FXUS61 KRLX 051057
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
556 AM EST SAT DEC 5 2009
.SYNOPSIS...
SURFACE LOW HEADS UP COAST...WHILE UPPER LEVEL WAVE PASSES THROUGH
WITH SNOW FOR MUCH OF AREA...TODAY. HIGH PRESSURE SUNDAY...THEN
WEAK COLD FRONT MONDAY. STRONGER SYSTEM MIDWEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
RARE SYNOPTIC SCALE SNOW EVENT SETTING UP ACROSS AREA EARLY THIS
MORNING. THIS IS LARGELY AN UPPER LEVEL-DRIVEN EVENT WITH
BAROCLINIC LEAF CLEARLY APPARENT VIA BACK EDGE OF COLD CLOUD TOPS
DOWN THROUGH TN VALLEY AS OF 09Z. THIS QUICK MOVING SYSTEM WILL BE
OUT OF THE AREA ALMOST ENTIRELY BY 00Z SUN...RATIONALIZING A NON
SECTORIZED ADVISORY WITH A COMMON 00Z END TIME FOR ALL THOUGH IT
WILL QUIT EARLIER SW.
SUPPORT COMES MAINLY FROM UPPER DIV/LOW LEVEL CON COUPLET /INVERTED
TROUGHS/ ENHANCED ON WESTERN EDGE BY MID LEVEL DEFORMATION AND
THROUGHOUT VIA DIFFERENTIAL CYCLONIC VORTICITY ADVECTION ALONG WITH
SLIGHT ISENTROPIC LIFT. MODELS INDICATE DEEP SATURATION THROUGH
HEIGHT OF EVENT WHICH IS THIS MORNING THROUGH EARLY AFTERNOON. THIS
FAVORS GOOD ICE CRYSTAL GROWTH AND ENHANCED SNOW TO LIQUID RATIOS.
OUTPUT OF CARIBOU TOOL SHOWS A NNE-SSW AXIS OF RATIOS CLOSE TO 20:1
NEAR OHIO RIVER THIS MORNING MOVING E ACROSS FCST AREA DURING
AFOREMENTIONED TIME PERIOD.
WITH QPF OUTPUT CLOSE AMONG THE MODELS...USED DETAIL OF NAM12 FOR
QPF. THEN USED MODIFIED CARIBOU OUTPUT FOR SNOWRATIO * QPF TO
ARRIVE AT SNOW AMOUNTS. CATEGORICAL POPS THROUGHOUT WV AND SW VA
ALONG WITH QPF OUTPUT FROM TWO TENTHS W TO FOUR TENTHS E WITH
AFOREMENTIONED TOOL YIELDS SNOWFALL VALUES OF 2 TO 3 INCHES ACROSS
LOWLANDS AND 4 TO 6 INCHES IN THE MTNS WARRANTS SIGNIFICANT
EXPANSION OF THE ADVISORY TO NOW INCLUDE MOST OF OUR WV COUNTIES.
GIVEN MUCH LOWER DEW POINTS TOWARD THE OHIO RIVER ALONG WITH
ENHANCED SUPPORT THERE...ONCE I EXPANDED ADVISORY W OUT OF THE
MTNS...IT APPEARED NECESSARY TO TAKE IT AT LEAST CLOSE TO THE OHIO
RIVER.
06Z NAM12 SUPPORTS ITS PREDECESSOR IN DEPICTING FIRST WIDESPREAD
ACCUMULATING SNOW EVENT OF THIS YOUNG WINTER SEASON OF 2009-2010.
