FXUS61 KRLX 091846
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
145 PM EST WED DEC 9 2009
.SYNOPSIS...
STRONG COLD FRONT WITH STRONG AND GUSTY WINDS WILL MOVE THROUGH THE
REGION TODAY. COLDER WITH RAIN SHOWERS...CHANGING TO SNOW SHOWERS
TONIGHT. HIGH PRESSURE THURSDAY NIGHT AND FRIDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
LATE MORNING UPDATE...WELL DEFINED DRY SLOT WILL MOVE ACROSS THE
AREA TODAY...FOLLOWED BY STRONG WEST WINDS...IMPRESSIVE COLD
ADVECTION WITH FALLING TEMPERATURES...AND SCATTERED SHOWERS...IN THE
AFTERNOON. UPDATE WAS MAINLY TO INCREASE TEMPS AHEAD OF COLD
FRONT...LOWER SKY AND POPS IN DRY SLOT AHEAD OF FRONT.
PREVIOUS DISCUSSION...
WARM FRONTAL RAIN IN ASSOCIATION WITH POTENT STORM SYSTEM...CENTERED
OVER NW IL/EASTERN IA...CONTINUES ACROSS THE REGION THIS MORNING.
RAIN HAS BEEN HEAVY AT TIMES...WITH MANY LOCATIONS REPORTING 1 TO
1.5 INCHES OF RAIN IN THE LAST 12 HOURS. COLD FRONT ASSOCIATED WITH
THIS SYSTEM IS CURRENTLY DRAPED SOUTH FROM CENTRAL IN THROUGH
CENTRAL KY AND AREAS SOUTH...AND IS PROGGED TO MOVE INTO THE CWA
AROUND 12Z...AND EXIT AROUND 18Z. MUCH OF THE PRECIPITATION ACROSS
THE CWA APPEARS TO HAVE CHANGED TO RAIN TONIGHT DUE TO WAA AHEAD OF
THE FRONT...AND WILL PLAN TO ALLOW WINTER WEATHER ADVISORY FOR
RANDOLPH AND POCAHONTAS COUNTIES TO EXPIRE AT 4AM. STILL EXPECTING
STRONG WINDS TO DEVELOP ACROSS THE CWA TODAY AS TIGHT SURFACE
PRESSURE GRADIENT...IN COMBINATION WITH STRONG WINDS ALOFT...AFFECT
THE REGION. KRLX INDICATES WINDS IN THE FIRST FEW THOUSAND FEET
ABOVE THE SURFACE OF 50 TO 60 KTS. STRONGEST WINDS WILL OCCUR AFTER
COLD FRONT MOVES THROUGH REGION...AND WINDS ALOFT ARE ABLE TO MIX
DOWN TOWARDS THE SURFACE. ONLY MAJOR CHANGE MADE TO THE FORECAST
TODAY...WAS TO REMOVE MENTION OF THUNDER FROM THE FORECAST AS LATEST
SPC GUIDANCE INDICATES ONLY SHALLOW CONVECTION WILL BE LIKELY...AND
THAT CLOUD TOPS WILL NOT BE HIGH/COLD ENOUGH FOR CHARGE SEPARATION
TO OCCUR.
PRECIPITATION WILL GRADUALLY TAPER OFF ACROSS THE REGION TODAY AS
THE LOW CONTINUES TO MOVE OFF TO THE NORTHEAST...AND DRIER AIR WORKS
ITS WAY INTO THE REGION. COLDER AIR WILL FILTER INTO THE REGION
ON THE BACK END OF THE LOW. ANY LINGERING PRECIPITATION WILL CHANGE
TO SNOW OVERNIGHT...WITH ONLY LIGHT ACCUMULATIONS EXPECTED.
&&
.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
BIG WIND MAKER PULLS AWAY FROM THE AREA TONIGHT AND THURSDAY...WITH
UPPER FLOW GOING ZONAL AS IT WEAKENS A BIT...AND HEIGHTS GRADUALLY
RISE. SFC PRESSURE GRADIENT GRADUALLY SLACKENS AS INTENSE LOW
CENTER OVER LAKE SUPERIOR THIS EVENING SHIFTS E TO THE SAINT
LAWRENCE RIVER VALLEY BY THU EVENING. UPSLOPE SNOW SHOWERS SHOULD
ALSO DIMINISH DURING THIS TIME PERIOD AS THE FLOW WEAKENS. THE WSW
DIRECTION IS NOT THE MOST FAVORABLE UPSLOPE DIRECTION SO HAVE KEPT
SNOWFALL TOTALS ACROSS THE HIGH TERRAIN UNDER THREE INCHES.
HIGH PRESSURE SAILS ACROSS THE AREA FRIDAY INTO SATURDAY...WITH
MODELS NOT INDICATING THAT THE NEXT LOW PRESSURE SYSTEM...A SOUTHERN
STREAM FEATURE...DOES NOT IMPACT THE AREA UNTIL SATURDAY NIGHT.
WITH ONLY A WEAK UPPER LEVEL SHORT WAVE TROUGH INVOLVED...AND THE
SURFACE LOW CENTER ITSELF PASSING WELL SOUTH OF THE AREA...THE
PRECIPITATION ASSOCIATED WITH THIS SYSTEM WILL BE LIGHT...AND
BOUNDARY LAYER TEMPERATURES LIKELY ABOVE FREEZING DURING THE DAY.
CONTINUED UNDERCUTTING GUIDANCE THROUGH FRI WITH THE AIR MASS COMING
IN. USED LOW LEVEL MODEL DATA TAKING ADVANTAGE OF GOOD MIXING
BELOW H925 WED NT THROUGH THU...WHEN ANOTHER SHOT OF COLD ADVECTION
TAKES PLACE. AFTER A COLDER FRI NT PER STIFF ARMING OF WEEKEND
SYSTEM...FCST GETS CLOSER TO THE NUMBERS FOR HIGHS SAT AND LOWS SAT
NT.
