Winter Weather in North Carolina, February 19, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1032 PM EST SAT FEB 18 2012

.SYNOPSIS...
LOW PRESSURE WILL MOVE FROM THE NORTHERN GULF COAST TONIGHT TO THE
CAROLINA COAST ON SUNDAY.  THIS WILL BRING WET WEATHER UNTIL THE
SYSTEM MOVES OUT OVER THE ATLANTIC.  HIGH PRESSURE WILL BUILD INTO
THE REGION MONDAY AND REMAIN THROUGH TUESDAY. A SERIES OF COLD
FRONTS WILL MOVE ACROSS THE REGION DURING THE LAST HALF OF THE WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 955 PM...LIGHT RAIN CONTINUES TO MAKE SLOW PROGRESS EAST/
NORTHEAST...AND CURRENTLY EXTENDS FROM THE NORTHEAST GEORGIA
MOUNTAINS TO THE EASTERN SC PIEDMONT. JUDGING FROM UPSTREAM RADAR
TRENDS...THE NAM SEEMS TO BE VERIFYING VERY WELL IN TERMS OF KEEPING
OUR NORTHERN ZONE DRY THROUGH MOST OF THE NIGHT. POPS WERE LOWERED
TO LIKELY IN THESE AREAS...BUT EVEN THIS MAY BE TOO HIGH. THE
CURRENT PRECIP...FORCED BY LOW-TO-MID LEVEL FRONTOGENESIS IS
EXPECTED TO SHIFT EAST OF THE AREA...SOMETIME BETWEEN 09Z AND 12Z.
THERE WILL BE A BIT OF A LULL BEFORE THE MORE SIGNIFICANT
DEFORMATION ZONE PRECIP ARRIVES DURING MID-TO-LATE MORNING.

OTHERWISE...THE COLD AIR ASSOCIATED WITH CANADIAN HIGH PRESSURE
ACROSS THE MIDWEST IS BEGINNING TO SPILL INTO NORTHERN VIRGINIA AT
THIS TIME. BACKDOOR FRONT SHOULD ARRIVE TO THE NORTHERN ZONES BY
12Z...BRINGING MUCH COOLER AIR TO THE REGION.

SUNDAY...THERE ISNT A WHOLE LOT TO ADD FOR SUNDAY AT THIS TIME. THE
MODELS GENERALLY AGREE THAT THE HIGHEST DEFORMATION ZONE QPF WILL
OCCUR ACROSS WESTERN AND NORTHERN PORTIONS OF THE CWFA. BY EARLY
AFTERNOON...MOST AREAS OF THE NORTHERN MOUNTAINS SHOULD BE NEAR
FREEZING. MODEL SOUNDINGS DEPICT A BIT OF A WARM NOSE LINGERING IN
WANING LOW/MID LEVEL WARM ADVECTION. THEREFORE...THERE PROBABLY WILL
BE A TRANSITORY PERIOD OF FZRA/SLEET BEFORE THE TRANSITION TO SNOW.
THIS WILL ALSO BE POSSIBLE FURTHER SOUTH ALONG THE EASTERN
ESCARPMENT AS TEMPS FALL THEN LOCK IN AROUND FREEZING IN THE STRONG
EASTERLY FLOW. SNOW SHOULD BE THE PREDOMINANT PRECIP TYPE IN THE
CURRENT WARNING AREA...AND IT APPEARS THAT 4-6 INCHES ARE EASILY
ATTAINABLE IN THIS AREA. FURTHER SOUTH...LIGHT ACCUMULATIONS OF A
MIXED BAG ARE EXPECTED ALONG THE EASTERN ESCARPMENT. MEANWHILE...
THE INTERIOR VALLEYS (INCLUDING ASHEVILLE/HENDERSONVILLE/
WAYNESVILLE) WILL LIKELY SEE AROUND AN INCH OR LESS AS PRECIP
CHANGES TO SNOW BEFORE ENDING.

