Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 242313
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
613 PM EST WED DEC 24 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS OUR AREA THIS EVENING. HIGH PRESSURE WILL
ARRIVE ON THURSDAY AND LINGER INTO SATURDAY. A PAIR OF COLD FRONTS
WILL APPROACH THE AREA ON SUNDAY...CROSSING THE AREA MONDAY. GUSTY
WINDS WILL FOLLOW THE FRONT ON TUESDAY.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 5 PM...REGIONAL 88D LOOPS DEPICTING JUST A SMATTERING OF
VERY LIGHT RETURNS ACRS THE CWFA WITH SYNOPTIC SCALE FEATURE OF
INTEREST BEING THE WEDGE BNDRY MAKING VERY SLOW PROGRESS INTO
THE PIEDMONT...BUT STILL JUST SE OF A KGRD-KUZA LINE. AREAS OF
DENSE FOG DID INDEED DEVELOP WITHIN THE IMMEDIATE COOL SIDE OF
THE THE WEDGE BNDRY.

AS OF 230 PM...STILL A DYNAMIC SITUATION ACROSS THE WESTERN
CAROLINAS. THE WARM CONVEYOR BELT IS ALL BUT EAST OF THE FCST AREA
AS OF 19Z...WITH THE BACK EDGE OF THE STEADIER PRECIP EXPECTED TO BE
EAST OF UNION COUNTY NC BY 20Z. THAT SHOULD TAKE CARE OF ANY
LINGERING FLASH FLOOD/SEVERE WEATHER THREAT. BEHIND THE PRECIP
BAND...CONTINUED WEAK FORCING...ESPECIALLY MOIST LOW LEVEL UPGLIDE
ABOVE A DECAYING WEDGE E OF THE BLUE RIDGE...SHOULD CONTINUE TO
FORCE SCATTERED SHOWER DEVELOPMENT THROUGH THE REST OF THE AFTERNOON
E OF THE MTNS. THE LOW LEVEL UPGLIDE SHOULD SLIDE E OF THE FCST AREA
BY EARLY EVENING...CARRYING MOST OF THE PRECIP WITH IT. PRECIP
PROBABILITIES REFLECT THIS THINKING. ANOTHER PROBLEM WILL BE THE
DESTRUCTION OF THE WEDGE...WHICH APPEARS TO BE DRAINING MORE THAN
ERODING FROM THE S BECAUSE OF THE PRECIP BAND ASSOCIATED WITH THE
WARM CONVEYOR BELT. THE WEDGE BOUNDARY HAS REACHED EQY BUT MIGHT
HAVE TROUBLE MAKING IT MUCH FARTHER NW AS WE ARE GOING TO BE LOSING
DAYTIME HEATING SOON. WITH THE WEDGE DRAINAGE AND THE LOW LEVEL
UPGLIDE...CEILINGS ARE ACTUALLY DROPPING AND VISBY IS FALLING AS THE
STRATUS LAYER GETS PUSHED TO THE GROUND. THIS COULD REQUIRE A BRIEF
DENSE FOG ADVISORY IF VISBY GETS MUCH WORSE. TEMPS WILL CONTINUE TO
BE TRICKY. MANY PLACES WILL NOT REACH THE FCST HIGH BECAUSE THE
WEDGE WILL NOT BREAK IN TIME.

