Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 282359
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
659 PM EST SUN DEC 28 2014

.SYNOPSIS...
A COLD FRONT WILL SLOWLY CROSS OUR REGION THROUGH MONDAY...THOUGH
SOME MOISTURE WILL LINGER UNTIL TUESDAY. DRIER AND COOLER HIGH
PRESSURE WILL MOVE ACROSS THE AREA WEDNESDAY AND THURSDAY. ANOTHER
LOW PRESSURE SYSTEM THEN SHOULD BEGIN TO TAKE SHAPE AT THE END OF
THE WEEK...BRINGING PRECIPITATION BACK TO THE AREA BY FRIDAY.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 700 PM...NO SIGNIFICANT CHANGES WITH THIS UPDATE. UPDATED THE
AVIATION GRIDS FOR THE 00Z TAFS.

AS OF 430 PM...MADE A QUICK UPDATE TO THE SKY/POP/WX GRIDS TO MATCH
UP WITH THE TRENDS. IT LOOKS LIKE A FEW BREAKS IN THE CLOUDS ACRS
THE MTNS AND ADJACENT FOOTHILLS...WHILE THERE IS VERY LITTLE IN THE
WAY OF RADAR ECHOES ON THE KGSP OR KMRX RADARS. SO HAVE BUMPED BACK
POP FOR THE REST OF THE AFTN INTO EARLY EVENING.
OTHERWISE...TEMPS/DEWPTS/WINDS LOOK GOOD.

