Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 120307
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1007 PM EST THU FEB 11 2016

.SYNOPSIS...
A FAST-MOVING UPPER LEVEL DISTURBANCE WILL BRING A BRIEF CHANCE OF
PRECIPITATION TO PARTS OF THE AREA FRIDAY. A STRONGER DOME OF
CANADIAN HIGH PRESSURE WILL SETTLE IN FOR THE WEEKEND...USHERING IN
ANOTHER PERIOD OF COLD TEMPERATURES. THIS WILL BE FOLLOWED BY
ANOTHER WEATHER SYSTEM WHICH WILL PRODUCE A BETTER CHANCE OF
PRECIPITATION EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
AT 10 PM...CLOUD COVER ASSOCIATED WITH A CLIPPER WAS STREAMING
ACROSS THE MID MISSISSIPPI RIVER VALLEY. REGIONAL RADAR INDICATED A
LARGE FIELD OF LIGHT REFLECTIVITY ACROSS KY AND W. TN. THE LATEST
OBSERVED POSITION OF THE CLOUD COVER AND RADAR RETURNS AGREE WELL
WITH THE LATEST RUNS OF GUIDANCE. I WILL UPDATE THE FORECAST TO
ALIGN WITH RECENT OBSERVATIONS OF TEMP/DWPTS. OTHERWISE...THE
CURRENT FORECAST APPEARS ON TRACK.

AT 710 PM...LIGHT NORTHWEST WINDS AND THIN HIGH CLOUDS WILL REMAIN
ACROSS THE WESTERN CAROLINAS AND NE GA THROUGH THIS EVENING. LATEST
GUIDANCE INDICATES THAT AN ALBERTA CLIPPER WILL RACE ACROSS THE
WESTERN CAROLINAS FRIDAY MORNING. THE COMBINATION OF DEEP MOISTURE
AND FORCING WILL SUPPORT LIGHT SNOW SHOWERS TO FLURRIES ACROSS THE
REGION FROM EARLY FRIDAY MORNING INTO THE EARLY AFTERNOON. I WILL
UPDATE THE FORECAST WITH THE LATEST THINKING.

AT 230 PM THURSDAY...AN UPPER TROUGH WILL REMAIN OVER THE EASTER USA
TONIGHT AND FRIDAY. CHANNELED UPPER LEVEL VORTICITY ROUNDING THIS
TROUGH WILL APPROACH THE SOUTHERN APPALACHIANS LATE TONIGHT...
CROSSING THE WESTERN CAROLINAS ON FRIDAY. MEANWHILE...AT THE
SURFACE...THE MODELS ARE COMING INTO ALIGNMENT ON DEVELOPING A
SURFACE WAVE OVER THE GULF STATES AHEAD OF AND TO THE SOUTH OF THE
CHANNELED VORTICITY. MODEST ISENTROPIC UPGLIDE TO THE NE OF THIS
SURFACE WAVE WILL SUPPORT PRECIPITATION OVER OUR AREA...STARTING
BEFORE DAYBREAK. VERTICAL PROFILES SUPPORT MAINLY SNOW...WITH
PERHAPS SOME MIXED PRECIPITATION IN THE UPPER SAVANNAH RIVER
VALLEY...THOUGH VERY LITTLE ICE ACCUMULATION IS EXPECTED THERE.

