Winter Storm Watch 3, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
434 AM EDT SUN OCT 28 2012

.SYNOPSIS...
TROPICAL CYCLONE SANDY WILL CONTINUE TO MOVE NORTH ALONG THE EAST
COAST THROUGH THE WEEKEND. BY MONDAY SANDY WILL DEVELOP INTO A
POWERFUL NOR-EASTER. THE STORM IS EXPECTED TO CURVE WEST AND MOVE
ASHORE NEAR NEW JERSEY MONDAY NIGHT. THIS WILL RESULT IN
UNSEASONABLY CHILLY AND WINDY CONDITIONS OVER THE AREA WITH SNOW AND
FREEZING TEMPERATURES IN THE MOUNTAINS.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 430 AM EDT...CIRRUS SHIELD ASSOCIATED WITH SANDY WILL REMAIN
RATHER THICK ACROSS THE CWA THROUGH THIS AFTERNOON. THE ECMWF
INDICATE THAT QG FORCING WILL INCREASE ACROSS THE WESTERN CAROLINAS
THIS AFTERNOON WITH THE APPROACH OF H5 TROF OVER THE UPPER
MISSISSIPPI RIVER VALLEY. THE COMBINATION OF THE INCREASING LIFT AND
LLVL MOISTURE SHOULD SUPPORT THE FORMATION OF A THICK LAYER OF
CLOUDS BETWEEN 050 TO 100 KFT THIS AFTERNOON. OVER THE MTNS...THE
COMBINATION OF INCREASING NW FLOW AND INCREASING SYNOPTIC SCALE
FORCING SHOULD YIELD AN INCREASING AREA OF SHRAS...ESPECIALLY NEAR
THE TN BORDER. THE CONSENSUS OF THE NEAR TERM GUIDANCE INDICATES
THAT COVERAGE MAY RANGE FROM CATE ACROSS THE WEST FACING SLOPES OF
THE NRN MTNS TO SCHC ACROSS THE FOOTHILLS. QPF AMOUNTS WILL ALSO
RANGE FROM OVER .3 OF AN INCH ALONG THE TN LINE TO A FEW HUNDREDTHS
ACROSS THE FOOTHILLS. TEMPERATURES WILL LIKELY PEAK DURING THE EARLY
AFTERNOON...THEN A GRADUAL COOLING TREND IS EXPECTED THROUGH THE
REMAINDER OF THE AFTERNOON. HIGH TEMPERATURES ARE FORECAST TO RANGE
FROM THE L50S ACROSS THE MTN VALLEYS TO THE MID 40S ACROSS THE HIGH
TERRAIN...HIGHS MAY RANGE IN THE L70S EAST OF I-85. GUSTY NNW WINDS
WILL DEVELOP DURING THE MID MORNING PERIOD...WITH GUSTS INCREASING
GRADUALLY TO 25 TO 30 MPH DURING THE AFTERNOON HOURS.

THIS EVENING AND TONIGHT...H85 CAA WILL DROP TEMPS ACROSS THE MTNS
FROM 0C OVER THE ESCAPEMENT TO -5C OVER THE BLUE RIDGE. GIVEN THE
SHARP CAA...I WILL FAVOR THE 2M TEMPS FROM THE NAM12 OVER THE MOS.
TAKING THIS APPROACH...MIN TEMPERATURES ARE EXPECTED TO RANGE FROM
THE U20S ACROSS THE HIGH TERRAIN TO THE L30S WITHIN THE MTN VALLEYS.
FOOTHILL AND PIEDMONT AREAS WILL COOL TO THE LOW 40S. WE WILL ISSUE
A FREEZE WARNING FOR THE NC MTNS AND RABUN COUNTY FOR TONIGHT...THIS
FREEZE WILL LIKELY END THE GROWING SEASON.