ANOTHER AREA OF CONCERN WILL BE THE I-40 CORRIDOR IN THE
PIEDMONT...AS SUFFICIENT COLD AIR SHOULD BE IN PLACE TO ALLOW FOR
ACCUMULATING SNOWFALL BY THE TIME PRECIP ENDS LATE TOMORROW
AFTERNOON/EVENING. PER COORDINATION WITH NEIGHBORING OFFICES...AN
ADVISORY WILL NOT BE ISSUED FOR THESE AREAS ATTM...BUT MEASURABLE
SNOWFALL DOES APPEAR LIKELY BEFORE PRECIP ENDS.

THE FINAL AREA TO WATCH WILL BE THE HIGHER ELEVATIONS OF THE CENTRAL
NC MTNS...ESPECIALLY ALONG THE TENN BORDER. THE CONCERN HERE IS THAT
AS THE HEAVIER DEFORMATION ZONE PRECIP MOVES OVER THIS AREA...SNOW
LEVELS WILL QUICKLY PLUMMET AND A GOOD CHUNK OF TOMORROWS PRECIP
COULD END UP FALLING AS SNOW ABOVE 3000 FEET OR SO. THIS IS ENOUGH
OF A CONCERN THAT A WINTER STORM WATCH WILL BE ISSUED FOR THE HIGHER
ELEVATIONS OF HAYWOOD AND MADISON COUNTIES.

.PREVIOUS SUNDAY DISCUSSION...
SUNDAY...THE LOW PRESSURE CENTER IS PROGGED TO TRACK QUICKLY FROM
NRN GA TO THE SE NC COASTAL WATERS BY 00Z MONDAY AND DEEPEN TO
AROUND 1000 MB. IN THE UPPER LEVELS THE STRONGEST Q CONVERGENCE WILL
CROSS THE CWFA SUNDAY MORNING. THEN A DEFORMATION ZONE WILL BEGIN TO
PIVOT AND SHIFT EAST FROM ERN KY/TN TO THE NC MTNS BY EVENING. BOTH
THE NAM AND GFS FCST SNDGS SHOW PROFILES IN THE NRN MTNS CHANGING
FROM RA TO SN FROM LATE MORNING THRU THE AFTN HOURS. THE NAM TRIES
TO HOLD ONTO A WARM NOSE...BUT THIS SCENARIO SEEMS UNLIKELY WITHIN A
DEFORMATION ZONE. USING A TOP-DOWN APPROACH FAVORING THE GFS
PROFILES...RAIN CHANGES TO SNOW ACRS THE NRN NC MTNS AND ADJACENT
BLUE RIDGE STARTING AROUND 15Z...WITH SNOW LEVELS DROPPING THRU THE
DAY. MEANWHILE...A DRY SLOT WILL PUNCH INTO THE SRN HALF OF THE
CWFA...SO POPS SHUD TAPER OFF. (ALTHOUGH DRIZZLE MAY LINGER THRU THE
DAY.) AS FOR ACCUM...TAKING A BLEND OF GUIDANCE AND USING HPC/S
SLR...THE CURRENT WATCH ZONES DO REACH 12-HR WARNING CRITERIA.
OUTSIDE OF THOSE AREAS...IT IS HIGHLY ELEVATION-DEPENDENT...WITH THE
SW NC MTNS GETTING ONLY ADVISORY-LEVEL SNOW ABOVE ABOUT 5000 FT.
ALSO...THE I-40 CORRIDOR MAY GET SOME SNOW ACCUM AS THE LOW EXITS
LATE SUN AFTN/EVE. CONFIDENCE SEEMS HIGH ENUF TO UPGRADE THE WATCH
TO A WINTER STORM WARNING...BUT NO HIGH ENUF TO ISSUE ANYTHING
OUTSIDE THAT AREA. WILL MENTION POTENTIAL IMPACTS FOR THE REST OF
THE MTNS IN THE HWO.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 230 PM SATURDAY...A GFS/ECMWF BLEND WAS USED FOR THIS FCST
PERIOD WITH THE NAM CONSIDERED AN OUTLIER. AS UPPER TROF PULLS OFF
TO THE NE AND SFC LOW TRACKS OFF THE CAROLINA COAST PRECIP CHC DROPS
OFF SUN NIGHT AND LATEST GFS BUFKIT SOUNDINGS ELIMINATES WARM NOSE
ALOFT...WHICH KEEPS TEMP PROFILES COLD ENOUGH FOR RAIN/SNOW PIEDMONT
AND SNOW MTNS BEFORE IT ENDS AFTER MIDNIGHT. MON MRNG LOWS WILL BE
IN THE U20S-L30S ACROSS THE PIEDMONT WITH 20S MTNS. UPPER RIDGE AND
SFC HIGH PRES BUILD OVER THE REGION MON WITH LOWS ABOUT 5 DEG BELOW
AVG. RIDGE MOVES E MON NIGHT-TUE AND AS SFC HI MOVES OFFSHORE...S
RETURN FLOW BEGINS TO PICK UP. TEMPS WARM TO NEAR AVG AND MOISTURE
STARTS TO ADVANCE NE TOWARD THE AREA AS THE NEXT SHORTWAVE
APPROACHES FROM THE W. FOR NOW INCREASED CLOUDS OVER THE AREA BUT
HELD POPS BELOW SLIGHT CHC THRESHOLD THRU THE DAY TUE.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM SATURDAY...A STRONG POSITIVE HEIGHT ANOMALY WILL BE
LOCATED OFF THE US WEST COAST AT THE START OF THE EXTENDED RANGE
FORECAST. THIS WILL KEEP THE ERN CONUS UNDER A BROAD TROUGH THROUGH
MOST OF THE WED-SAT PERIOD. WHILE THE GFS AND ECMWF ARE IN GENERAL
AGREEMENT WITH THE SIGNIFICANT SYNOPTIC SCALE FEATURES...THERE
CONTINUE TO BE SHORT WAVE...AND THUS SENSIBLE WX DIFFERENCES...IN
THEIR SOLUTIONS. HPC HAS ACCOUNTED FOR THIS BY GOING MAINLY WITH A
BLEND OF THE GFS AND ECMWF ENSEMBLES FROM WED ONWARD.