FINAL QUESTION IS THE TEMPERATURES...WHICH WERE STILL INCHING
SLIGHTLY UPWARD EARLY THIS MORNING ON ACCOUNT OF THICKENING
CLOUDINESS...BUT WILL SETTLE BACK ON ONSET OF SNOW AND BE HELD THERE
DURING SNOWFALL WITH WEAK COLD ADVECTION AND OF COURSE THE SOLID
OVERCAST THIS DECEMBER DAY. THIS PUTS VALUES BELOW ALBEIT NEAR
FREEZING THROUGHOUT THE EVENT WITH WEAK DECEMBER INSOLATION THROUGH
THE THICK CLOUD. THIS PUTS HIGH TEMPERATURES CLOSEST TO THE LOWER
MAV AND SUPPORTS REALIZATION OF THE AFOREMENTIONED ACCUMULATION
POTENTIAL AT LEAST OFF TREATED ROADS.
GROUND TEMPERATURES REMAIN IN THE MID 40S 4 INCHES DEEP BUT SHOULD
BE MUCH CLOSER TO FREEZING RIGHT AT THE SURFACE GIVEN AIR
TEMPERATURES NOT FAR ABOVE FREEZING PAST 24 HOURS AND AT OR BELOW
FREEZING OVERNIGHT.
SYSTEM PULLS AWAY TONIGHT WITH UPSLOPE SNOW LINGERING IN THE
MOUNTAINS. ACCUMULATION THERE TONIGHT SHOULD BE QUITE MINIMAL WITH
MOIST LAYER PRETTY MUCH BELOW H85 AFTER 00Z SUN. TEMPERATURES WERE
WELL CLUSTERED FOR LOWS TONIGHT...WELL BELOW FREEZING. THIS WILL
RESULT IN ICY PATCHES ON ROADS INCLUDING BLACK ICE.
&&
.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
SHOULD BE A DECENT DAY ON SUN WITH ONLY MID/HIGH CLDS AS FLOW TURN
SW AND WAA COMMENCES AHEAD OF NEXT S/W TROF. THIS TROF WILL PASS
NORTH OF CWA INTO AREA OF CONFLUENCE...WITH A WEAK FRONT PASSING
THROUGH ON MONDAY. LEFT SCHC POPS IN FOR THIS. TEMP PROFILES
INDICATED THERE COULD BE SOME WET SNOW IN ANY PCPN MON SE OH...WITH
SHRA BY THE TIME IT REACHES KANAWHA VALLEY. COULD BE A FEW UPSLOPE
-SHSN IN THE MTNS MON NIGHT....HOWEVER POOR SETUP WITH RESPECT TO
FLOW/MOISTURE WARRANTS ONLY SCHC POPS.
SFC HIGH WILL BRIEFLY BUILD IN FOR TUES. HOWEVER...CIRRUS WILL
ALREADY BE STREAMING IN FROM THE SW AS NEXT SYS BEGINS TO TAKE SHAPE
OVER THE CENTRAL PLAINS.
MODELS ARE IN GOOD AGREEMENT WITH THE EVOLUTION AND TIMING OF THIS
SYS. THE 00Z RUNS OF GFS/ECWMF/GEM-NHEM ALL AGREE ON EJECTING A NEG
TILT TROF INTO THE EASTERN CONUS BY WED. ASSOCIATED SFC LOW TO BE
DEEPENING AS IT TRACKS THROUGH THE WESTERN OH VALLEY BY 12Z WED.
WITH SUCH A STRONG SYS TRACKING WELL WEST OF THE AREA...ONE WOULD
EXPECT A MOSTLY RA SITUATION. HOWEVER...SECONDARY CYCLOGENESIS
SHOULD ALSO BE OCCURRING SOMEWHERE OVER THE MID ATLANTIC REGION AND
MODELS ARE ALL IN AGREEMENT ON THIS. AS A RESULT LOW LEVEL COLD AIR
SHOULD MANAGE TO HANG ON LONGER...ESPECIALLY ACROSS THE NORTHERN
MTNS/EASTERN SLOPES.
