Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 271109
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
609 AM EST FRI FEB 27 2015

.SYNOPSIS...
COLD CANADIAN HIGH PRESSURE WILL REMAIN ACROSS THE AREA THROUGH THE
WEEKEND. ABOVE NORMAL TEMPERATURES SHOULD RETURN TO THE AREA
MONDAY...BEFORE FALLING AGAIN TUESDAY IN THE WAKE OF A COLD FRONT. A
MORE SUBSTANTIAL COLD FRONT IS EXPECTED TO CROSS THE REGION DURING
MID-WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
1115 UTC UPDATE...WINDS WERE UPDATED FORM THE LATEST ADJMAV AND NAM.
POPS WERE RAISED SLIGHTLY NEAR THE TN BORDER PER RADAR TRENDS. AREAS
OF FOG WERE ADJUSTED PER SURFACE OBSERVATIONS.

AT 0330 EST FRIDAY...A BROAD UPPER TROUGH WAS OVER THE USA THIS
MORNING...WITH NEARLY ZONAL FLOW OVER THE SOUTHERN TIER OF STATES.
AN UPPER LOW WILL DIVE INTO THE WESTERN PORTION OF THE TROUGH OVER
CA TODAY AND TONIGHT.

THE MODELS VARY ON THE TIMING OF VARIOUS IMPULSES CROSSING OUR AREA
THROUGH TONIGHT. MODEL TIME HEIGHTS SUGGEST LINGERING LOW LEVEL
MOISTURE THROUGH TONIGHT...WHILE UPPER LEVEL MOISTURE DECREASES AS A
COLD FRONT OVER THE WESTERN ATLANTIC DRIFTS TO THE SE. GRADUALLY
DIMINISHING NW FLOW ALONG THE TN BORDER MAY PRODUCE SOME LIGHT SNOW
SHOWERS EARLY THIS MORNING. OTHERWISE...PRECIPITATION IS NOT
EXPECTED DUE TO A LACK OF LIFT EAST OF THE MOUNTAINS. LOW LEVEL FLOW
WILL VEER FROM NW TO N TO NE TODAY...AS HIGH PRESSURE BUILDS IN FROM
THE WEST. HIGH TEMPERATURES WILL RUN AROUND 15 DEGREES BELOW NORMAL
AS THE COOL AIR MASS BUILDS INTO THE REGION. LOW TEMPERATURES
TONIGHT WILL RUN AROUND 10 DEGREES BELOW NORMAL.

THE WINTER WX ADVISORY WILL REMAIN IN EFFECT FOR WIDESPREAD BLACK
ICE AND FREEZING FOG FOR ALL BUT OUR SOUTHERN TIER COUNTIES THIS
MORNING. AN SPS FOR PATCHY BLACK ICE WILL BE REMAIN IN EFFECT FOR
THE REMAINING ZONES.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 305 AM THURSDAY...THE SHORT TERM PERIOD WILL SEE
ESTABLISHMENT OF A HYBRID COLD AIR DAMMING EVENT...NOT CLASSICAL
DUE TO THE LOCATION OF THE PARENT HIGH ACROSS EASTERN VA/NORTHERN
NC. IN FACT...THERE WILL BE A DRY ONSET TO THE EVENT...AS THE CENTER
OF THE HIGH BUILDS FAR ENOUGH SOUTH TO SEND DRY LOW LEVEL AIR
THROUGH THE FORECAST AREA. NEVERTHELESS...SATURDAY IS EXPECTED TO BE
QUITE COOL...AS NE FLOW IS AIDED BY AN AREA OF SUBSTANTIAL MID/HIGH
LEVEL CLOUDS DEPICTED BY A MODEL CONSENSUS WITHIN THE ENTRANCE OF A
STRONG UPPER JET MAX. THEREFORE...TEMPS WILL STRUGGLE TO GET OUT OF
THE 30S IN ALL BUT SOUTHERN PIEDMONT AREAS SAT AFTERNOON.

