329 
FXUS62 KGSP 251019
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
519 AM EST SAT DEC 25 2010

.SYNOPSIS...
LOW PRESSURE WILL STRENGTHEN AND TRACK EAST ACROSS THE NORTHERN GULF 
OF MEXICO TODAY. THIS LOW WILL DEEPEN AS IT TURNS NORTHEAST ALONG 
THE CAROLINA COAST EARLY SUNDAY AND CONTINUES TO THE NEW ENGLAND 
COAST EARLY MONDAY. COLD CANADIAN HIGH PRESSURE WILL BUILD FROM THE 
MISSISSIPPI VALLEY INTO THE FIRST HALF OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE PAST FEW MODEL RUNS HAVE VEERED DRAMATICALLY BACK INTO THE HEAVY 
SNOW CAMP FOR THE WESTERN CAROLINAS AND NE GA FOR TODAY AND TONIGHT. 

A NRN STREAM STREAM SHORT WAVE IS DIGGING MORE THAN THE MODELS HAD 
ORIGINALLY PREDICTED. THIS FEATURE CONTINUES TO STRENGTHEN AS 
INDICATED BY THE INCREASING DARK BAND ON WATER VAPOR IMAGERY OVER 
THE SRN PLAINS. THIS IS RESULTING IS DOWNSTREAM UPPER DIVERGENCE AND 
QG FORCING. A BAND OF 600 MB FRONTOGENESIS EXTENDS ACROSS TN AND 
INTO WRN NC. THIS BAND IS MOST CLOSELY ASSOCIATED WITH THE PCPN OVER 
SRN TN. THE FRONTOGENESIS IS PROGGED TO STRENGTHEN THROUGH 18 
UTC...WHICH MATCHES THE INCREASING PCPN TREND. THE LATEST GFS AND 
ECMWF NOW HAVE 0.50 TO 0.75 INCHES OF LIQUID EQUIVALENT PCPN OVER 
THE MTNS OF NC/SC/GA AND THE NC FOOTHILLS THROUGH 00 UTC TODAY. WITH 
A SNOW RATIO OF 12:1...THIS WOULD YIELD OVER 8 INCHES OF SNOW IN 
SPOTS. WE/VE BEEN PLAYING CATCHUP WITH THIS EVENT...AND THE 6 INCH 
TOTALS I HAVE IN THE CENTRAL AND SRN NC MTNS TODAY WILL PROBABLY 
NEED TO BE BUMPED UP ANOTHER COUPLE INCHES AT LEAST. THIS AMOUNT OF 
SNOW IS LIKELY TO DOWN TREES...CAUSE POWER OUTAGES AND WILL MAKE 
CHRISTMAS TRAVEL NEARLY IMPOSSIBLE OVER MUCH OF THE MTNS BY LATER IN 
THE MORNING....WITH THE NC FOOTHILLS EXPERIENCING SIMILAR CONDITIONS 
LATER IN THE DAY. IN SHORT...THIS IS GOING TO BE A SIGNIFICANT AND 
DANGEROUS WINTER STORM FOR THE MTNS AND FOOTHILLS TODAY.

