BETTER UPPER FORCING MOVE THROUGH.

OUTLOOK...RESTRICTIVE CIGS AND PRECIPITATION WILL BE WIDESPREAD
SUNDAY AS A WARM FRONT LIFTS THRU THE REGION FROM THE SOUTH. BRIEF
DRYING FOLLOWS THE FRONT MON-TUE...WITH PRECIP POSSIBLY RETURNING
WED.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  94%     MED   78%
KGSP       HIGH 100%     HIGH 100%     HIGH  88%     HIGH  94%
KAVL       HIGH 100%     HIGH 100%     HIGH  96%     HIGH  82%
KHKY       HIGH 100%     HIGH 100%     HIGH  93%     HIGH  83%
KGMU       HIGH 100%     HIGH 100%     HIGH  86%     HIGH  94%
KAND       HIGH 100%     HIGH 100%     HIGH  88%     HIGH  90%

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...JOH
SHORT TERM...PM
LONG TERM...JPT
AVIATION...JOH


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