AS OF 230 PM EST SUNDAY...A WEAK SURFACE COLD FRONT WAS MOVING
ACROSS THE NC MTNS ZONES AS OF THIS AFTERNOON HOURS. THIS FRONT WILL
SLOWLY CROSS THE REST OF THE CWA THROUGH THE EVENING AND OFF TO OUR
SE BY LATE TONIGHT. DESPITE THE FROPA...A LULL IN PRECIP IS EXPECTED
MAINLY EAST OF THE MTNS THIS AFTERNOON THRU THE EVENING IN LIGHT OF
THE OCCURRENCE OF NEGATIVE VORTICITY ADVECTION AND WEAKENING
ISENTROPIC UPGLIDE. HENCE...HAVE KEPT 20/30 POPS FOR LIGHT RAIN OR
DRIZZLE OVER THE PIEDMONT THRU THE EVENING. POPS THEN RAMP UP FROM
NW TO SE THROUGH TONIGHT AS A BAND OF PRECIP ASSOCIATED WITH A LINE
OF UPPER VORT MAX AHEAD OF THE APPROACHING UPPER TROUGH AXIS PUSHES
THROUGH THE AREA. LATEST SHORT RANGE MODELS CONTINUE TO INDICATE
THAT A WEAK CYCLOGENESIS WILL TAKE PLACE ALONG A BAROCLINIC ZONE
ACROSS NE GA AND THE CAROLINAS LATE TONIGHT INTO MON MORNING. THIS
WILL SUPPORT ANOTHER ROUND OF RAIN...WITH POPS FURTHER RAMPING UP
INTO THE 70/80 PERCENT RANGE BETWEEN 6Z AND 12Z MON. IN RESPONSE TO
THIS...BOTH 12 THE GFS AND THE ECMWF SHOW 0.25-0.5" QPF OVER MUCH OF
THE AREA DURING THIS PERIOD. HOWEVER...THE 12Z NAM IS A DRY OUTLIER
AMONG THE MODELS...SHOWING LESS THAN A TENTH OF AN INCH. SO HAVE
LEANED TOWARD THE HPC QPF GUIDANCE WHICH IS SIMILAR TO THE
GFS/ECMWF...FEATURING 0.25-05" QPF TONIGHT THRU MON MORNING. POPS
RAMP DOWN THROUGH MON AFTERNOON...BUT KEPT IN THE CHANCE RANGE AS
THE WAVE OF LOW EXITS NE AND AND A WEAK COLD AIR WEDGE SETS UP OVER
THE AREA...MAINTAINING SOME DEGREES OF ISENTROPIC UPGLIDE OVERHEAD.
TEMPERATURES WILL REMAIN 3-5 DEGREES ABOVE NORMAL THRU THE PERIOD.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 AM SUNDAY...THE MODELS CONTINUE TO SHOW EXTENSIVE LOW
LEVEL MOISTURE HANGING BACK ACROSS THE WESTERN CAROLINAS AND NE
GEORGIA MONDAY NIGHT AND INTO TUESDAY MORNING AS A LIGHT S/SE FLOW
DEVELOPS IN RESPONSE TO A MID LEVEL WAVE MOVING OVER THE MIDWEST.
THE NAM IN PARTICULAR DEVELOPS AN UPSLOPE FLOW OVER THE NC BLUE
RIDGE WHICH FORCES CONTINUED LIGHT PRECIP IN THAT AREA...THOUGH THE
GFS DOES NOT APPEAR AS STRONG. BOTH MODELS SUGGEST THE SURFACE HIGH
WELL TO THE WEST WILL SPILL OVER THE CENTRAL APPALACHIANS AND SET UP
A WEAK WEDGE OF SORTS BY TUESDAY SUNRISE. THE LIGHT FLOW OVER THE
TOP OF THIS SORT-OF WEDGE SHOWS UP AS ISENTROPIC LIFT PARTICULARLY
ON THE NAM...WHICH HELPS TO DEVELOP PRECIP OVER AT LEAST THE NC PART
OF THE FCST AREA MONDAY NIGHT AND INTO TUESDAY MORNING AS THE WEDGE
BOUNDARY DROPS S. FORTUNATELY...PARTIAL THICKNESS REMAINS FAIRLY
HIGH UNTIL TUESDAY AFTERNOON WHEN THE COLDER AIR FINALLY STARTS TO
MOVE IN FROM THE NW...SO PRECIP SHOULD BE IN FORM OF LIGHT RAIN OR
DRIZZLE ACROSS ALL BUT THE VERY HIGHEST RIDGETOPS. THINK PRECIP WILL
BE LIGHT AS THE BETTER FORCING REMAINS OVER THE MID-ATLANTIC THRU
TUESDAY. THERE COULD BE A CHANGEOVER TO SNOW SHOWERS ON THE TN
BORDER LATE TUESDAY AND TUESDAY EVENING AS THE FLOW COMES AROUND
MORE NW AND FORCES SOME UPSLOPE DEVELOPMENT AS THE COLD AIR COMES
IN. E OF THE MTNS...THE PRECIP SHOULD EXIT BEFORE THE COLD AIR
ARRIVES. THE REST OF TUESDAY NIGHT AND WEDNESDAY SHOULD BE FAIR AS
WE SHOULD BE UNDER THE NEARLY ZONAL FLOW IN THE CONFLUENT PART OF
THE OVERALL SPLIT FLOW UPPER PATTERN...WHICH WILL SUPPORT HIGH
PRESSURE AT THE SURFACE RIDGING IN FROM THE WEST.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 245 PM SUNDAY...ON THURSDAY...MID LEVEL FLOW ACROSS THE
FORECAST AREA WILL REMAIN ZONAL AS A DEEP CLOSED LOW ROTATES ACROSS
THE FOUR CORNERS AREA. AT THE SFC...LARGE HIGH PRESSURE CENTERED
OVER THE LOWER MISSISSIPPI RIVER VALLEY WILL BEGIN TO BUILD EAST
ACROSS THE CAROLINAS. CONDITIONS WILL REMAIN DRY WITH LIGHT WINDS
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT. A BLEND OF TEMPERATURE
GUIDANCE INDICATES THE TEMPERATURES WILL RANGE CLOSE TO NORMALS.
THURSDAY AND FRIDAY MORNING LOWS ARE FORECAST TO RANGE FROM THE MID
20S TO AROUND 30...RISING TO THE MID 40S TO AROUND 50S THURSDAY
AFTERNOON.