THEN THERE IS PART TWO. A POTENT SRN STREAM SHORT WAVE...WHICH IS 
ONLY INDIRECTLY RESPONSIBLE FOR THE HEAVY SNOW TODAY...WILL BE 
PICKED UP BY THE NRN STREAM WAVE. AS THE NRN STREAM WAVE IS SLOWER 
AND DEEPER...IT LOOKS TO PHASE MORE WITH THE SRN STREAM ENERGY THAN 
ORIGINALLY EXPECTED. AS STRONG DEEP LAYER Q-VECTOR CONVERGENCE 
DEVELOPS OVER THE REGION TONIGHT...A PIVOTING BAND OF SNOW IS 
EXPECTED TO CONTINUE OVER THE EASTERN PART OF THE FA. BOTH NAM AND 
GFS CROSS SECTIONS SHOW A GOOD AREA OF NEGATIVE EPV CROSSING THE 
FOOTHILLS AND PIEDMONT TOWARD 0600 UTC. AS THIS HAPPENS...A PERIOD 
OF HEAVY SNOW IS EXPECTED ACROSS THE I-77 CORRIDOR AND INTO THE 
CENTRAL AND SOUTHERN UPSTATE. FOR NOW I/M JUST GOING WITH 2 TO 4 
INCHES OF SNOW FOR THESE AREAS...WHICH IS STILL ENOUGH TO WARRANT A 
WINTER STORM WARNING UP THE I-85 AND I-77 CORRIDORS. HOWEVER...IF 
THIS WESTWARD ADJUSTMENT AND PHASING CONTINUES...THEN HEAVIER SNOW 
IS VERY POSSIBLE.

THIS IS SOMETHING TO KEEP IN MIND FOR THE URBAN CORRIDOR FROM 
GREENVILLE-SPARTANBURG UP TO THE CHARLOTTE METRO AREAS. IT WILL TAKE 
SOME TIME FOR THE LOWEST LEVELS TO COOL TODAY AND FOR ALL SNOW TO 
FALL ACROSS THESE AREA. HOWEVER...THIS SECONDARY AREA OF FORCING 
WITH THE SRN STREAM WAVE IS LIKELY TO REINVIGORATE THE PCPN THIS 
EVENING...RESULTING IN A RAPID TRANSITION TO HEAVY SNOW WHERE THERE 
WAS A MIX BEFORE. STILL...I THINK THE URBAN CORRIDOR WILL CHANGE 
OVER IN THE 19 TO 20 UTC TIME FRAME...WHICH IS PLENTY OF TIME TO 
WATCH THE SNOW FALL AND EXPERIENCE A WHITE CHRISTMAS OVER THE 
PIEDMONT.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
AS OF 330 AM SATURDAY...BY SUNRISE SUNDAY...A RAPIDLY DEEPENING SFC 
LOW IS EXPECTED TO BE OFF THE CAROLINA COAST AS A MID LEVEL TROF 
AMPLIFIES AND CLOSES OFF OVER THE SOUTHERN APPALACHIANS. CONSIDERING 
ONLY THE QG FORCING...DEEP LIFT WILL REMAIN OVER THE WESTERN 
CAROLINAS 12Z SUNDAY AS MID LEVEL HEIGHTS DECREASE SIGNIFICANTLY 
AHEAD OF THE TROF. THE WESTERN CAROLINAS SHOULD REMAIN WITHIN A 
COMMA HEAD REGION OF DEEP LIFT...MOISTURE...AND COLD AIR THROUGH 0Z 
MONDAY. THE POSITION OF THE MID LEVEL LOW SHOULD SUPPORT ONGOING 
SNOWFALL ACROSS THE CWA DURING THE MORNING. DURING THE 
AFTERNOON...MID LIFT WILL PIVOT NORTH AND H85 FLOW WILL BACK 
NW...BECOMING DOWNSLOPE EAST OF THE MTNS. I WILL TIME CHC TO SCHC 
POPS EAST THROUGH THE DAY. ACROSS THE MTNS...MOIST AND COLD NW FLOW 
WILL COMBINE WITH LINGERING MID LEVEL SUPPORT TO INCREASE SHSN 
ACROSS THE WESTERN NC MTNS THROUGH THE REST OF THE DAY. BASED ON NAM 
QPF AND A CONSERVATIVE 15 TO 1 SLR...I WILL FORECAST 1 TO 2 INCHES 
PER 3 HRS ACROSS THE TN BORDER COUNTIES ON SUNDAY. HIGHS ON SUNDAY 
WILL RANGE FROM THE U20S TO 30 ACROSS THE MTNS TO MID 30S EAST.