LOOKING AT THE TEMP PROFILES...IT APPEARS A DEEP ENOUGH COLD LAYER
WILL EXIST FOR PCPN TO BEGIN AS MOSTLY SN ACROSS THE NORTHERN
MTNS/EASTERN SLOPES TUE NIGHT...WITH A BRIEF MIX OF SLEET/SN/ZR
ACROSS THE NORTH AND MOSTLY RAIN NE KY/KANAWHA VALLEY/SW VA. STRONG
WAA WILL SEND MOST PLACES TO LIQUID BY 12Z WED. EXCEPTION BEING
EASTERN SLOPES OF NORTHERN MTNS...WHERE SECONDARY CYCLOGENESIS ALONG
MID ATLANTIC COAST WILL KEEP A NE FLOW...WITH ZR BECOMING MORE OF A
THREAT. WIND WILL ALSO BE A CONCERN ACROSS THE SOUTHERN
MTNS...COURTESY OF 70 KT H85 FLOW FEEDING IN OFF THE ATLANTIC.
BUMPED UP WINDS AFOREMENTIONED AREA TO NEAR 30KTS BY DAWN WED.
PLAYED UP WORDING IN RWS FOR WIND AS WELL AS THE WINTER WX THREAT.
ALSO MENTIONED IN HWO FOR THE NORTHERN MTNS FOR FRZ PCPN. CURRENT
INDICATIONS ARE THAT THIS COULD BE A RATHER SIGNIFICANT WINTER WX
EVENT FOR THE NORTHERN MTNS.
FOR TEMPS...LATEST GUIDANCE IN GOOD AGREEMENT WITH TEMPS THROUGH
MON...AND ONLY MINOR TWEAKING WAS PERFORMED. RAN A NON DIURNAL TRACE
REST OF THE WAY. THIS RESULTED IN AN EARLY LOW TUE NIGHT...BEFORE
WAA COMMENCES IN EARNEST WITH CLIMBING TEMPS OUTSIDE OF THE NORTHERN
MTNS INTO THE 40S BY DAWN WED. TEMPS ONLY WARM TO NEAR FRZ EASTERN
SLOPES.
&&
.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
MODELS IN FAIRLY DECENT AGREEMENT WITH GENERAL PATTERN THROUGH THIS
PERIOD. WILL FOLLOW A BLEND OF THE ECMWF AND ECMWF ENSEMBLE.
TEMPERATURES ARE MARGINAL MONDAY NIGHT BEHIND A COLD FRONT FOR
UPSLOPE SNOW SHOWERS. WILL CONTINUE WITH JUST A VERY SMALL POP. A
STRONG SYSTEM THEN MOVES UP WEST OF THE REGION TUESDAY NIGHT AND
WEDNESDAY...PROVIDING A DECENT SHOT OF RAIN. BEHIND THE
SYSTEM...MODELS SHOW A GOOD UPSLOPE SNOW EVENT. IF MODELS HANG ON TO
THIS SOLUTION...EVEN THE LOWLANDS COULD SEE SOME ACCUMULATIONS.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
RARE WIDESPREAD STEADY SNOW EVENT...MAINLY E OF THE OHIO RIVER...
WITH WIDESPREAD IFR CONDITIONS TODAY...EVEN LIFR AT TIMES IN AND
NEAR THE MOUNTAINS. CONDITIONS IMPROVE LATER TODAY FROM W TO
E...WITH CLEARING TONIGHT FROM W TO E.
NOTHING MORE THAN MVFR MIST...HAZE...OR SMOKE FROM BURNING WOOD...IN
THE VERY COLD AIR NEAR DAWN SUNDAY.
LIGHT N TO NE FLOW TODAY WILL BECOME NW LATE TODAY AND THEN CALM
LATE TONIGHT. LIGHT N FLOW ALOFT TODAY BECOMES LIGHT TO MODERATE NW
FLOW TONIGHT.
AFTER 12Z SUNDAY...
IFR IN RAIN POSSIBLE TUESDAY NIGHT INTO WEDNESDAY.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR WVZ008-
013>020-024>040-046-047.
OH...NONE.
KY...NONE.
VA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ003-
004.
&&
$$
SYNOPSIS...TRM/30
NEAR TERM...TRM
SHORT TERM...30
LONG TERM...RPY
AVIATION...TRM