ON FRIDAY...THE CLOSED MID LEVEL LOW IS EXPECTED TO TRACK SE ACROSS
THE DESERT SW...NEARING THE WEST TX BORDER BY FRIDAY EVENING.
CIRCULATION AROUND THE DEEP LOW SHOULD RESULT IN BROAD WARM AIR
ADVECTION ACROSS SOUTHERN PLAINS TO DEEP SOUTH. MOISTURE SHOULD
STREAM ACROSS THE SOUTHERN APPALACHIAN REGION DURING THE
DAY...INCREASING FROM THE TOP DOWN. BASED ON THE LATEST
GUIDANCE...I WILL DELAY THE ARRIVAL OF CHC POPS UNTIL AFTER SUNRISE
FRIDAY. BY FRIDAY AFTERNOON...THE COMBINATION OF INCREASING MOISTURE
AND DEEPENING FORCING SHOULD SUPPORT CHC POPS...ESPECIALLY ACROSS
THE MTNS. TEMPERATURES WILL REMAIN SLIGHTLY BELOW NORMAL ON FRIDAY.
BASED ON THE PRECIP TIMING AND TEMPERATURE FORECAST...MORNING FZRA
IS POSSIBLE ACROSS THE MTNS...RESULTING IN LITTLE TO NO
ACCUMULATIONS. GENERALLY...PRECIP WILL FALL AS A CHILLY RAIN.

SATURDAY AND SUNDAY...THE CLOSED LOW IS EXPECT TO TRACK NE ACROSS
THE MID MISSISSIPPI AND OHIO RIVER VALLEYS...WEAKENING DURING ITS
TREK. MODELS INDICATE THAT THE REGION WILL REMAIN UNDER A DEEP PLUME
OF MOISTURE THROUGH THE WEEKEND. FORCING WILL BE LARGELY GENERATED
BY LLVL ISENTROPIC LIFT AND UPSLOPE FLOW. BY SUNDAY...THE ASSOCIATED
COLD FRONT WILL SWEEP EAST OVER THE WESTERN CAROLINAS AND NE GA.
GUIDANCE INDICATES THAT WEAK CAPE AND UPPER JET DIVERENGE MAY
SUPPORT A FEW TSRA SUN AFTERNOON. I WILL HIGHLIGHT THE PRECIP
POTENTIAL WITH LIKELY TO CHC POPS. THE GFS INDICATES THAT A
SECONDARY FRONTAL WAVE WILL DEVELOP NEAR THE MISSISSIPPI DELTA LATER
ON SUNDAY...KEEPING THE CWA UNDER A STATIONARY FRONT. THE ECMWF IS
MUCH DRIER AND PUSHES THE COLD FRONT EAST DURING THE DAY ON SUNDAY.
I WILL TAKE A COMPROMISE OF BOTH SOLUTIONS AND HOLD ONTO CHC TO SCHC
POPS THROUGH DAY7.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
AT KCLT...A CHALLENGING 00Z TAF...WITH A WEAK COLD FRONT SAGGING
SOUTHWARD ACRS THE NC PIEDMONT THIS EVENING. ALOFT...A WNWLY FLOW
HAS HELPED CLEAR OUT THE LOW STRATUS. GUIDANCE NOT HANDLING THIS
CLEARING WELL...WITH MAJORITY SAYING IT SHUD BE IFR. THE FRONT WILL
MAKE SLOW PROGRESS SOUTH OVERNIGHT...AS LLVL UPGLIDE RAMPS UP ATOP
THE FRONTAL ZONE. A BRIEF PERIOD OF DEEPER MOISTURE AND MID-UPR
FORCING SHUD BRING A RAIN SHIELD ACRS THE AREA LATE TONIGHT THRU
MONDAY MORNING. CIGS AND VSBY WILL LIKELY GO IFR WITHIN PRECIP.
PRECIP WILL TAPER OFF BY MIDDAY...BUT LLVL CLOUDS AND MOISTURE WILL
PERSIST THRU THE DAY WITH ONLY SLIGHT IMPROVEMENT IN CONDITIONS.
WINDS WILL BE LIGHT THRU THE PERIOD...FAVORING A N TO NE DIRECTION
BEHIND THE FRONT...WHICH SHUD PUSH THRU BY 4-5Z.