&&
.LONG TERM /SUNDAY THROUGH TUESDAY/...
BUSY NEARLY ZONAL FLOW CONTINUES THROUGH THE PERIOD. MAIN CONCERN IS
OPPORTUNITY OF WINTRY MIX AGAINST THE EASTERN MOUNTAINS WITH WARM
AIR ADVECTION ON BACKSIDE OF HIGH SATURDAY NIGHT INTO SUNDAY.
ALSO...A POTENTIALLY STRONG COLD FRONT MAY PASS EARLY TUESDAY.
TREND IN MODELS IS TO SLOW DOWN WARM AIR ADVECTION PRECIPITATION
THAT COMES IN FROM THE SOUTH SATURDAY NIGHT INTO SUNDAY. ALSO
HOWEVER...MOST OF THE MOISTURE REMAINS TO OUR SOUTH. I WENT SLIGHTLY
BELOW HPC POPS TO ACCOUNT FOR THIS TREND. HOWEVER...COLD AIR DAMMING
ALONG THE EAST SLOPES OF THE WV MOUNTAINS...IS SUPPORTIVE OF
PROSPECT FOR POSSIBLE FREEZING RAIN THROUGH EARLY SUNDAY...WHILE
MOST OF THE REMAINDER OF THE AREA HAS PLAIN RAIN /PERHAPS A LITTLE
MIX IN THE NORTHERN LOWLANDS/. SO I HAVE ADDED ICE CHANCES TO THE
WEATHER GRIDS FOR THE AFFECTED AREAS. TEMPERATURES IN GENERAL WILL
BE COMPLICATED SATURDAY NIGHT...THAT IS...NON DIURNAL FOR MANY AREAS
DUE TO WARM AIR ADVECTION.
NEXT FEATURE OF INTEREST IS A COLD FRONT THAT LOOKS TO PASS THROUGH
SOMETIME IN THE LATE MONDAY NIGHT THROUGH TUESDAY MORNING TIME
FRAME. WENT ALONG WITH MID CHANCE RANGE FOR POPS...WITH MAINLY RAIN
ON FRONT END TRANSITIONING TO UPSLOPE SNOW FOR MAINLY THE MOUNTAINS
TUESDAY NIGHT INTO WEDNESDAY.
WHILE OPERATIONAL GFS AND ECMWF GENERALLY AGREE WITH THIS
SCENARIO...RUN-TO-RUN CONSISTENCY IS NOT GREAT AND THERE IS A FAIR
AMOUNT OF SPREAD IN THE ENSEMBLES. NOT SURE HOW AMPLIFIED THE
ASSOCIATED INCOMING TROUGH WILL BE...AND THE DEGREE OF COLD AIR
ADVECTION BEHIND THE FRONT INTO MIDWEEK. THE ONLY CERTAIN THING WILL
BE A STRONG TEMPERATURE GRADIENT FROM THE GREAT LAKES IN THE
NORTH...TO THE OHIO VALLEY IN THE SOUTH.
&&
.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
18Z WEDNESDAY THRU 18Z THURSDAY...
MAIN FEATURE IS THE STRONG WINDS EXPECTED AHEAD OF AND BEHIND COLD
FRONTAL PASSAGE TODAY. EXPECT SUSTAINED WINDS OF 20 TO 30KTS WITH
GUSTS OF UP TO 50 KTS. HIGHEST GUSTS/WINDS CAN BE EXPECTED OVER THE
HIGHER TERRAIN...WHERE GUSTS OF UP TO 60KTS CAN BE EXPECTED. WINDS
WILL SLOWLY DIMINISH THIS EVENING...BUT WILL STILL BE A FACTOR
THROUGH THE PERIOD.
COLD FRONT CURRENTLY MOVING ACROSS THE AREA THIS AFTERNOON...
EXITING THE MOUNTAINS OF WV BY 22Z. A LINE OF RAIN SHOWERS AND AN
ISOLATED THUNDERSTORM MAY ACCOMPANY THE FRONT...FOLLOWED BY WIDELY
SCATTERED TO SCATTERED POST FRONTAL RAIN SHOWERS. EXPECT MAINLY VFR
CEILINGS AROUND 3500 FEET...BUT OCCASIONAL MVFR CEILINGS IN
SCATTERED SHOWERS THIS AFTERNOON. ANY LINGERING RAIN SHOWERS WILL
BEGIN TO CHANGE OVER TO SNOW AFTER 21Z.
AFTER 00Z EXPECT MVFR/ISOLD IFR CONDITIONS IN SNOW SHOWERS...MAINLY
IN THE MOUNTAINS. ELSEWHERE MAINLY VFR CEILINGS.
AFTER 18Z THURSDAY...
WINDS WILL STILL BE MODERATE DURING THURSDAY. BRIEF IFR CONDITIONS
WILL BE POSSIBLE IN THE MOUNTAINS IN MORNING SNOW SHOWERS.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...WIND ADVISORY UNTIL 7 PM EST THIS EVENING FOR WVZ005>011-
013>020-024>032-039-040.
HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR WVZ033>038-
046-047.
OH...WIND ADVISORY UNTIL 7 PM EST THIS EVENING FOR OHZ066-067-075-
076-083>087.
KY...WIND ADVISORY UNTIL 7 PM EST THIS EVENING FOR KYZ101>103-105.
VA...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR VAZ003-004.
&&
$$
SYNOPSIS...TRM/SL
NEAR TERM...JMV
SHORT TERM...TRM
LONG TERM...MDP
AVIATION...JMV
