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Area Forecast Discussion

197
FXUS62 KGSP 010947
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
547 AM EDT SAT NOV 1 2014

.SYNOPSIS...
A DEEP UPPER LOW PRESSURE SYSTEM WILL CROSS THE AREA FROM THE
WEST TODAY. THIS SYSTEM WILL BE ACCOMPANIED BY COLD TEMPERATURES
AND VERY WINDY CONDITIONS. DRY AND COLD HIGH PRESSURE WILL RETURN
SUNDAY THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 5 AM...AN AREA OF LIGHT TO MODERATE PRECIP CONTINUES TO PIVOT
ACROSS UPSTATE SC AS THE UPPER LOW MOVES DOWN ACROSS THE SRN
APPALACHIANS. AS EARLIER FEARED...PRECIPITATION RATE HAS BEEN HIGH
ENOUGH IN SOME OF THE GREENVILLE METRO AREA TO BRING THE FREEZING
LEVEL DOWN VERY CLOSE TO THE SFC...IN PARTICULAR THE AREA FROM THE
WEST SIDE OF GREENVILLE THROUGH TRAVELERS REST AND NEAR PARIS MTN.
PRECIPITATION WILL FALL AS A MIX OF RAIN AND WET SNOW ACROSS MUCH OF
THE UPSTATE...WITH A FEW POCKETS WHERE IT CHANGES TO ALL WET SNOW.
MOST OF THE ACCUMULATION WILL BE ON GRASSY AND ELEVATED SURFACES. AS
IT STANDS RIGHT NOW...THE AREA WHERE SNOW IS LIKELY TO ACCUMULATE
WILL BE VERY LOCALIZED TO A SMALL PART OF NORTHERN GREENVILLE
COUNTY...SO IT WILL BE HANDLED WITH A SPECIAL WEATHER STATEMENT.
FORTUNATELY...MOST OF THE SNOW WILL MELT ON CONTACT WITH ROAD
SURFACES. THIS REMAINS A DYNAMIC SITUATION SO ADDITIONAL UPDATES ARE
POSSIBLE. IF TEMPS DROP ANOTHER DEGREE OR TWO...THE WINTER WX
ADVISORY WILL BE EXPANDED TO INCLUDE THE GSP METRO AREA. THE
CATEGORICAL POP WAS EXPANDED AND EXTENDED ACROSS THE UPSTATE TO
HANDLE THIS DEVELOPMENT.

THE UPPER LOW SHOULD PASS OVERHEAD THROUGH THE MORNING HOURS WITH
ALL MANNER OF LOW/MID/HIGH UPPER FORCING COMING INTO PLAY. HAVE
RAISED/EXPANDED THE PRECIP PROBABILITY THROUGH THE MORNING HOURS.
CANNOT RULE OUT A CHANGEOVER TO WET SNOW ACROSS THE NC
FOOTHILLS/UPSTATE AS THE COLDER AIR SPILLS DOWN FROM THE MTNS. A
MIX/CHANGEOVER ACTUALLY APPEARS A BIT LESS OF A POSSIBILITY OVER
METRO CLT AS THE MODEL TREND WAS A BIT WARMER THIS MORNING.
HOWEVER...AS WE ARE SEEING CURRENTLY OVER GSP...IF THE PRECIPITATION
FALLS WITH ENUF INTENSITY...SOME WET SNOW COULD MAKE IT TO THE
GROUND. THE UPPER LOW SHOULD PULL A QUICK EXIT OFF TO THE EAST
DURING THE MIDDLE PART OF THE DAY...BRINGING THE LOW LEVEL WINDS
AROUND TO A N TO NW DOWNSLOPE AFTER 15Z...WHICH SHOULD START TO
DIMINISH PRECIP POTENTIAL NEAR THE BLUE RIDGE/WRN UPSTATE. AS THE
LOW MOVES AWAY...SOME WRAP AROUND DEFORMATION MAY LINGER OVER THE
WRN PIEDMONT INTO THE AFTERNOON...BUT THAT SHOULD ALSO DIE OFF AND
MOVE EAST BY LATE AFTERNOON. MEANWHILE...THE MTNS WILL UNDERGO A
TRANSITION TO A MORE PURE NW FLOW PRECIP EVENT...WHICH WILL MAINLY
BE SNOW. WILL MAINTAIN A HIGH PRECIP CHANCE NEAR THE TN BORDER...AND
TAPER IT OFF EASTWARD FROM THERE.