BY MIDDAY THE SURFACE LOW MOVES OFF THE SC COAST WHERE IT CLOSES OFF
AND DEEPENS....WHILE THE BULK OR PRECIPITATION MOVES EAST OF OUR
AREA. VEERING LOW LEVEL WINDS SUPPORT UPSLOPE FLOW SNOW IN THE NC
MOUNTAINS BORDERING TN...WITH RAIN OR FREEZING RAIN IN THE VALLEYS
NEARER THE BLUE RIDGE. AT THIS POINT THE BEST BET FOR SNOW
ACCUMULATIONS APPEARS TO BE IN THE NC MOUNTAINS...WHERE SNOW TOTALS
MAY REACH TWO INCHES ON THE HIGHEST PEAKS NEAR THE TN BORDER.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 245 PM THURSDAY...A RIDICULOUSLY COLD WEEKEND IS IN STORE FOR
THE AREA FOR THE SHORT TERM WITH A STRONG UPPER TROUGH IN PLACE
OVER THE EASTERN SEABOARD AND COLD ARCTIC HIGH PRESSURE BUILDING
IN AT THE SURFACE IN THE WAKE OF THE COLD FRONT CROSSING THE AREA
FRIDAY AND FRIDAY NIGHT. TO START WITH HOWEVER...WE WILL CONTINUE
TO SEE SOME LINGERING NORTHWEST FLOW SNOW SHOWERS IN THE NORTHERN
MOUNTAINS THROUGH EARLY SATURDAY...THOUGH DO NOT REALLY EXPECT
MUCH MORE IN THE WAY OF ADDITIONAL ACCUMULATION...MAYBE ANOTHER
HALF INCH AT MOST BUT PROBABLY NOT EVEN THAT AS MOISTURE IS PRETTY
ANEMIC THROUGH THE COLUMN. OTHER CONCERN WILL BE TIGHT PRESSURE
GRADIENT AS THE SURFACE HIGH BUILDS IN...WHICH WILL LEAD TO STRONG
WINDS OVER THE MOUNTAINS. DO NOT QUITE MEET WIND ADVISORY CRITERIA
EXCEPT AT THE HIGHEST ELEVATIONS...BUT WITH COLDER TEMPERATURES
FILTERING IN...DEFINITELY HAVE WIDESPREAD WIND CHILL ADVISORY
CRITERIA OVER THE MOUNTAINS. SINCE FRIDAY NIGHT IS STILL 3RD
PERIOD...WILL OPT FOR NOW TO LEAVE THE WIND CHILL WORDING IN THE
HWO BUT AN ADVISORY WILL LIKELY BE NEEDED BY TOMORROW AFTERNOON.

DEEP LAYER...VERY STRONG CAA BUILDS ACROSS THE SOUTHEAST FRIDAY
NIGHT INTO SATURDAY...WITH AT LEAST WEAK CAA CONTINUING THROUGH
SUNDAY MORNING. RESULTING HIGH TEMPERATURES ON SATURDAY WILL BARELY
MAKE IT INTO THE LOWER 40S FOR EXTREME SOUTHERN ZONES...AND REMAIN
IN THE TEENS OVER THE NORTHERN MOUNTAINS. SUNDAY WILL BE EVEN
COLDER AS THE ARCTIC HIGH PRESSURE SETTLES OVERHEAD...WITH HIGHS
AT BEST UPPER 30S EXTREME SOUTH AND AT OR BELOW FREEZING FOR A GOOD
PORTION OF THE AREA. SUNDAY MORNING WILL SEE VERY COLD TEMPERATURES
AS WELL...AND ALL THIS COMBINED WILL LEAD TO AVERAGE TEMPERATURES
THAT MEET COLD WAVE CRITERIA /AVERAGE DAILY TEMPERATURE OF 25 OR
LESS FOR ASHEVILLE...29 OR LESS FOR CHARLOTTE...AND 30 OR LESS FOR
GSP/. WILL CONTINUE TO HIGHLIGHT THIS IN THE HWO BUT MAY HAVE TO
ISSUE AN SPS SOMETIME IN THE NEXT 24-36 HOURS TO COVER THE IMPACTS
FROM THIS.

CLOUDS WILL BE ON THE INCREASE SUNDAY AS THE NEXT SYSTEM
BEGINS DIVING DOWN INTO THE PLAINS...WHICH WILL BE OUR NEXT BIG
WEATHER-MAKER AS WE TRANSITION INTO THE EXTENDED.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 300 PM THURSDAY...THE OPERATIONAL MODELS HAVE COME INTO BETTER
AGREEMENT WITH THE NEXT WEATHER SYSTEM EXPECTED TO AFFECT THE
WESTERN CAROLINAS AND NORTHEAST GA EARLY NEXT WEEK. THE GFS/ECMWF/
CANADIAN ALL HAVE A SIMILAR DEPICTION OF THE AMPLITUDE AND TIMING OF
THE 500 MB TROF EXPECTED TO DIG DOWN OVER THE PLAINS ON SUNDAY
NIGHT...WITH THE TROF AXIS CROSSING THE MS RIVER ON MONDAY
AFTERNOON. THUS...CONFIDENCE IS SLOWLY INCREASING AS THE MODELS
START TO AGREE ON AN OVERALL SCENARIO OF A HIGHER AMPLITUDE TROF...
EVEN IF TIMING REMAINS OFF. THE MODELS GENERALLY SHOW A MORE INLAND
TRACK OF A PRIMARY SURFACE LOW ACROSS N GA MONDAY NIGHT AND THE
CAROLINA PIEDMONT ON TUESDAY MORNING. IF THAT WORKS OUT...IT WOULD
MOST LIKELY MEAN STRONG WARM ADVECTION ACROSS THE PIEDMONT AND
FOOTHILLS MONDAY AFTERNOON AND NIGHT WHICH WOULD ALMOST ASSUREDLY
FORCE A CHANGEOVER TO RAIN ACROSS MOST OF THE PIEDMONT AND EVEN A
GOOD BIT OF THE MTNS. WHAT REMAINS TO BE SEEN IS HOW MUCH FALLS AS
SOMETHING OTHER THAN RAIN BEFORE THE TRANSITION OCCURS. OF
COURSE...UNCERTAINTY REMAINS HIGH...SO THE READER IS URGED TO MANAGE
HIS/HER EXPECTATIONS ACCORDINGLY.