SOUTHERLY FLOW DEVELOPING ABOVE THE COOL DOME...IN RESPONSE TO
CENTRAL CONUS HEIGHT FALLS...WILL RESULT IN QUICK TRANSPORT OF LOWER
LEVEL MOISTURE INTO THE AREA SAT NIGHT INTO EARLY SUNDAY. THERE
REMAINS TIMING DIFFERENCES REGARDING THE ARRIVAL OF THE MOISTURE AND
ASSOCIATED LIGHT PRECIP...WITH THE NAM REMAINING AS THE FASTEST
MODEL...WITH ONLY SLIGHT SUPPORT FROM THE SREF SYSTEM. IT IS ALSO
NOTEWORTHY THAT ONLY THE NAM DEPICTS MOISTURE DEEP ENOUGH TO SUPPORT
ICE NUCLEATION DURING THIS TIME...WHICH EXPLAINS ITS MORE ROBUST
QPF...WHILE THE OTHER MODELS WOULD SUGGEST MOISTURE DEEP ENOUGH TO
ONLY SUPPORT A DRIZZLE OR --RA EVENT. SUNDAY MORNING. WE HAVE OPTED
TO RUN WITH SLIGHT/LOW CHANCE POPS FOR LIGHT PRECIP/DZ BY DAYBREAK
SUNDAY. THE TIMING OF THIS WILL BE QUITE IMPORTANT...AS THERMAL
PROFILES WOULD BE SUPPORTIVE OF WINTRY PRECIP ACROSS MUCH OF THE
AREA DURING THIS TIME. DEPENDING UPON THE DEGREE OF ICE
NUCLEATION...A BRIEF PERIOD OF SNOW/SLEET WOULD BE POSSIBLE NEAR
ONSET TIME...BEFORE RAPID WARMING ALOFT WITHIN THE STRONG WAA REGIME
WOULD RESULT IN A CHANGE TO RAIN/FREEZING RAIN. THE CONCERN IS THAT
WITH THE POTENTIAL FOR RATHER STRONG HYBRID CAD...SOME LOCATIONS
COULD LOCK IN FREEZING TEMPS LONG ENOUGH TO ALLOW FOR SOME ICE
ACCRETION...ESP ALONG THE ESCARPMENT AND THE I-40 CORRIDOR IN THE
PIEDMONT. ON THE GOOD NEWS SIDE...DURATION AND COVERAGE OF PRECIP IS
STILL VERY MUCH IN DOUBT...AND IF FREEZING RAIN WERE TO DEVELOP AND
PERSIST IN SOME AREAS...THE MOUNT OF PRECIP EXPECTED WOULD KEEP THE
EVENT SOLIDLY IN THE ADVISORY CATEGORY.

TEMPS WILL GRADUALLY WARM LATE SUNDAY INTO SUNDAY NIGHT AS THE
PARENT HIGH MIGRATES OFF SHORE...AND A COLD FRONT APPROACHES FROM
THE TENN VALLEY. WHILE POPS GRADUALLY RAMP UP DURING THIS TIME...
THE MODEL CONSENSUS IS THAT THIS FRONTAL ZONE WILL BE VERY WEAKLY
FORCED...EVEN IN THE LOWER LEVELS...WHERE VEERED WESTERLY/WEAKLY
CONVERGENT FLOW IS ANTICIPATED BY LATE SUNDAY.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 325 AM...THE LARGE SCALE PATTERN CHANGE ONLY HINTED AT DURING
THE SHORT TERM WILL BE COMPLETED DURING THE MEDIUM RANGE...AS MAJOR
WESTERN CONUS HEIGHT FALLS FORCE HEIGHT RISES ACROSS THE EAST...WITH
A FAIRLY SUBSTANTIAL RIDGE ANTICIPATED ALONG THE EAST COAST BY DAY
7. HOWEVER...NEXT WEEK IS EXPECTED TO REMAIN SOMEWHAT UNSETTLED...AS
THIS PATTERN CHANGE WILL RESULT IN A QUASI-STATIONARY BAROCLINIC
ZONE LINGERING OVER THE SOUTHERN CONUS THROUGH MUCH OF THE PERIOD.
IN FACT...BY EARLY IN THE WORK WEEK...THE WESTERN TROUGH IS EXPECTED
TO MIGRATE INTO THE CENTRAL CONUS...RESULTING IN MOISTURE RETURN
OVER ANOTHER TRANSIENT/HYBRID CAD AIR MASS. THUS...POPS FOR UPGLIDE
PRECIP WILL BE IN PLACE DURING MUCH OF THE SUNDAY NIGHT THRU TUE
NIGHT PERIOD... ALTHOUGH IT CERTAINLY WILL NOT BE RAINING NON-STOP
DURING THIS TIME...AND PRECIP WILL BE MOSTLY ON THE LIGHT SIDE.

