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...