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Area Forecast Discussion

598
FXUS62 KGSP 230123
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
823 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 815 PM...THE RADAR MOSAIC IS BEGINNING TO FILL IN ACRS
SRN/CENTRAL GA AND SRN SC THIS EVENING...PERHAPS A HAIR AHEAD OF
SCHEDULE. ALREADY SOME PATCHY STRATUS DEVELOPING ACRS THE UPSTATE
AND CENTRAL NC MTNS THIS EVENING...INDICIATIVE OF THE INCREASING
MOISTURE AND ISENT LIFT. I TWEAKED THE POP/WX GRIDS TO MATCH UP A
LITTLE BETTER WITH THE TRENDS. TEMPS ARE RUNNING A LITTLE COLDER
ALONG AND N OF I-40...WHERE SKIES ARE CLEAR...BUT WARMER TO THE
SOUTH WITHIN THE CLOUD COVER. SO TEMPS WERE ALSO ADJUSTED. ALREADY A
FEW LWR 30 DEG READINGS IN SOME OF THE HIGH-ELEVATION VALLEYS.
HOWEVER...LOOKING AT THE 00Z FFC/GSO SOUNDINGS...AND THE INCREASING
TEMP AND DWPTS IN THE HIGHEST ELEVATIONS...I STILL THINK GOING WITH
ALL-LIQUID PRECIP IS GOOD...AS WAA SHUD QUICKLY BRING TEMPS ABOVE
FREEZING ACRS ALL SITES OVERNIGHT.

AS OF 645 PM...NO SIGNIFICANT CHANGES WITH THIS UPDATE. I UPDATED
THE WINDS WITH THE LATEST NAM FOR THE 00Z TAFS. ALSO...BLENDED IN
THE OBS FOR THE TEMP AND DWPT TRENDS. I WILL REVISIT THE TIMING OF
POP FROM SW TO NE TNGT FOR THE NEXT UPDATE. ALSO...SOME CONCERN THAT
TEMPS WILL BE ABLE TO DROP BELOW FREEZING IN PORTIONS OF THE NRN NC
MTNS AND FOOTHILLS...ONCE IN SITU COLD AIR DAMMING STARTS LATE TNGT.
THAT MAY INTRODUCE A SMALL CHANGE OF SOME FREEZING RAIN.
HOWEVER...LATEST GUIDANCE...ESP THE HI-RES SIMULATED
REFLECTIVITY...SEEM TO BE A BIT SLOW ON PRECIP ONSET.

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 SATURDAY/...
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 /02Z SUNDAY THROUGH THURSDAY/...
AT KCLT...CONDITIONS WILL START OUT VFR THIS EVENING...BUT THEN
GRADUALLY DETERIORATE SUNDAY MORNING...AS COPIOUS AMOUNTS OF
MOISTURE MOVES IN FROM THE SOUTH AHEAD OF AN APPROACHING LOW PRES
SYSTEM. MID CLOUD CIGS SHUD DEVELOP OVERNIGHT...THEN MVFR TO IFR
CIGS WITH ONSET OF RAIN BY AROUND DAYBREAK. RAIN SHOULD BE FAIRLY
STEADY FOR MOST OF THE DAY ON SUNDAY. WINDS WILL START OUT SE...BUT
TURN BACK TO NE...AS AN IN SITU COLD AIR DAMMING WEDGE DEVELOPS WITH
ONSET OF PRECIP. WINDS WILL BE CLOSE TO DUE EAST...BUT EXPECTED TO
FAVOR AN ENE DIRECTION.

ELSEWHERE...SIMILAR TO KCLT PARAGRAPH ABOVE...EXCEPT SLGT TIMING
DIFFERENCES WITH ONSET OF MVFR TO IFR CIGS AND PRECIP ONSET. PRECIP
AND LOW CIGS SHUD DEVELOP FROM SW TO NE LATE TNGT THRU SUNDAY
MORNING ACRS THE REGION. INCREASING SELY LLVL FLOW MAY BE ENUF FOR
LLWS AT KAVL DURING THE MID-TO-LATE MORNING HOURS. COLD AIR DAMMING
SHUD KEEP WINDS NE ACRS THE PIEDMONT...AND SE AT KAVL. A FEW LOW-END
GUSTS POSSIBLE ACRS THE UPSTATE...ESP AT KAND LATE MORNING TO MIDDAY.

OUTLOOK...RESTRICTIVE CIGS AND PRECIPITATION WILL CONTINUE TO BE
WIDESPREAD SUNDAY NIGHT 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...

            01-07Z        07-13Z        13-19Z        19-00Z
KCLT       HIGH 100%     HIGH  93%     HIGH  86%     MED   76%
KGSP       HIGH 100%     HIGH  90%     MED   76%     HIGH  84%
KAVL       HIGH 100%     HIGH  95%     HIGH  84%     HIGH  96%
KHKY       HIGH 100%     HIGH  91%     HIGH  88%     HIGH  86%
KGMU       HIGH 100%     HIGH  88%     MED   78%     HIGH  84%
KAND       HIGH 100%     HIGH  93%     HIGH  96%     HIGH  84%

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



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