OVER THE NEXT 24 HOURS...THE UPPER TROF TO THE WEST WILL DEAMPLIFY
TONIGHT AS THE BULK OF THE ENERGY LIFTS PAST WELL TO OUR N...THEN IT
CROSS THE FCST AREA CHRISTMAS MORNING. THE SURFACE FRONT WILL PUSH
ACROSS THE REGION DURING THE LATE EVENING OR EARLY MORNING HOURS.
BEHIND THE FRONT...COLDER AIR WILL FILTER IN. ENUF LOW LEVEL
MOISTURE WILL REMAIN TO BE PUSHED UP THE SLOPE ON THE TN SIDE OF THE
MTNS...SO A CHANCE POP WAS KEPT THERE. PRECIP SHOULD CHANGE OVER TO
SNOW SHOWERS THROUGH DAYBREAK. AMOUNTS WILL BE LIMITED BY THE
WESTERLY FLOW AND THE GRADUAL ARRIVAL OF COLDER AIR...SO AN ADVISORY
IS NOT PLANNED. THE DURATION WILL ALSO BE LIMITED...AS THE MODELS
DEPICT THE LOW LEVEL MOISTURE PULLING OUT AND DRYING UP BY MID
MORNING AT THE LATEST. THERE SHOULD BE SOME WEAK MID/UPPER FORCING
AS THIS MOVES THROUGH ON CHRISTMAS MORNING...BUT MOISTURE WILL BE
VERY LIMITED...SO NO PRECIP IS EXPECTED. INSTEAD...THE BULK OF THE
DAY WILL BE MOSTLY SUNNY...WITH TEMPS MAYBE A CATEGORY ABOVE NORMAL.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 215 PM EST WEDNESDAY...AN UPPER RIDGE WILL AMPLIFY OVER THE SE
THU NIGHT THROUGH FRI...WITH ITS RIDGE AXIS PUSHING OFF THE EAST
COAST BY FRI NIGHT. THE UPPER PATTERN BECOMES SWLY BY EARLY SAT AS
AN UPPER TROUGH DIGS INTO THE WESTERN CONUS WHILE AN UPPER RIDGE
BUILDS OVER THE WESTERN ATLANTIC. A SERIES OF UPPER DISTURBANCES IS
FORECAST TO RIPPLE THRU THE SE IN SWLY FLOW ALOFT SAT AFTERNOON INTO
SAT NIGHT.

AT THE SURFACE...A MODIFYING HIGH PRESSURE OVER THE SOUTHEAST STATES
WILL GRADUALLY SHIFT EAST THRU FRI NIGHT...YIELDING DRY WEATHER AND
WARMER TEMPS ACROSS MUCH OF THE REGION THU NIGHT THROUGH FRI NIGHT.
AS THE CENTER OF HIGH MOVES OFFSHORE BY SAT...WE WILL SEE INCREASING
GULF MOISTURE ADVECTION IN DEEP SWLY FLOW. POPS RAMP UP FROM SW TO
NE INTO THE CHANCE RANGE MAINLY ACROSS THE WESTERN HALF OF THE CWA
SAT AFTERNOON INTO THE EVENING IN LIGHT OF DEEPER MOISTURE
ASSOCIATED WITH UPPER DISTURBANCES APPROACHING FROM THE SW. TEMPS
WILL RUN 3-7 DEGREES ABOVE NORMAL THRU THE PERIOD.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 215 PM WEDNESDAY...MODELS AGREE ON ANOTHER ROUND OF UNSETTLED
WEATHER ACRS THE CWFA FOR MOST IF NOT ALL THE MEDIUM RANGE...AS A
BLOCKY PATTERN SETS UP ACRS WESTERN NORTH AMERICA. A DEEP PERSISTENT
TROF WILL SET UP ACRS THE ROCKIES/INTERMOUNTAIN WEST...WHILE AN
UPPER RIDGE LINGERS ALONG THE EAST COAST. THIS WILL PLACE THE CWFA
WITHIN A DEEP LAYER SWLY FLOW THRU THE MEDIUM RANGE. AT THE SFC...A
LARGE HIGH PRES SYSTEM WILL GRADUALLY BUILD FROM WEST TO EAST ACRS
THE GREAT LAKES...WHILE A SFC FRONT STALLS IN A SW-NE ORIENTATION
FROM THE CENTRAL GULF TO THE MID ATLANTIC STATES.

THE OP MODELS ARE IN DISAGREEMENT ON THE TIMING AND POTENCY OF A
SERIES OF SHORTWAVE/IMPULSES THAT EJECT FROM THE LONG WAVE
TROF...AND INTERACT WITH THE QUASI-STATIONARY FRONT ACRS THE
SOUTHEAST STATES. THE FIRST WAVE WILL LIKELY SPREAD A PERIOD OF
DEEPER MOISTURE AND SWLY LLVL UPGLIDE FLOW ATOP THE CWFA SATURDAY
NIGHT INTO SUNDAY. THE 00Z ECWMF HAD A STRONG SFC WAVE DEVELOP...BUT
THE 12Z RUN HAS DROP THAT SOLN...AND IS IN LINE MORE WITH THE GFS.
THE RESULT IS PERSISTENT CLOUDS AND UPGLIDE FOR SUNDAY AND MONDAY AS
WELL. POPS WILL BE LIKELY TO CATEGORICAL SATURDAY NIGHT AND
SUNDAY...TAPERING TO HIGH-CHC ON MONDAY. WE WILL BE ON THE WARM SIDE
OF THE FRONT...WITH ABOVE NORMAL TEMPS EXPECTED.