ELSEWHERE...AS WITH KCLT...CONFIDENCE IS LOW. KAVL AND KHKY ARE
STARTING OUT VFR...WITH A DRYING WLY DOWNSLOPE FLOW. ACRS THE
UPSTATE...THE FLOW IS WEAKER AND MOISTURE SEEMS TO BE HOLDING TOUGH.
THERE IS A CHANCE THAT SOME CLEARING WILL OCCUR ACRS THE UPSTATE.
HOWEVER...THE VAST MAJORITY OF GUIDANCE KEEPS THINGS IFR THRU THIS
EVENING. I WILL GO WITH THE IFR...SINCE THAT WAS IN THERE...AND CIGS
HAVE SHOWN NO IMPROVEMENT SO FAR IN THE METARS. OVERNIGHT...A PRECIP
SHIELD IS EXPECTED TO CROSS THE AREA...WITH MVFR TO IFR CIGS/VSBY
EXPECTED BY DAYBREAK MONDAY. THE PRECIP WILL TAPER OFF/SHIFT EAST BY
MIDDAY MONDAY...HOWEVER...LOW CIGS AND VSBY WILL PERSIST THRU THE
DAY. WINDS WILL BE GENERALLY LIGHT SW UNTIL THE SFC FRONT PUSHES
THRU FROM THE NORTH AROUND 4-5Z...THEN WINDS WILL FAVOR A N/NE
DIRECTION. NLY WINDS EXPECTED AT KAVL THRU THE PERIOD.
A BRIEF PERIOD OF VFR/MVFR CIGS EARLY THIS AFTERNOON IN
RESPONSE TO INCREASING SW WINDS AHEAD OF AN APPROACHING SURFACE COLD
FRONT WILL QUICKLY GIVE WAY TO IFR CIGS...AS LATEST VISBY SATELLITE
SHOWS CONSIDERABLE IFR CLOUDS SPREADING BACK IN FROM THE SW. LATEST
GUIDANCE IS SUPPORTIVE OF LIFR CIGS THIS EVENING THRU THE END OF
THE TAF PERIOD. HENCE...HAVE MENTIONED 200-400FT RANGE CIGS BEYOND
22Z...CONTINUING THRU 18Z MON. SW WINDS WILL VEER TO THE NORTH AS
THE FRONT PUSHES THRU TONIGHT. AS A WAVE OF SURFACE LOW SETS UP OVER
THE WESTERN CAROLINAS...PRECIP WILL SPREAD OVER THE REGION AND WINDS
WILL VEER MORE TO THE NE BY MON MORNING. AREAS OF FOG WITH IFR
VISBY WILL AFFECT THE TERMINAL TONIGHT AND TOMORROW AS LLVL COOL AND
MOIST AIRMASS SPREADS FROM THE NE UNDERNEATH THE PERSISTING WAA SWLY
FLOW ALOFT.

ELSEWHERE...BKN TO SCT VISBY/MVFR CLOUDS CURRENTLY OVER THE NC MTNS
AND PORTIONS OF THE WESTERN NC PIEDMONT WILL GIVE WAY TO OVC IFR
CLOUDS BY LATE THIS AFTERNOON/EVENING AS A BAND OF PRECIP
ASSOCIATED WITH AN UPPER TROUGH AXIS PUSHES THRU THE AREA. ELSEWHERE
WILL SEE CONTINUED IFR CONDITIONS THRU THE PERIOD. AREAS OF FOG WITH
IFR VISBY WILL DEVELOP ACROSS MUCH OF THE REGION TONIGHT...MOIST AND
COOLER AIRMASS SPREADS IN FROM THE NE BEHIND THE DEPARTING COLD
FRONT. WITH A WAVE OF SURFACE LOW SETS UP ACROSS THE WESTERN
CAROLINAS BY EARLY MON...LIFR CLOUDS AND AREAS OF PRECIP WILL AFFECT
THE MOST LOCATIONS IN ITS WAKE. S/SW WINDS WILL VEER TO THE N
TONIGHT WITH THE FROPA...AND VEER TO THE NE BY MON MORNING.

OUTLOOK...PERIODS OF LIGHT RAIN AND FLIGHT RESTRICTIONS MAY LINGER
MONDAY AND MONDAY NIGHT BEFORE GRADUAL IMPROVEMENT OCCURS THROUGHOUT
TUESDAY. DRY HIGH PRESSURE SHOULD RETURN BY MID-WEEK.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH  94%     MED   76%     HIGH  85%     MED   62%
KGSP       HIGH  84%     HIGH  80%     MED   68%     HIGH  93%
KAVL       HIGH  86%     HIGH  80%     MED   77%     HIGH 100%
KHKY       HIGH  84%     HIGH  83%     HIGH  83%     HIGH  84%
KGMU       HIGH  86%     HIGH  86%     MED   75%     MED   75%
KAND       HIGH  84%     HIGH  83%     MED   70%     MED   78%

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...DEO
NEAR TERM...ARK/JOH
SHORT TERM...PM
LONG TERM...ARK/NED
AVIATION...ARK



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