DURING THE PRE DAWN HOURS ON MON...THE PRESSURE GRADIENT IS EXPECTED
TO RANGE FROM 6 TO 9 MBS ACROSS THE NC MTNS. IN ADDITION...CAA
SHOULD SUPPORT A MIXED LAYER BETWEEN 1 TO 2 KFT OVERNIGHT. WINDS ARE
EXPECTED TO RANGE FROM 20 TO 25 KTS WITH GUSTS BETWEEN 40 TO 50
KTS...ESPECIALLY ACROSS THE HIGH TERRAIN. IN ADDITION...NW FLOW AND
PERIOD OF UPPER FORCING WILL MAINTAIN TN BORDER PRECIPITATION
OVERNIGHT. BY LATE TONIGHT...MOST OF THE PRECIP NEAR THE TN BORDER
SHOULD FALL A SNOW OR A MIXTURE OF RAIN AND SNOW. THE SNOW THAT DOES
FALL WILL LIKELY HAVE HIGH MOISTURE CONTENT...ALLOWING IT TO
ACCUMULATE TO TREES AND POWERLINES. THERE IS SOME UNCERTAIN WITH
SOIL TEMPERATURES...SOME READINGS REMAIN VERY WARM ACROSS THE
REGION. THE WARM SOIL WILL LIKELY REDUCE ANY ACCUMS INITIAL...BUT
UNTREATED BRIDGES AND OVERPASSES WILL SEE THE FIRST SFC ACCUMS.
THEREFORE...ANY ACCUMS ON THE GROUND TONIGHT WILL LIKELY REMAIN LESS
THAN AN INCH. THE MAIN ISSUE WILL BE WINTER PRECIPITATION
ACCUMULATING ON TREES AND POWERLINES...COUPLED WITH STRONG NW WIND
GUSTS. GIVEN THIS SCENARIO...WE WILL UPGRADE THE HIGH WIND WATCH
ACROSS THE NRN MTNS AND FOOTHILLS TO A WARNING. ELSEWHERE ACROSS THE
MTNS...WE WILL HIGHLIGHT THE WINDS WITH A HIGH WIND WATCH. IT
APPEARS THAT SIGNIFICANT PUBLIC IMPACT...RELATED TO POWER OUTAGES
AND DOWN TREES AND LIMBS WILL DEVELOP LATE TONIGHT...ESPECIALLY
NEAR THE TN BORDER OF THE NRN MTNS.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 415 AM SUNDAY...THE LATEST GFS AND NAM ARE IN GOOD AGREEMENT
IN BRINGING SANDY ONTO THE JERSEY COAST MONDAY NIGHT...THEN DRIVING
THE STORM INTO NORTHERN MARYLAND BY TUESDAY EVENING. THE LOW WILL
THEN SLOWLY LIFT TO THE NORTHEAST AS THE STRONG REX BLOCK OVER THE
NORTH ATLANTIC BREAKS DOWN BY TUE NIGHT.

THERE WILL A STRONG PRESSURE GRADIENT ON THE SOUTHWEST SIDE OF THE
SYSTEM. I CAN/T SAY I/VE EVEN SEEN A 960 MB LOW APPROACHING US FROM
THE NE ALONG WITH STRONG COLD ADVECTION. ONCE MIXING STARTS ON
MONDAY...I/D EXPECT WINDS TO REACH HIGH WIND WARNING CRITERIA OVER
MOST OF THE MTNS AND NC FOOTHILLS. IN FACT...THEY COULD EXTEND
ACROSS OTHER PARTS OF THE FOOTHILLS AND EVEN THE PIEDMONT BOTH
MONDAY AND AGAIN TUESDAY AFTERNOON. FOR NOW I/VE ISSUED A HIGH WIND
WATCH FOR ALL THE MTNS OF THE CAROLINAS AND NE GA AND THE NC
FOOTHILLS THAT ARE NOT ALREADY IN A HIGH WIND WARNING. ABUNDANT HIGH
CLOUDS COULD LIMIT THE MIXING AWAY FROM THE MTNS...WHICH IS WHY I
HAVE NOT EXTENDED THE WATCH ANY FURTHER EAST. THE HIGH WIND WATCH
WILL RUN THROUGH THE END OF THE DAY TUESDAY. BUT PARTS OF THE
MOUNTAINS AND FOOTHILLS COULD SEE DAMAGING WINDS EVEN INTO TUESDAY
NIGHT.