LIGHT PRECIP SHOULD BREAK OUT ACROSS THE FCST AREA SUNDAY NIGHT AND
MONDAY MORNING AS MOISTURE RETURNS AND ISENTROPIC UPGLIDE GRADUALLY
STRENGTHENS TO THE NORTH OF A DEVELOPING WARM FRONT ACROSS THE DEEP
SOUTH. BECAUSE WE SHOULD BEGIN THE EVENT WITH A COLD AND DRY AIR
MASS IN PLACE...ANYTHING THAT FALLS BEFORE ABOUT MIDDAY MONDAY
SHOULD BE IN THE FORM OF SNOW. HOWEVER...AS THE LOW APPROACHES FROM
THE WEST...WARM ADVECTION WILL INCREASE FROM THE SOUTH. THE MODELS
AGREE THAT A WARM NOSE SHOULD DEVELOP ON MONDAY AFTERNOON THAT WILL
BRING A CHANGEOVER TO SLEET AND THEN PERHAPS A BRIEF PERIOD OF
FREEZING RAIN ACROSS THE AREA ALONG AND S OF THE I-85 CORRIDOR. WE
LACK A STRONG PARENT HIGH TO THE NORTHEAST...WHICH IS A SIGNIFICANT
LIMITING FACTOR ON THE WINTER PRECIP POTENTIAL. THUS...IT IS HARD TO
IMAGINE IT WILL NOT BE A MOSTLY RAIN EVENT ACROSS MOST OF THE REGION
MONDAY NIGHT...PERHAPS WITH SOME HEAVY RAIN THAT MIGHT CAUSE MINOR
FLOODING ISSUES.  THE NC FOOTHILLS...BLUE RIDGE...AND PART OF THE NW
PIEDMONT WILL BE THE EXCEPTION...AS USUAL...BECAUSE COLD AIR WILL BE
TRAPPED THE LONGEST...WELL INTO MONDAY NIGHT. AS IT STANDS RIGHT
NOW...THE TRANSITION TO FREEZING RAIN WILL OCCUR EARLY MONDAY
EVENING AND THEN IT WILL STAY THAT WAY INTO EARLY TUESDAY MORNING.
THIS HAS THE POTENTIAL TO PRODUCE ICE ACCUM OF AROUND ONE QUARTER
INCH IN THE I-40 CORRIDOR AND BLUE RIDGE BEFORE THE CHANGEOVER TO
RAIN AROUND DAYBREAK TUESDAY. FORCING IS THE STRONGEST AND MOISTURE
THE DEEPEST MONDAY NIGHT. HAVE LIMITED THE PRECIP PROB TO THE LIKELY
RANGE FOR NOW...MOSTLY OVER UNCERTAINTY IN THE PRECIP TYPE FCST. AS
THE LOW PULLS AWAY TUESDAY...COLDER AIR WILL MOVE BACK IN FROM THE
WEST...AND PRECIP WILL CHANGE BACK OVER TO SNOW ACROSS THE NC
MOUNTAINS AS THE EVENT WINDS DOWN.

