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Area Forecast Discussion

068
FXUS62 KGSP 261157
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
657 AM EST WED NOV 26 2014

.SYNOPSIS...
LOW PRESSURE WILL INTENSIFY ALONG A STALLED COLD FRONT OFF THE
ATLANTIC SEABOARD AND MOVE UP THE COAST TODAY. AN UPPER LEVEL SYSTEM
WILL CROSS WESTERN NORTH CAROLINA EARLY THURSDAY. DRY HIGH PRESSURE
WILL RETURN FRIDAY AND LINGER INTO THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AS OF 650 AM...REPORTS FROM THE HIGH ELEVATIONS INDICATE PRECIP IS
FINALLY TRANSITIONING TO SNOW ALONG THE BACK EDGE OF THE PRECIP
SHIELD ACROSS THE HIGH ELEVATIONS OF THE SRN/CTRL NC MTNS. PRETTY
DECENT SNOWFALL RATES HAVE BEEN REPORTED...SO SOME AREAS COULD PICK
UP A QUICK COUPLE OF INCHES BEFORE ENDING. CONSIDERING CONDITIONS
ARE IN A BIT OF A STATE OF FLUX RIGHT NOW...WILL NOT ALTER THE WSW
PRODUCTS ATTM...BUT THESE WILL PROBABLY BE CANNED BY MID-MORNING. IT
STILL APPEARS THAT MINIMAL SNOWFALL (OR EVEN OCCURRENCE OF SNOW)
WILL BE SEEN BELOW ABOUT 3000 FEET.

OTHERWISE...THE BACK EDGE OF THE PRECIP SHIELD WILL CONTINUE TO WORK
ITS WAY STEADILY ACROSS THE FORECAST AREA THIS MORNING...AND WILL
LIKELY EXIT THE FORECAST AREA BY NOON OR SO.

PREVIOUS DISCUSSION...

PRECIP EVENT IS UNFOLDING MORE OR LESS AS PLANNED...WITH ONE
CAVEAT...THERE/S NO COLD AIR BELOW ABOUT 4000 FEET AT THIS TIME...
AND IT/S BECOMING INCREASINGLY DIFFICULT TO FIGURE OUT WHERE IT/S
GOING TO COME FROM. TEMPS ARE IN THE 40S ACROSS MUCH OF THE MTN
VALLEYS...AND EVEN IN AVERY COUNTY THERE IS NOTHING BUT LIQUID
FALLING BENEATH THE ELEVATION OF BEECH MOUNTAIN. LATEST 88D
INDICATES HEAVIER PRECIP RATES SETTING UP ACROSS THE FOOTHILLS ATTM
(WHICH LOOKS SCARIER THAN IT ACTUALLY IS ON RADAR DUE TO BRIGHT
BANDING)...SO I SUPPOSE ITS NOT OUT OF THE QUESTION THAT ADDITIONAL
COOLING BROUGHT ABOUT BY THESE HEAVIER RATES COULD RESULT IN A
TRANSITION TO SNOW ALONG THE ESCARPMENT...BUT EVEN THIS ISN/T
APPEARING TOO LIKELY ATTM. THE LATEST NAM GUIDANCE CONTINUES TO
POUND THE TABLE RE: A FAIRLY WIDESPREAD SNOW EVENT THIS MORNING
ACROSS THE MTNS...BUT IT HAS THUS FAR VERIFIED MUCH TOO COLD...AND
AGAIN...BASED ON UPSTREAM OBSERVATIONS...I JUST DON/T SEE WHERE ALL
THIS COLD AIR IS GOING TO COME FROM. IT HAS ALSO GOTTEN TO THE POINT
WHERE THE NAM APPEARS TO BE A LONE VOICE IN THE WILDERNESS...AS THE
LATEST RAP/GFS GUIDANCE ARE VERY WARM THIS MORNING...AND EVEN THE
00Z ECMWF HAS CONTINUED ITS WARMING TREND.

HAVING SAID ALL THAT...IN COLLABORATION WITH MRX/RNK...WE/VE DECIDED
TO TAKE A WAIT AND SEE APPROACH BEFORE MAKING RADICAL CHANGES TO THE
WSW SUITE. ONE ACTION WE WILL TAKE IS TO CHANGE THE ADVISORY FOR
MADISON/BUNCOMBE COUNTIES BACK TO A HIGH-ELEVATION PRODUCT.