SNOW AMOUNTS HAVE BEEN RAMPED UP...AND A WINTER STORM WATCH WILL BE
ISSUED FOR ALL OF THE NC MTNS WITH THE EXCEPTION OF THE SRN TIER
RUNNING FROM MACON COUNTY TO HENDERSON COUNTY. THESE AREAS WILL SEE
DOWNSLOPE DRYING AND WARMING...AND WHILE THERE WILL BE A FEW PERIODS
OF SYNOPTICALLY DRIVEN FORCING THAT WILL DRIVE SNOW SHOWERS INTO
THESE ZONES...I DON/T SEE THEM EVEN APPROACHING WINTER STORM
CRITERIA. OVER THE NORTHERN MOUNTAINS AND THE HIGHER ELEVATIONS NEAR
THE TN LINE IT/S A WHOLE DIFFERENT STORY. SOME OF THE MODEL SNOWFALL
TOTALS ARE VERY IMPRESSIVE IN THIS AREA. THE WATCH COULD HAVE BEEN
FOR ELEVATIONS ABOVE 3500 FEET OVER THE SOUTHWEST AND CENTRAL
MOUNTAINS. FOR EXAMPLE...I DOUBT BRYSON CITY OR ROBBINSVILLE WILL
SEE MUCH SNOW. BUT AS IT/S A WATCH...AND IT/S VERY EARLY IN OUR
SEASON...I WANTED TO KEEP THE EXTENT RATHER BROAD. THE BEST FORCING
DEVELOPS MONDAY NIGHT AND TUESDAY WHICH IS WHEN THE HEAVIEST SNOW
SHOULD FALL. BUT DURING THE DAY ON MONDAY HIGHER ELEVATIONS WILL
START TO MEASURE...AND SLICK AREAS ARE A GOOD BET WHILE SCHOOL IS IN
SESSION. THEREFORE WE HAVE STARTED THE WATCH AT 10 UTC ON MONDAY.

I WENT BELOW THE GUIDANCE FOR MTN TEMPS MONDAY AND TUESDAY...
BLENDING IN THE SREF 2 METER TEMPS. POPS AND QPF WERE DERIVED FROM
THE SREF AS WELL AS HPC/S QPF. WE WILL HAVE A STORM TOTAL SNOWFALL
GRID AVAILABLE SHORTLY.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 415 AM SUNDAY...NO TIME TO UPDATE THE EXTENDED ON THIS SHIFT.
I/M TRY TO GET TO IT BEFORE LEAVING. HERE IS THE EXTENDED DISCUSSION
FROM YESTERDAY AFTERNOON...

PREVIOUS DISCUSSION...AS OF 2 PM SATURDAY...THE LATEST GUIDANCE OUT
IN THE MEDIUM RANGE HOLDS ONTO THE IDEA THAT ANOTHER SURGE IN NW
FLOW PRECIP PRODUCTION WILL OCCUR ON TUESDAY NIGHT. THIS IS SEEN IN
BOTH THE GFS AND THE 00Z ECMWF. WHAT IS INTERESTING IS THAT THE GFS
HAS UPPER SUPPORT WITH A STRONG VORT LOBE MOVING ACROSS THE MTNS
WITH GOOD DPVA AND MOISTURE UP ABOVE 700 MB...SUGGESTING IT WILL BE
MOIST UP TO A HIGH ENOUGH ALTITUDE FOR ICE NUCLEI TO REMAIN ACTIVE.
WITH THAT IN MIND... THE CHANCE POP WILL BE EXTENDED THROUGH TUE
NIGHT AND INTO WEDNESDAY MAINLY FOR SNOW SHOWERS ON THE TN BORDER. A
FEW MORE INCHES COULD ACCUMULATE IF THE GFS PRECIP AMTS ARE TO BE
BELIEVED. TEMPS WILL REMAIN WELL BELOW NORMAL.

THE MOISTURE WILL FINALLY START TO PULL OUT ON WEDNESDAY NIGHT AS
THE REMNANT LOW MOVES AWAY. WE WILL REMAIN UNDER A DEEP NW FLOW
ALOFT AS AN EXPANSIVE AREA OF SURFACE HIGH PRESSURE STARTS TO BUILD
IN FOR THE LATTER HALF OF THE WEEK. THIS WILL KEEP TEMPS BELOW
NORMAL THROUGH AT LEAST FRIDAY. SOME MODERATION SHOULD HAPPEN ON
SATURDAY AS HEIGHTS RISE AND HIGH PRESSURE MOVES IN.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
AT KCLT...AT 6Z...THE TERMINAL WAS ON THE WESTERN EDGE OF THE REGION
OF GUSTY WINDS ASSOCIATED WITH SANDY. IT APPEARS THAT PERIODS OF
GUSTY CONDITIONS MAY REMAIN UNTIL 10Z...THEN 35010KT SHOULD HOLD
UNTIL MID MORNING. SKY COVER SHOULD REMAIN DOMINATED BY THICK CIRRUS
THROUGH SUNRISE. BY 15Z...DEEPENING MIXING SHOULD SUPPORT THE
REDEVELOPMENT OF GUSTS AROUND 17 KTS. NAM FORECAST SOUNDINGS
INDICATES THAT A LAYER OF MVFR CLOUDS MAY DEVELOP AROUND MID DAY...I
WILL HIGHLIGHT WITH A TEMPO BETWEEN 15Z - 19Z. GUSTS WILL STRAIGHTEN
DURING THE LATE AFTERNOON AND REMAIN THROUGH THE END OF THE TAF
PERIOD. FORECAST SOUNDINGS INDICATE A THICK LAYER OF CLOUDS WILL
DEVELOP WITH THE ARRIVAL OF GREATER SYNOPTIC SCALE FORCING LATE THIS
AFTERNOON AND EVENING...I WILL FORECAST OVC060.