AFTER 00Z WEDNESDAY...WITH THE GENERAL EXCEPTION OF THE
MOUNTAINS...SHOULD SEE PRETTY QUIET SENSIBLE WEATHER CONDITIONS
FOR THE END OF THE FORECAST PERIOD. IN THE WAKE OF THE EARLY WEEK
SYSTEM...MEAN UPPER TROUGHING WILL REMAIN IN PLACE OVER THE EASTERN
PORTION OF THE COUNTRY...WITH ANOTHER CLIPPER SYSTEM DIVING DOWN THE
FLOW AND PUSHING INTO THE SOUTHERN APPALACHIANS TUESDAY NIGHT. THE
12Z ECMWF IS MUCH FASTER WITH THIS...REALLY RIGHT ON THE HEELS OF
THE EARLIER SYSTEM AND EXITING IT OUT OF THE AREA BY WEDNESDAY
MORNING. THE GFS HOLDS ONTO SOME UPSLOPE SNOW IN THE NORTHWEST
FLOW ALOFT THROUGH WEDNESDAY NIGHT. HAVE TAKEN SORT OF A BLEND
BUT LEADED TOWARD THE SLIGHTLY SNOWIER SOLUTION OF THE GFS FOR
THE MOUNTAINS AS NORTHWEST FLOW SNOW IS A REASONABLE EXPECTATION
WITH THE STRONG UPPER TROUGH IN PLACE. IT SHOULD WARM UP ENOUGH
ON WEDNESDAY TO CHANGE OVER TO RAIN...BUT WITH BELOW-FREEZING
TEMPERATURES AGAIN WEDNESDAY NIGHT...ANYTHING ELSE THAT FALLS WOULD
BE SNOW BUT VERY LIGHT AND DRY AT THIS POINT...WITH DRY AIR ALOFT
ABOVE ABOUT 750MB /5KFT/ QUICKLY DEVELOPS AS THE BRIEF DEEPER
MOISTURE ASSOCIATED WITH THE CLIPPER MOVES EAST. HAVE INCLUDED
GENERALLY TRACE ACCUMULATIONS OF SNOW.

BEHIND THIS LAST CLIPPER...UPPER RIDGING WILL BUILD INTO THE
CENTER OF THE COUNTRY. OPERATIONAL MODELS AT ODDS WITH THE
PROGRESSIVE NATURE OF THE LONGWAVE SYSTEM...WITH THE ECMWF QUITE
A BIT STRONGER WITH THE UPPER RIDGE...AND RESULTANT CONFLUENT FLOW
OVER THE GREAT LAKES AND NEW ENGLAND ALLOWS A DRY ONSET CLASSICAL
CAD EVENT TO DEVELOP...WHEREAS THE GFS PUSHES THAT UPPER RIDGE
RIGHT ON THROUGH. EITHER WAY THE END OF THE PERIOD LOOKS DRY...JUST
SOME UNCERTAINTY ON TEMPERATURES SO HAVE TAKEN A BLEND AND SHOW A
GENERAL WARMING TREND AS THICKNESSES INCREASE WITH THE INCREASING
UPPER RIDGING.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...LIGHT NORTHWEST WINDS AND THIN HIGH CLOUDS
WILL REMAIN ACROSS THE WESTERN CAROLINAS THROUGH THIS EVENING.
LATEST GUIDANCE INDICATES THAT AN ALBERTA CLIPPER WILL RACE ACROSS
THE WESTERN CAROLINAS FRIDAY MORNING. THE COMBINATION OF DEEP
MOISTURE AND FORCING WILL SUPPORT LIGHT SNOW SHOWERS TO FLURRIES
ACROSS THE REGION FROM EARLY FRIDAY MORNING INTO THE EARLY
AFTERNOON. I WILL HIGHLIGHT THE GREATEST CHC OF SNOW FLURRIES AT
KCLT WITH A TEMPO FROM 15Z TO 19Z. KAVL MAY SEE -SN LINGER FROM 10Z
TO 20Z. KAND...KGMU...KGSP...AND KHKY WILL SEE A SHORT WINDOW FOR
-SN. IN ADDITION...MVFR CLOUDS WILL LIKELY OCCUR WITH THE -SN...MOST
LIKELY AT KAVL. HIGH PRESSURE SHOULD BEGIN TO BUILD FROM THE WEST
DURING THE AFTERNOON...SUPPORTING SOUTHWEST WINDS DURING THE
AFTERNOON.

OUTLOOK...AN ARCTIC AIR MASS WILL BUILD OVER THE REGION THIS
WEEKEND...WITH UPSLOPE CLOUDS ON THE WEST SIDE OF THE APPALACHIANS.
A SIGNIFICANT WINTER WEATHER SYSTEM IS POSSIBLE EARLY NEXT WEEK.

CONFIDENCE TABLE...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH  83%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     MED   60%     HIGH  98%
KHKY       HIGH 100%     HIGH 100%     HIGH  89%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     MED   70%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...NED
SHORT TERM...TDP
LONG TERM...PM/TDP
AVIATION...NED


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