OTHERWISE...PRECIP WILL BEGIN TO END RATHER QUICKLY AFTER 12Z THIS
MORNING...AS UPPER LEVEL VORT MAX COMES SLAMMING THROUGH THE
AREA...AND PUSHES DEVELOPING SURFACE CYCLONE UP TOWARD THE MID-
ATLANTIC COAST. WESTERN AREAS WILL LIKELY SEE SOME SUN BY
AFTERNOON... ALLOWING TEMPS TO WARM TO THE LOWER/MID 50S ACROSS THE
UPPER SAVANNAH RIVER VALLEY...WITH MID/UPPER 40S EXPECTED IN THE MTN
VALLEYS AND ACROSS THE NC PIEDMONT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
AS OF 300 AM WED...JUST AS QUICKLY AS THE COASTAL LOW PULLS AWAY FROM
THE PIEDMONT THIS AFTN...THE NEXT SYSTEM ENTERS FROM THE WEST IN THE
FORM OF A CLIPPER SHORTWAVE ROLLING THRU THE REGION TONIGHT. MODELS
CONTINUE TO SHOW A BRIEF BUT POTENT SHOT OF Q-VECTOR CONVERGENCE AND
OMEGA WITH THIS WAVE ALONG WITH FAIRLY DEEP MOISTURE. PROFILES WILL
BE COLD ENOUGH FOR ALL SNOW IN HIGHER ELEVATIONS AT THE ONSET OF THE
FORCING AND POPS. MOST OF THE AREA HOWEVER WILL STILL BE TOO WARM FOR
SNOW AND REMAIN SO THRU THE EVENT.

TRENDS IN THE LOW LEVEL FLOW ARE A LITTLE COMPLEX WITH A VERY SHORT
RIDGE AND WEAK WAA COMING BETWEEN THE TWO TROUGHS. THERE WAS SOME
INDICATION FROM PREVIOUS MODEL RUNS THAT THIS WAA MIGHT CAUSE A SMALL
WARM NOSE TO DEVELOP AND ALLOW FOR SLEET/FZRA IN SOME OF THE
FOOTHILLS. LATEST RUNS INDICATE THIS WAA IS TOO WEAK TO HAVE SUCH AN
EFFECT AND WE WILL ADVERTISE AN ALL RAIN/SNOW EVENT. SNOW LEVELS ARE
EXPECTED TO DROP SOMEWHAT STEADILY OVERNIGHT WITH WET BULB EFFECTS
PROVIDING ONLY MARGINAL ENHANCEMENT. WITH OR JUST AFTER THE CLIPPER
AXIS PASSES EARLY THANKSGIVING MRNG...WINDS VEER TO NW AND REMAIN
BRISK THROUGH THE LOWEST FEW THSD FT WHICH SHOULD PROVIDE A JUMP IN
PRECIP RATES. THE NW WINDS CONTINUE TO BE STRONG THRU THURSDAY ALBEIT
WITH MOISTURE SLOWLY BECOMING MORE SHALLOW.

DESPITE THE STRONG FORCING MODEL QPF IS NOT THAT STRONG BUT I DID
FAVOR THE HIGHER AND MORE TERRAIN-ORIENTED NAM QPF AS PART OF A BLEND
OF RAW MODEL AND WPC QPF. TOTAL ACCUMS OF 1 TO 2 INCHES ARE EXPECTED
IN THE SMOKIES AND BALSAMS...AND 2 TO LOCALLY 3 INCHES IN THE MTNS
NORTH OF THE FRENCH BROAD. HALF OF THAT WILL PROBABLY FALL IN A SHORT
PERIOD WHEN THE TWO FORCING MECHANISMS OVERLAP. GIVEN THE HOLIDAY AND
POTENTIAL TRAVEL IMPACTS A WINTER WX ADVISORY WILL BE HOISTED FOR OUR
TENN BORDER ZONES IN ADDITION TO NRN JACKSON COUNTY MIDNIGHT TO NOON
THANKSGIVING DAY. ENOUGH WARMING SHOULD OCCUR DURING THE DAY THAT
MOST VALLEYS WILL SEE RAIN MIX IN OR A COMPLETE TRANSITION. LIGHT
SHSN COULD CONTINUE THRU FRI MRNG THOUGH MOISTURE IS INSUFFICIENT TO
EXPECT MUCH ADDITIONAL ACCUM.

DRY HIGH PRESSURE WILL FILTER IN THU NIGHT INTO FRI. MIN TEMPS FRI
MRNG WILL BE IN THE L20S MTNS AND U20S TO AROUND 30 IN THE PIEDMONT.
SKIES WILL BE MOSTLY CLEAR BY THIS TIME...BUT CONTINUED NLY WINDS
WILL KEEP TEMPS FROM RISING OUT OF THE 40S OVER MOST OF THE AREA FRI
AFTN. SLIGHT RETURN FLOW SETS UP FRI NIGHT WHICH WILL KEEP TEMPS FROM
PLUNGING AS MUCH...ALSO INTRODUCING A LITTLE CLOUD COVER INTO THE
AREA.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 220 AM WEDNESDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z ON
SATURDAY WITH A RELATIVELY ZONAL UPPER PATTERN OVER MOST OF THE
CONUS. AS WE MOVE INTO SUN...ANOTHER BROAD H5 TROF DIGS DOWN OVER
THE FAR NORTHERN STATES AND THEN OVER THE GREAT LAKES. AT THE SAME
TIME...FLAT UPPER RIDGING WILL PERSIST SPREAD OVER THE GULF OF MEX
AND PERSIST OVER THE REGION THRU MOST OF THE PERIOD. THE LONG RANGE
GUIDANCE ACTUALLY HAS THE RIDGE AMPLIFYING TOWARDS THE VERY END OF
THE MEDIUM RANGE.