SUNDAY NIGHT...A PURE NWFS WILL OCCUR ACROSS THE WESTERN NC MTNS 
THROUGH THE NIGHT. NAM INDICATES THAT NW WINDS WILL INCREASE TO 20 
TO 30 MPH WITH GUSTS BETWEEN 35 TO 40 MPH. FORECAST SOUNDINGS ACROSS 
THE SOUTHERN APPALACHIAN REGION INDICATES FAIRLY DEEP MOISTURE AND 
COLD TEMPERATURE PROFILES...EASILY MAINTAINING MOISTURE WITHIN -10C 
TO -18C RANGE FOR OPTIMAL SNOW DEVELOPMENT. THE STRONG LLVL FLOW AND 
COLD MOIST FLOW WILL SUPPORT A WIDE BAND OF CATE COVERAGE ACROSS THE 
MTNS THROUGH THE NIGHT. IT APPEARS THAT 1 INCH PER 3 HRS MAY 
CONTINUE ACROSS THE TN BORDER COUNTIES THROUGH THE NIGHT. MIN TEMPS 
ARE FORECAST TO RANGE FROM THE TEENS AND L20S ACROSS THE MTNS TO 
L20S EAST. WIND CHILL VALUES WILL LIKELY FALL TO 0 TO MINUS 5 ACROSS 
THE MTNS DURING THE PRE DAWN HOURS.

MONDAY...NWFS WILL CONTINUES ACROSS THE MTNS THROUGH THE DAY. 
HOWEVER...WRAP AROUND MOISTURE WILL BECOME INCREASINGLY SHALLOW AND 
NW WINDS WILL GRADUALLY WEAKEN. I WILL INDICATE A DECREASING TREND 
IN POPS AND QPF/SNOWFALL THROUGH THE DAY. HIGHS WILL REMAIN VERY 
COLD...WITH 20S ACROSS THE MTNS AND MID 30S EAST. SNOWFALL FROM 12Z 
SUNDAY UNTIL 0Z TUES MAY RANGE FROM A FOOT ACROSS THE HIGH 
ELEVATIONS TO SEVERAL INCHES ACROSS THE VALLEY FLOOR WITHIN BORDER 
COUNTIES. MONDAY NIGHT...SKY COVER WILL DECREASE SIGNIFICANTLY 
ACROSS THE CWA...LINGERING CLOUDS OVER THE UPSLOPE AREAS. FRESH SNOW 
COVER...CLEAR TO MOSTLY CLEAR SKY...AND DECREASING WINDS WILL 
SUPPORT LOW TO MID TEENS ACROSS THE MTNS AND UPPER TEENS TO L20S 
EAST.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 210 AM SATURDAY...THE ECMWF IS THE PREFERRED MODEL FOR THE 
MEDIUM RANGE AS THE GFS IS RATHER ERRATIC WITH THE DEVELOPMENT OF 
THE SYSTEM TOWARD WEEKS END.  TO START AT 12Z TUESDAY...THE 
ECMWF...GFS AND GEM ALL STOP NW FLOW SNOW FOR THE NC MOUNTAINS BY 
12Z TUESDAY.  HOWEVER...THE NAM HAS ITS LAST FRAME AT 12Z SHOWING 
WEAK NW FLOW SNOW FOR THE NORTHERN MOUNTAINS AND THE SREF ALSO HAS 
ITS LAST FRAME WITH APPARENT LAST HINT OF NW FLOW FOR NORTHERN 
MOUNTAINS.  WILL CONTINUE TO END NW FLOW AT 12Z WITH SURFACE HIGH 
PRESSURE AND SOME UPPER RIDGING BUILDING IN MID WEEK OVER OUR REGION.
THIS WILL RESULT IN WARMING TEMPERATURES AHEAD OF THE NEXT SYSTEM.