ON TUESDAY...THE SFC HIGH TO OUR NORTH FINALLY GETS FAR ENUF EAST TO
ALLOW FOR COLD AIR DAMMING TO SET UP. THIS SHUD RESULT IN COOLER
TEMPS TUESDAY. HOWEVER...THE 12Z ECMWF STILL SHOWS A BRIEF BREAK IN
THE UPGLIDE AND POPS...WITH PERHAPS SOME SUNSHINE...WEAKENING THE
CAD. THE GFS IS WETTER AND COOLER FOR TUESDAY. GIVEN THE LIKELY
CAD...I WENT WITH THE COOLER GFS GUIDANCE (CLOSE TO WPC AS WELL). ON
WEDNESDAY...THE ECWMF EJECTS THE SRN STREAM ENERGY...AND DEVELOPS A
LOW PRES SYSTEM IN THE GULF...AND TRACKS A MILLER-B SYSTEM ALONG THE
APPALACHIANS ON THURSDAY. THE GFS HOLDS THE SRN STREAM TROF/CUTOFF
LOW MUCH LONGER...AND HAS AN OHIO VALLEY LOW PRES SYSTEM TRACK FOR
FRIDAY AND SATURDAY. GIVEN THE UNCERTAINTY...WENT WITH THE SUPER
BLEND FOR WEDNESDAY...WITH JUST A SLGT CHC POP AND BELOW NORMAL
TEMPS. DESPITE THE UNSETTLED WEATHER...THERE DOES NOT LOOK TO BE
MUCH POTENTIAL FOR WINTRY PRECIP FOR OUR REGION THRU NEXT WEDNESDAY.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
AT KCLT...WITH THE WEDGE BNDRY VERY CLOSE TO THE TERMINAL...ENUF
MIXING SEEMS TO HAVE OCCURRED TO IMPROVE THE SFC VSBY BUT IT STILL
MAY TAKE UNTIL THE ARRIVAL OF THE COLD FRONT...AT SOME POINT LATER
TONIGHT...RAISE LIFR CIGS.  THE GOOD NEWS IS THAT SUNSHINE RETURNS
FOR CHRISTMAS DAY WITH WESTERLY WINDS AVERAGING 5-10 KTS.

ELSEWHERE...A COLD IS MAKING INROADS INTO THE FAR WESTERN FA THIS
EVENING WHICH WILL SCOUR LOW CIGS AND VSBY FROM WEST TO EAST THIS
EVENING. VFR ON TAP ALL DAY TOMORROW.

OUTLOOK...DRY HIGH PRESSURE WILL BUILD BACK INTO THE REGION THURSDAY
NIGHT AND FRIDAY WITH VFR CONDITIONS. ANOTHER COLD FRONT WILL ARRIVE
FROM THE NW SATURDAY NIGHT AND MAY STALL OVER THE MTNS. THAT MAY
ALLOW RESTRICTIONS TO DEVELOP BY SUNDAY MORNING...PERHAPS CONTINUING
THROUGH THE MIDDLE OF NEXT WEEK.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       MED   75%     LOW   55%     HIGH 100%     HIGH 100%
KGSP       HIGH  83%     HIGH  83%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  83%     HIGH 100%     HIGH 100%
KHKY       LOW   58%     LOW   48%     HIGH 100%     HIGH 100%
KGMU       HIGH  83%     HIGH  83%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH  83%     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...DENSE FOG ADVISORY UNTIL 8 PM EST THIS EVENING FOR NCZ035>037-
     056-057-068>072.
SC...DENSE FOG ADVISORY UNTIL 8 PM EST THIS EVENING FOR SCZ001>013-
     019.

&&

$$
SYNOPSIS...RWH
NEAR TERM...CSH/PM
SHORT TERM...JOH
LONG TERM...ARK
AVIATION...CSH/PM


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