FOR TUE NIGHT/WEDNESDAY...A POTENT SHORT WAVE WILL LIFT ACROSS THE
NEW ENGLAND STATES TUE NIGHT. STRONG RIDGING DOWN ACROSS THE GULF
WILL LIMIT THE SFC REFLECTION OF THE TROUGH THIS FAR SOUTH. IN
FACT...THERE ISN/T AN IDENTIFIABLE SFC FRONT...OR MUCH FORCING...AND
THAT PART OF THE FORECAST WILL REMAIN DRY. THE LLVL THICKNESSES
IMPLY WELL ABOVE NORMAL TEMPERATURES ON WED AS WELL.

THE LONG WAVE THROUGH WILL DEEPEN A LITTLE OVER THE ERN STATES WED
NGHT/THU...AIDED BY A SHORT WAVE THAT CROSSES THE FA THU MORNING.
CHANCE POPS HAVE BEEN ADDED TO THE FORECAST AHEAD OF THIS THROUGH.
TEMPERATURES STILL LOOK MILD...AND ONLY RAIN IS EXPECTED. THE
ENSEMBLES HAVE ANOTHER SHORT WAVE CROSSING THE FA ON FRIDAY. TIMING
THIS SERIES OF SHORT WAVES FOR THE THU/FRI TIME FRAME IS NEARLY
IMPOSSIBLE...AND LOW CHANCE POPS HAVE BEEN SPREAD OUT ACROSS MOST OF
BOTH DAYS. IN REALITY...PCPN CHANCES WILL PROBABLY BE CONFINED TO
SHORTER INTERVALS...BUT THOSE INTERVALS CANNOT BE NAILED DOWN.

INTERESTINGLY...THERE IS PRETTY GOOD AGREEMENT ON THE LONG WAVE AXIS
PUSHING EAST OF THE REGION ON DAY 7 AND INTO NEXT SUNDAY...AND THAT
PART OF THE FORECAST LOOKS PRETTY GOOD. HOWEVER...MUCH COLDER AIR
WILL PROBABLY FOLLOW THE THOUGH...WITH THE PERIOD OF ABOVE NORMAL
TEMPS COMING /BRIEFLY?/ TO AN END AT THE END OF THE EXTEND RANGE.