THE GFS IS FASTER IN SPREADING MOISTURE AND SCATTERED AREAS OF 
PRECIP WELL AHEAD OF THE ADVANCING COLD FRONT.  CLOUDS AND LIGHT 
PRECIP MOVES IN FROM THE WEST BY 00Z THURSDAY ON THE GFS FOR THE NC 
MOUNTAINS.  THE ECMWF STILL HAS IT OVER WESTERN TN AT THAT TIME.  I 
MAINTAINED A COMPROMISE BETWEEN THE GFS AND THE BETTER PERFORMING 
ECMWF.  THIS FORECAST LEANS TOWARD THE EC FOR CONSISTENCY BUT AT 
LEAST GIVES SOME CREDIT TO GFS.  BASED ON FORECAST 
SOUNDINGS...PRECIP WOULD LIKELY BEGIN AS -FZRA IF IT STARTS EARLY 
THURSDAY.  THE FREEZING PRECIP GOES AWAY FOR THE MOST PART AS STRONG 
SOUTHERLY FLOW OCCURS BRINGING TEMPERATURES TO A FEW DEGREES ABOVE 
NORMAL FOR FRIDAY AND MAYBE TEN DEGREES ABOVE NORMAL FRIDAY NIGHT.  
THE COLD FRONT WILL NOT REACH OUR WESTERN ZONES UNTIL SATURDAY NIGHT 
OR SUNDAY AS IT STANDS NOW. THE NEW 00Z SATURDAY ECMWF JUST CAME IN 
AND DOES TREND SOMEWHAT TOWARD THE GFS WHICH GIVES CREDENCE TO THE 
COMPROMISE. CERTAINLY NOT A WINTER STORM WITH THIS SYSTEM.

&&

.AVIATION /10Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...STILL EXPECTING JUST VERY LIGHT SOUTHERLY WINDS AND 
INCREASING HIGHER LVL CLOUDS THROUGH MID-MORNING SATURDAY. EXCELLENT 
AGREEMENT BETWEEN THE 18Z NAM/GFS AND 15Z SREF IN EXPANDING PLUME OF 
PCPN NORTHEAST TOWARD CLT FROM MID-MORNING ONWARD. THERMAL PROFILES 
INITIALLY ARE WARM ENUF TO SUPPORT LIQUID...BUT WITH THE COOLING 
COINCIDENT WITH HEAVIER PCPN...WOULD EXPECT A CHANGE TO ALL SNOW IN 
THE AFTERNOON WITH ALL THE ACCOMPANYING FLIGHT RESTRICTIONS. THERE 
IS ALSO SOME INDICATION THAT BANDED PRECIPITATION COULD AFFECT THE 
REGION IN THE LATE AFTERNOON AND EVENING...WHICH WOULD RESULT IN 
PERIODS OF HEAVY SNOW.

ELSEWHERE...HAVE GENERALLY FOLLOWED THE TREND ESTABLISHED ON THE 18 
UTC PACKAGE...INFERRING AN ENCROACHING/EXPANDING PCPN SHIELD 
AFFECTING ALL THE TERMINALS AS THE MORNING WEARS ON. LATEST GUIDANCE
EXPECTEDLY BULLISH ON AN ALL SNOW FCST FOR THE BALANCE OF THE DAY AS 
FLIGHT CATEGORIES TUMBLE INTO MVFR...AND THEN TO IFR BY LATE 
AFTERNOON AS THE SNOW BECOMES HEAVIER. AT KAVL THE TIMING WILL BE 3 
TO 5 HOURS EARLIER AS THE PCPN MOVES INTO THE MTNS BY MID MORNING.

OUTLOOK...LOW CIGS/VSBY SATURDAY AFTERNOON WILL GIVE WAY TO
SOME IMPROVEMENT EXPECTED SATURDAY NIGHT. HOWEVER...PERIODS OF MVFR 
CIGS/FLURRIES AS WELL AS GUSTY NW WINDS WILL BE POSSIBLE (ESP AT 
KAVL) LATE SAT NIGHT INTO SUNDAY. CONDITIONS WILL CONTINUE TO 
IMPROVE MONDAY INTO TUESDAY.