AT THE SFC...HIGH PRESSURE WILL BE CENTERED OVER THE FCST AREA AT
THE START OF THE PERIOD WITH WARMER SLY FLOW INCREASING THICKNESSES
AND TEMPS OVER THE WEEKEND. THE NEXT FRONTAL SYSTEM WILL APPROACH
THE AREA BY EARLY MON AND LAY DOWN ACROSS OUR NORTHERN FRINGE.
STRONG HIGH PRESSURE BEHIND THE FRONT WILL SLIDE EASTWARD AND
APPEARS TO SET UP A POTENTIALLY STRONG CAD PATTERN TO OUR NE BY DAY
7. THE ECMWF AND CANADIAN OPERATIONAL MODELS REMAIN MORE MOIST WITH
THIS FRONT AND SUBSEQUENT WEDGE PATTERN...YET AS WE HAVE SEEN MANY
TIMES BEFORE...MODELS TEND TO OVERESTIMATE THE EXTENT OF THE DEEPER
LYR MOISTURE IN THESE SCENARIOS. WITH THAT SAID...THE ONLY POPS I
HAVE ARE SLIGHT TO LOW END SOLID CHANCE FROM LATE SUN ONWARD. THE
BEST CHANCES ARE STILL OVER THE HIGHER TERRAIN AND ALONG THE NC/TENN
BORDER REGION. TEMPS WILL WARM THRU MON WITH VALUES EXCEEDING
CLIMATOLOGY. VALUES SHOULD COOL AGAIN AS WE GO INTO MID WEEK AND THE
FLOW BECOMES MORE NELY.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...IFR/LIFR CIGS FINALLY DEVELOPED WITHIN THE PAST HOUR...AND
ARE EXPECTED TO COME IN AND OUT OVER THE FIRST FEW HOURS OF THE
PERIOD...WARRANTING A TEMPO THROUGH 15Z. OTHERWISE...OCCL MVFR VISBY
RESTRICTIONS IN -RA WILL CONTINUE AS WELL...WITH RAIN EXPECTED TO
TAPER OFF BY NOON. MVFR CIGS SHOULD THEN LIFT TO VFR NO LATER THAN
MID-AFTERNOON. VFR CLOUDS SHOULD THEN LINGER INTO THE OVERNIGHT...AS
MOISTURE PERSISTS IN ADVANCE OF A SECONDARY UPPER AIR DISTURBANCE.
THIS MAY BRING A STRAY RAIN SHOWER NEAR THE TERMINAL TONIGHT...BUT
PROBABILITY APPEARS TO REMOTE TO INCLUDE IN THE TAF ATTM. WINDS WILL
REMAIN NORTHERLY...THIS MORNING...INCREASING TO AROUND 10 KTS...THEN
TURNING GRADUALLY TOWARD THE NW AS SURFACE LOW PRESSURE MOVES UP THE
MID-ATLANTIC COAST.

ELSEWHERE...SPORADIC IFR/LIFR CIGS HAVE DEVELOPED ACROSS THE AREA
THIS MORNING...AND OCCL CIGS WILL PERSIST AT THIS LEVEL THROUGH 14
OR 15Z...WARRANTING A TEMPO THROUGH THAT TIME. OTHERWISE...OCCL MVFR
VISBY RESTRICTIONS IN -RA WILL CONTINUE AS WELL...WITH RAIN EXPECTED
TO TAPER OFF BY 15Z OR SO AT MOST TERMINALS. SNOW IS NO LONGER
EXPECTED TO MIX WITH THE RAIN AT KAVL. MVFR CIGS SHOULD THEN LIFT TO
VFR BY NOON-ISH. VFR CLOUDS SHOULD THEN LINGER INTO THE
OVERNIGHT...AS MOISTURE PERSISTS IN ADVANCE OF A SECONDARY UPPER AIR
DISTURBANCE. THIS MAY BRING A STRAY RAIN SHOWER NEAR THE TERMINALS
(SNOW SHOWERS POSSIBLE AT KAVL) TONIGHT...BUT PROBABILITY APPEARS TO
REMOTE TO INCLUDE IN THE TAF ATTM.

OUTLOOK...A DRY AIR MASS WILL THEN RETURN TO THE AREA BY LATE
THURSDAY AND CONTINUE THROUGH THE WEEKEND.

CONFIDENCE TABLE...

            12-18Z        18-24Z        00-06Z        06-12Z
KCLT       HIGH  83%     HIGH  95%     HIGH 100%     HIGH 100%
KGSP       HIGH  82%     HIGH  94%     HIGH 100%     HIGH 100%
KAVL       HIGH  82%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH  83%     HIGH  94%     HIGH 100%     HIGH 100%
KGMU       HIGH  83%     HIGH  98%     HIGH 100%     HIGH 100%
KAND       HIGH  88%     HIGH  98%     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...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ048-
     051>053-059-063-064-501-503-505.
     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
     THURSDAY FOR NCZ033-048>052-058-059.
     WINTER STORM WARNING UNTIL NOON EST TODAY FOR NCZ033-049-050.
SC...NONE.

&&

$$
SYNOPSIS...JDL
NEAR TERM...JDL
SHORT TERM...WIMBERLEY
LONG TERM...JPT
AVIATION...JDL



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