WE SHOULD CONTINUE TO DRY OUT EVERYWHERE E OF THE SPINE OF THE
APPALACHIANS THIS EVENING AND TONIGHT. HOWEVER...THE NW FLOW SNOW
WILL CONTINUE INTO TONIGHT ALONG THE TN BORDER. THIS MAY REQUIRE
EXTENDING THE WINTER STORM WARNING THROUGH THIS EVENING. WIND GUSTS
SHOULD ABATE ENUF AROUND SUNSET THAT WE CAN KEEP THE SAME EXPIRATION
TIME ON THE WIND ADVISORY. AS FOR THE FREEZE WATCH...FCST LOWS ARE
SUCH THAT WE CAN ROLL THAT OVER TO A FREEZE WARNING. THE WARNING
WILL HAVE TO BE EXPANDED INTO THE NRN FOOTHILLS OF NC BASED ON THE
MIN TEMP FCST. HENDERSON COUNTY NC WILL BE LEFT OUT AS THE FROST/
FREEZE PROGRAM ENDS 1 NOVEMBER AS A MATTER OF POLICY.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 300 AM EDT SAT...A DEEP UPPER LOW PRESSURE TROUGH OFF THE
CAROLINAS COAST 12Z SUN WILL LIFT NNE INTO THE MAINE COAST BY 00Z
MON...LEAVING THE CWA UNDER NWLY FLOW ALOFT ON SUN. H5
HEIGHTS/THICKNESSES RISE CONSIDERABLY BY MON AS AN UPPER RIDGE
BUILDS IN FROM THE WEST. THE UPPER RIDGE AXIS IS FORECAST TO REACH
OUR REGION BY MON NIGHT.

AT THE SURFACE...1030MB SURFACE HIGH WILL BUILD IN FROM THE NW SUN
AND BECOMES CENTERED OVER THE SE STATES BY MONDAY. ANY LINGERING NW
PRECIP ALONG THE TN BORDER LINE SHOULD TAPER OFF BY SUN MORNING AS
DRY AIRMASS MOVES IN. WITH PREVAILING CAA NW FLOW ON SUN...TEMPS
SHOULD REMAIN AROUND 10-15 DEGREES BELOW NORMAL. LATEST GUIDANCE
SUGGESTS THAT SUB-FREEZING TEMPS ARE EXPECTED OVER MUCH OF
THE CWA ON SUN NIGHT. THEREFORE...ANOTHER FREEZE WATCH MAY BE NEEDED
OVER EAST OF THE MTNS FOR THIS PERIOD.

AS MODIFYING HIGH PRESSURE CENTERED OVER THE REGION SHIFTS EAST
THROUGH MONDAY NIGHT...WINDS WILL VEER TO THE SW AND TEMPS SHOULD
WARM UP BY MORE THAN 10 DEGREES BY MON AFTERNOON IN ITS WAKE.
CONDITIONS SHOULD REMAIN DRY UNDER THE HIGH PRESSURE MON.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 230 AM EDT SAT...LATEST GLOBAL MODELS CONTINUE TO AGREE
THAT AN UPPER RIDGE AXIS OVER THE EASTERN STATES WILL SHIFT
OFFSHORE BY TUE NIGHT AS A POSITIVELY TILTED UPPER TROUGH
APPROACHES FROM THE CENTRAL CONUS. THIS TROUGH IS FORECAST TO
CROSS THE EASTERN CONUS BETWEEN WED NIGHT AND THU...OFF THE
ATLANTIC COAST BY EARLY FRI.

AT THE SURFACE...A MODIFYING HIGH PRESSURE CENTERED OVER THE SE
STATES WILL GRADUALLY SHIFT OFFSHORE TUE INTO WED AS A WEAK COLD
FRONT APPROACHES FROM THE WEST. THE FRONT SHOULD CROSS THE REGION
LATE WED INTO THU...OFF TO OUR EAST BY THU NIGHT. IT STILL APPEARS
THAT THE FRONT WILL BE MOISTURE STARVED. HENCE...HAVE INHERITED
SLIGHT CHANCE POPS OVER THE PIEDMONT WITH LOW END CHANCE MANLY OVER
THE WESTERN ZONES OF THE MTNS WED AFTERNOON THRU THU MORNING.
CONDITIONS LOOK DRY THU NIGHT AND FRI AS A COOL HIGH PRESSURE BUILDS
IN FROM THE WEST. MODES SUGGEST THAT THERE COULD BE LIGHT NW PRECIP
(A MIX OF RAIN AND SNOW) BEHIND THE DEPARTING FRONT ALONG THE TN
BORDER THU NIGHT INTO FRI. SO HAVE KEPT SLIGHT CHANCE FOR RN/SN
THERE THRU FRI MORNING. TEMPS SHOULD START OUT AROUND 3-5 DEGREES
BELOW NORMAL TUE...WARMING UP TO NEAR NORMAL BY WED. TEMPS THEN COOL
OFF BY 5-7 DEGREES BY FRI IN THE WAKE OF THE FROPA.