&&

.CLIMATE...
MAXIMUM CHRISTMAS SNOWFALL:

AT GREENVILLE-SPARTANBURG...2.0 INCHES IN 1947 AND 1909
                            1.0 INCHES IN 1962

IF WE DEFINE A WHITE CHRISTMAS AS HAVING AT LEAST ONE INCH OF SNOW 
ON THE GROUND DURING CHRISTMAS DAY...THEN THE YEAR 1962 WOULD NOT 
COUNT BECAUSE THE OBSERVED SNOW DEPTH WAS ONLY A TRACE BECAUSE THE 
SNOW MELTED AS IT FELL. HOWEVER...IN 1963 THERE WAS STILL AN INCH OF 
SNOW ON THE GROUND AT GSP FROM A STORM THAT MOVED THROUGH ON 
DECEMBER 23RD. THEREFORE...THE CLIMATE RECORD THAT DATES BACK TO 
1884 INCLUDES THREE INSTANCES OF A WHITE CHRISTMAS THAT WE KNOW 
OF...1909...1947...AND 1963. 

AT CHARLOTTE...5.8 INCHES IN 1947
               4.0 INCHES IN 1880
               0.2 INCHES IN 1909

IN THE AFOREMENTIONED 1963 EVENT...CHARLOTTE HAD ONE INCH OF SNOW ON 
THE GROUND ON 24 DECEMBER...BUT THAT SNOW MELTED TO A TRACE ON 
CHRISTMAS DAY. IN 1962...ONLY A TRACE OF SNOW FELL AT CHARLOTTE ON 
THE 25TH. IF THE 1909 EVENT DOES NOT COUNT BY DEFINITION...THAT 
LEAVES US WITH TWO INSTANCES OF A WHITE CHRISTMAS THAT WE KNOW OF... 
1880 AND 1947. THE CLIMATE RECORD FOR CHARLOTTE DATES BACK TO 1878.

AT ASHEVILLE...5.4 INCHES IN 1969
               3.4 INCHES IN 1947
               2.0 INCHES IN 1981
               0.4 INCHES IN 1993...1975...AND 1970
               0.3 INCHES IN 1962 AND 1915
               0.1 INCHES IN 1935 AND 1909

SINCE 1902...THERE HAVE BEEN SIX INSTANCES OF A WHITE CHRISTMAS AT 
ASHEVILLE. THERE WAS AT LEAST ONE INCH OF SNOW ON THE GROUND ON 
CHRISTMAS DAY IN 1947...1963...1969...1981...1993...AND 2009.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WINTER STORM WARNING UNTIL NOON EST SUNDAY FOR GAZ010-017.
     WINTER STORM WARNING FROM NOON TODAY TO NOON EST SUNDAY FOR 
     GAZ018-026-028.
     WINTER WEATHER ADVISORY FROM NOON TODAY TO NOON EST SUNDAY FOR 
     GAZ029.
NC...WINTER STORM WARNING UNTIL NOON EST SUNDAY FOR NCZ035-053-056-
     059-062>065-501>510.
     WINTER STORM WARNING FROM NOON TODAY TO NOON EST SUNDAY FOR 
     NCZ036-037-057-068>072-082.
     WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR NCZ033-048>052-
     058.
SC...WINTER STORM WARNING UNTIL NOON EST SUNDAY FOR SCZ001>003.
     WINTER STORM WARNING FROM NOON TODAY TO NOON EST SUNDAY FOR 
     SCZ004>010-012>014.
     WINTER WEATHER ADVISORY FROM NOON TODAY TO NOON EST SUNDAY FOR 
     SCZ011-019.

&&

$$
SYNOPSIS...DEO
NEAR TERM...MCAVOY
SHORT TERM...NED
LONG TERM...DEO
AVIATION...MCAVOY
CLIMATE...