&&

.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
AT KCLT/KHKY...LIGHT RAIN WILL GRADUALLY SPREAD NORTH ACROSS THE
WESTERN CAROLINAS THIS EVENING...REACHING KCLT AND KHKY BETWEEN 05Z
AND 07Z. VFR CONDITIONS WILL ACCOMPANY THE PRECIP FOR THE FIRST
COUPLE OF HOURS...BUT AS THE LOWER LEVELS SATURATE...MVFR CONDITIONS
ARE EXPECTED BY DAYBREAK...WITH IFR CIGS EXPECTED BY AROUND SUNRISE.
RAIN/IFR CONDITIONS WILL PERSIST THROUGH MOST OF SUNDAY. LIGHT SOUTH
WINDS WILL BECOME NE AFTER MIDNIGHT...AS COLD HIGH PRESSURE OVER THE
MIDWEST BEGINS TO SPILL EAST OF THE APPALACHIANS. NE WINDS ARE
EXPECTED TO BECOME FAIRLY STRONG BY LATE MORNING...GENERALLY AROUND
15 KT WITH SOME GUSTS IN THE LOWER 20S POSSIBLE. BY THE END OF THE
PERIOD...ENOUGH COLD AIR WILL SPILL INTO THE REGION TO ALLOW RAIN TO
MIX WITH SLEET AND SNOW AT KHKY BEFORE ENDING. THE PROBABILITY OF
THIS OCCURRING AT KCLT IS LOW...BUT NOT ZERO.

ELSEWHERE...RAIN WILL OVERSPREAD THE UPSTATE SC TERMINALS AND KAVL
THIS EVENING. ALTHOUGH VFR CONDITIONS WILL LINGER FOR A COUPLE OF
HOURS AFTER PRECIP BEGINS...MVFR IS EXPECTED AT ALL TERMINALS BY
06Z. IFR SHOULD THEN SETTLE IN AFTER MIDNIGHT...AND LINGER THROUGH
THE DAY SUNDAY. COLD HIGH PRESSURE OVER THE MIDWEST WILL BEGIN TO
SPILL EAST OF THE APPALACHIANS TONIGHT...WHICH WILL ALLOW WINDS TO
TURN TO THE NE BY DAYBREAK. WINDS ARE EXPECTED TO BECOME FAIRLY
STRONG BY LATE MORNING...GENERALLY AROUND 15 KT WITH SOME GUSTS IN
THE LOWER 20S POSSIBLE. BY THE END OF THE PERIOD...ENOUGH COLD AIR
WILL SPILL INTO THE REGION TO ALLOW RAIN TO MIX WITH SLEET AND SNOW
AT KAVL BEFORE ENDING.

OUTLOOK...PRECIP WILL CHANGE TO ALL SNOW AT KAVL BY SUNDAY
EVENING...WITH LIGHT ACCUMULATIONS POSSIBLE. OTHERWISE...PRECIP WILL
BECOME TO AN END...AND GRADUALLY IMPROVING FLT CONDITIONS ARE
EXPECTED SUNDAY NIGHT INTO EARLY MONDAY. QUIET WX CONDS ARE
EXPECTED  MONDAY AND TUESDAY WITH SHOWER CHANCES INCREASING
WEDNESDAY.

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...NONE.
NC...WINTER STORM WARNING FROM 7 AM SUNDAY TO MIDNIGHT EST SUNDAY
     NIGHT FOR NCZ033-049-050-501-503-505.
     WINTER STORM WATCH FROM 7 AM EST SUNDAY THROUGH SUNDAY EVENING
     FOR NCZ048-052.
SC...NONE.

&&

SYNOPSIS...DEO
NEAR TERM...ARK/JDL
SHORT TERM...RB
LONG TERM...MCAVOY
AVIATION...JDL

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