KAVL...OBS TRENDS AND FORECAST SOUNDINGS INDICATE THAT LMVFR TO IFR
CEILINGS FROM UPSLOPE CLOUDS WILL DOMINATE THE TERMINAL SKY THROUGH
THE TAF PERIOD. SHRA MAY DEVELOP NEAR THE TERMINAL THIS AFTERNOON
WITH THE ARRIVAL OF SYNOPTIC SCALE FORCING AND STRENGTHEN NW
FLOW. AT THIS TIME...I WILL KEEP THE TAF DRY DUE TO PLACEMENT AND
TIMING UNCERTAINTY...PRECIP POTENTIAL WILL INCREASE SIGNIFICANTLY
CLOSER TO THE TN LINE. NORTH WINDS WILL REMAIN GUSTY THROUGH THE TAF
PERIOD. GUSTS WILL REMAIN IN THE L20S KTS THIS MORNING AND WILL
INCREASE TO 30 KTS BY EARLY THIS EVENING.

ELSEWHERE...NORTH-NORTHWEST WINDS BETWEEN 6-10KTS AND BKN TO OVC
CIRRUS WILL REMAIN OVER THE FOOTHILL AND PIEDMONT TERMINALS THROUGH
EARLY THIS MORNING. BY 15Z...DEEPENING MIXING SHOULD SUPPORT THE
REDEVELOPMENT OF GUSTS AROUND 17 KTS. GUSTS WILL STRENGTHEN DURING
THE AFTERNOON AND REMAIN THROUGH THE END OF THE TAF PERIOD.
FORECAST SOUNDINGS INDICATE A THICK LAYER OF CLOUDS WILL DEVELOP
WITH THE ARRIVAL OF GREATER SYNOPTIC SCALE FORCING THIS AFTERNOON
AND EVENING...I WILL FORECAST BKN TO OVC BETWEEN 040 TO 060 KFT.

OUTLOOK...THE CIRCULATION AROUND TROPICAL CYCLONE SANDY WILL YIELD
GUSTY NORTH TO NORTHWEST WINDS ACROSS THE WESTERN CAROLINAS MONDAY
AND TUESDAY. UPSLOPE CLOUDS ACROSS THE NORTH CAROLINA
MOUNTAINS WILL CREATE RESTRICTIVE CEILINGS...ESPECIALLY DURING THE
EARLY MORNING HOURS.

AN EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLE SHOWING THE
PERCENTAGE OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED ISSUANCE
CATEGORY IS AVAILABLE AT FOLLOWING LINK (USE LOWER CASE)...

WWW.WEATHER.GOV/GSP/AVIATION/TABLES.HTM

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...HIGH WIND WATCH FROM LATE TONIGHT THROUGH TUESDAY EVENING FOR
     GAZ010-017.
     FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT MONDAY FOR
     GAZ010.
NC...HIGH WIND WATCH FROM LATE TONIGHT THROUGH TUESDAY EVENING FOR
     NCZ035-048-051>053-056-058-059-062>065-502-504-506>510.
     FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT MONDAY FOR
     NCZ033-048>053-058-059-062>065-501-503-505-507-509.
     WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY EVENING
     FOR NCZ048-051>053-058-059.
     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO 8 PM EDT TUESDAY
     FOR NCZ033-049-050-501-503-505.
     WINTER STORM WATCH FROM MONDAY MORNING THROUGH LATE TUESDAY
     NIGHT FOR NCZ033-049-050-501-503-505.
SC...HIGH WIND WATCH FROM LATE TONIGHT THROUGH TUESDAY EVENING FOR
     SCZ001>003.

&&

SYNOPSIS...MCAVOY
NEAR TERM...NED
SHORT TERM...MCAVOY
LONG TERM...MCAVOY
AVIATION...NED

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