&&

.AVIATION /10Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...ADDITIONAL AREAS OF LIGHT RAIN HAVE DEVELOPED ACROSS THE
NRN UPSTATE OF SC AND INTO THE CLT METRO AREA. EXPECT LIGHT RAIN TO
CONTINUE FALLING FOR THE BETTER PART OF THE PRE-DAWN HOURS...WHICH
IS EXPECTED TO BRING THE CEILING DOWN INTO THE MVFR RANGE NO LATER
THAN 10Z. WIND WILL REMAIN N AND WILL STRENGTHEN THROUGHOUT THE
MORNING...BECOMING GUSTY ONCE THE SUN RISES AND THE BOUNDARY LAYER
DEEPENS ENUF TO TAP INTO SOME HIGHER WIND ALOFT. THE BIG QUESTION
THIS MORNING IS THE PRECIP TYPE. THE MODEL TREND ON THE 00Z RUN WAS
FOR A SLIGHTLY WARMER AND DEEPER BOUNDARY LAYER. FCST SOUNDINGS NO
LONGER SUPPORT SNOW. SFC TEMPS DO NOT FALL BELOW ABOUT 39 DEGREES
EVEN ON THE COLDEST MODEL GUIDANCE. FOR THAT REASON...HAVE
ELIMINATED THE RAIN SNOW MIX THAT WAS IN THE PREVIOUS TAF. WILL
NEVER COMPLETELY RULE OUT SOME WET SNOWFLAKES OR SLEET PELLETS IN
THIS TYPE OF SITUATION WITH A VERY DYNAMIC AND COLD CORE UPPER
LOW...BUT THE CHANCE IS ONLY SOMETHING LIKE 10 PERCENT...SO IT WAS
LEFT OUT OF THE 06Z TAF. WILL EVALUATE AGAIN WHEN THE 03Z SREF
GUIDANCE ARRIVES...AND THE REST OF THE FCST IS UPDATED. THE UPPER
LOW MOVES OUT QUICK DURING THE MIDDLE PART OF THE DAY. CEILING
SHOULD START TO IMPROVE AROUND 17Z AND SHOULD LIFT TO VFR BY MID
AFTERNOON. THE LOW CLOUDS MAY SCATTER OUT QUICKER THAN THE TAF
INDICATES...BUT CERTAINLY BY AROUND SUNSET...AT WHICH TIME THE WIND
GUSTS SHOULD SUBSIDE.

ELSEWHERE...KAVL WILL HAVE THE GREATEST IMPACT. ANY PRECIP THAT
FALLS SHOULD MAINLY BE IN THE FORM OF SNOW AT KAVL...AND SHOULD
BRIEFLY REDUCE VSBY TO MVFR OR IFR RANGE. WENT WITH A TEMPO IFR FOR
THE SNOW FOR THE FIRST PART OF THE TAF BASED ON RADAR TREND... AND
THIS WILL PROBABLY BE MOVED FORWARD IN TIME WITH EACH SUCCESSIVE
AMEND. THE OTHER TAF SITES SHOULD SEE LIGHT RAIN AS COLDER AIR
FILTERS IN...PERHAPS MIXING WITH SOME WET SNOW FROM AROUND DAYBREAK
TO MID MORNING DURING THE MOST DYNAMIC PART OF THE LOW PASSAGE. THIS
WAS INCLUDED AS A TEMPO AT KHKY/KGSP/KGMU...BUT LEFT OUT OF KAND AS
DOWNSLOPE SHOULD SUPPRESS PRECIP AROUND THE SAV RIVER BASIN. THE LOW
CLOUDS AND PRECIP WILL PERSIST THROUGH THE DAY AT KAVL...BUT MOVE
OUT E OF THE MTNS AROUND MIDDAY.

OUTLOOK...DRYING HIGH PRESSURE WILL BUILD IN LATE THIS WEEKEND AND
CONTINUE THROUGH EARLY NEXT WEEK...BRINGING VFR CONDITIONS.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR GAZ010-
     017.
     WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR GAZ010-017.
     FREEZE WARNING FROM MIDNIGHT EDT TONIGHT TO 9 AM EST SUNDAY
     FOR GAZ010-017-018-026-028-029.
     FREEZE WARNING UNTIL 10 AM EDT THIS MORNING FOR GAZ010.
NC...WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NCZ053-
     059-062>065-501-503-505-507-509.
     WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NCZ033-035-
     048>053-058-059-062>065-501>510.
     FREEZE WARNING FROM MIDNIGHT EDT TONIGHT TO 9 AM EST SUNDAY
     FOR NCZ035-056-068-069-501>510.
     WINTER STORM WARNING UNTIL 8 PM EDT THIS EVENING FOR NCZ033-
     048>052-058.
     FREEZE WARNING UNTIL 10 AM EDT THIS MORNING FOR NCZ033-049-050-
     053-063>065.
SC...WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ003.
     WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR SCZ001>003.
     FREEZE WARNING FROM MIDNIGHT EDT TONIGHT TO 9 AM EST SUNDAY
     FOR SCZ001>008-010>013-019.

&&

$$
SYNOPSIS...JOH
NEAR TERM...PM
SHORT TERM...JOH
LONG TERM...JOH
AVIATION...PM



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