A MORE SUBSTANTIAL PRECIP EVENT IS QUITE POSSIBLE DURING MID-
WEEK...WHEN THE TROUGH AND ASSOCIATED COLD FRONT MOVE INTO THE
EASTERN STATES...INTERACTING WITH A WIDE OPEN GULF. IN FACT...
HEAVY RAINFALL MAY BECOME A CONCERN DURING THIS TIME. TEMPS WILL BE
QUITE VARIABLE DURING THE MEDIUM RANGE...WITH ABOVE TO WELL-ABOVE
NORMAL TEMPS EXPECTED DURING NON-CAD PERIODS...AND BELOW NORMAL
CONDITIONS EXPECTED ON DAYS OF TRANSIENT/HYBRID CAD. HOWEVER...
TEMPS SHOULD BE WARM ENOUGH DURING PERIODS OF PRECIPITATION TO
SUPPORT RAIN AS THE LONE P-TYPE.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
AT KCLT...MVFR VSBY IS HOLDING...DESPITE LOW RESTRICTIONS TO THE
EAST. VSBY SHOULD IMPROVE BY MID MORNING. THE CIT WILL REFLECT THE
MODEL TIME HEIGHT PREFERENCE FOR LOW VFR THROUGH MUCH OF THE NEXT 24
HOURS...ALTHOUGH BREAKS WILL BE POSSIBLE FROM TIME TO TIME. WINDS
WILL VEER N AND THEN NE TODAY AS HIGH PRESSURE BUILDS IN FROM THE
NW. WITH DRY LOW LEVEL SATURDAY MORNING...A VSBY RESTRICTION IS NOT
EXPECTED.

ELSEWHERE...TAF SITES REMAIN IN GOOD SHAPE...WITH MVFR CIGS AT KGSP
AND KGMU...MVFR CIGS AT KAVL AND KAND....AND NO CIG AT KHKY. VFR
VSBYS PREVAIL...DESPITE SOME LOW RESTRICTIONS TO THE EAST. SNOW
SHOWERS NW OF KAVL ARE NOT EXPECTED TO REACH THE FIELD...AND SHOULD
DIMINISH BY MIDDAY. MODEL TIME HEIGHTS SUGGEST LOW VFR CIGS FOR MUCH
OF THE NEXT 24 HOURS...EXCEPT HIGH END MVFR AT KAVL...HOWEVER DRYING
FROM ALOFT MAY INTRODUCE BREAKS FOR MUCH OF THE PERIOD. WINDS WILL
VEER FROM N TO NE TODAY...EXCEPT AT KAVL WHERE THEY WILL REMAIN FROM
THE N UNTIL LATE THIS EVENING...WHEN THEY VEER SE. DRY LOW LEVEL
WILL PRECLUDE VSBY RESTRICTIONS SATURDAY MORNING.

OUTLOOK...LOW LEVEL MOISTURE WILL LINGER THROUGH THE REMAINDER OF
THE WEEK AND INTO THE WEEKEND AS COLD AIR DAMMING BUILDS FROM
THE NORTH ON SATURDAY. FLIGHT RESTRICTIONS WILL BE POSSIBLE DURING
THIS TIMEFRAME...ESPECIALLY ON SUNDAY ONCE MOISTURE SPREADS IN FROM
THE SOUTH AND CIGS LOWER.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     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...WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
     GAZ010-017-018.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ033-
     048>053-058-059-062>065-501-503-505-507-509.
     WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
     NCZ035>037-056-057-068>072-082-502-504-506-508-510.
SC...WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
     SCZ001>009.

&&

$$
SYNOPSIS...JDL
NEAR TERM...JAT
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JAT



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