FXUS63 KARX 090940
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
340 AM CST WED DEC 9 2009
.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
FORECAST CONCERNS THIS PACKAGE...WINTER STORM/BLIZZARD TODAY INTO
THIS EVENING...TEMPERATURES AND POTENTIAL NEED FOR WIND CHILL
ADVISORIES CENTERED ON THU/FRI MORNINGS.
SFC ANALYSIS AT 06Z HAD 986MB LOW OVER WEST CENTRAL IL...DEEPENING
AS IT MOVES NORTHEAST THIS MORNING. STRONGEST 3HR PRESSURE FALLS...
IN EXCESS OF 10MB...CENTERED ON MUSKEGON MI WITH AXIS OF STRONG
PRESSURE FALLS WEST TO LA CROSSE...AHEAD OF THE STRONG MID LEVEL
HGT FALLS. AREA RADARS SHOWED A BROAD AREA OF -SN TO +SN ACROSS THE
REGION IN STRONG LIFT/DEFORMATION BAND NORTH/NORTHWEST OF THE SFC-
MID LEVEL LOW. SNOWFALL RATES IN EXCESS OF ONE INCH/HR ACROSS MUCH
OF THE FCST AREA DURING THE 02Z-06Z TIME FRAME...WITH SNOWFALLS OF 4
TO 9 INCHES REPORTED AS OF MIDNIGHT. WV IMAGERY SHOWS IMPRESSIVE
NEGATIVE TILT TROUGH...AND LIFT AHEAD OF IT...LIFTING NORTHEAST
ACROSS THE MID/UPPER MS RIVER VALLEY. WINDS INCREASING ACROSS
WESTERN MN/IA AS THE LOW DEEPENS AND MOVES EAST OF THE AREA.
09.00Z NAM/GFS LOOK TO HAVE INITIALIZED VERY WELL AND OFFER VERY
SIMILAR SOLUTIONS FOR TODAY INTO FRI NIGHT. SOLUTIONS WELL
SUPPORTED BY LOCAL/REGIONAL WRF AND NON-NCEP MODELS AS THE INTENSE
LOW/WINTER STORM LIFTS THRU THE REGION EARLY IN THE PERIOD AND THE
SYSTEM REMAINS RATHER PROGRESSIVE. DPROG/DT OF 500MB HGTS AT 09.00Z
SHOWED NAM/GFS/ECMWF RUNS OF 07.00Z AND 08.00Z VERIFIED WELL ACROSS
NOAM/EASTERN PAC WITH BETTER CONSISTENCY TO ECMWF/GFS. MODELS REMAIN
VERY CONSISTENT THRU 36HRS AND CONTINUE TO CONVERGE ON A VERY TIGHT
COMMON SOLUTION AS THE INTENSE LOW/TROUGH LIFT THRU THE REGION TODAY
AND QUICKLY INTO EASTERN CAN BY 12Z THU. MODELS CONTINUE TO CONVERGE
ON A COMMON SOLUTION IN THE 36-84HR PERIOD AS THE BROAD CENTRAL/
EASTERN CONUS TROUGH LIFTS OUT AND FLOW TRANSITION TO BROAD WEST-
NORTHWEST/ZONAL ACROSS MUCH OF THE CONUS. MODELS FLATTER WITH THIS
FLOW BY 84HRS...FAVORING EARLIER ECMWF RUNS. CHECK OF OBS VS. MODEL
DATA AT 06Z SHOWED GFS WITH A BETTER SFC LOW STRENGTH/POSITION...NAM
A BIT TOO FAR EAST/SOUTH. A BLEND OF NAM/GFS LOOKED BEST WITH THE
00Z-06Z PRECIP/SNOW ACROSS THE REGION...WHICH GIVEN THE SNOW/WIND...
MANY OF THE AUTOMATED PRECIP GAUGES ARE NOT CATCHING ANYWHERE NEAR
ALL THE SNOW/LIQUID CONTENT. PER WV/REGIONAL RADAR IMAGERY...GFS
LOOKED BETTER WITH THE SHORTWAVE DETAILS IN THE APPROACHING TROUGH.
NAM APPEARED OVERDONE WITH A STRONGER SHORTWAVE NEAR KPDC. WITH
BETTER RUN-TO-RUN CONSISTENCY AND LOOKING BETTER ON SOME DETAILS AT
06Z...FAVORED GFS/ECMWF BLEND THIS CYCLE. THOUGH AGAIN...FAVORING
ANY ONE PARTICULAR DETERMINISTIC RUN WOULD HAVE MINIMAL IMPACT ON
THE SENSIBLE WEATHER THRU FRI NIGHT...EVEN AS THE MAJOR WINTER
STORM/BLIZZARD LIFTS ACROSS THE REGION. FORECAST CONFIDENCE REMAINS
GOOD/HIGH THIS CYCLE.
IN THE SHORT TERM...BY 12Z SFC LOW DEEPENS TO 979MB AND MOVES TO
JUST SOUTHEAST OF KMKE...THEN DEEPENS TO ABOUT 975MB AS IT LIFTS TO
CENTRAL LK HURON BY 00Z. 500MB TROUGH CLOSES OFF A CIRCULATION NEAR
KDVN AT 12Z...WHICH LIFT RAPIDLY EAST-NORTHEAST TODAY WITH WESTERLY
MID LEVEL FLOW ACROSS THE AREA BY 00Z. STRONG/DEEP LIFT NORTH OF THE
SFC/MID LEVEL LOW WILL CONTINUE ACROSS THE AREA THIS MORNING WITH
THE DEFORMATION BAND OF SNOW PIVOTING ACROSS THE AREA. SNOW FROM
THIS FORCING/LIFT WILL CONTINUE ACROSS THE AREA THRU MID MORNING...
THEN GRADUALLY TAPER TO -SN AS THE MID LEVEL TROUGH AXIS PASSES AND
DEEPER LIFT MOVE EAST. CONTINUE THE 100 PERCENT CHANCE OF SNOW
THIS MORNING. MODELS CONTINUE TO INDICATE SOME FN CONVERGENCE IN THE
900-700MB LAYER TO TRANSLATE EAST ACROSS THE AREA DURING THE
AFTERNOON. ENOUGH SO TO CONTINUE TO WRING OUT SOME -SN DURING THE
AFTERNOON...BUT ANY ADDITIONAL SNOW ACCUMULATIONS AFTER 18Z LOOK TO
BE QUITE LIGHT. LINGERING -SN CHANCE OVER NORTHEAST 2/3 OF THE FCST
AREA INTO THIS EVENING REASONABLE AS WELL WITH MOISTURE AND LOWER
LEVEL CYCLONIC FLOW/CONVERGENCE REMAINING OVER THE AREA. STILL
APPEARS TOTAL SNOW ACCUMULATIONS OF 11 TO 16 INCHES ARE LIKELY
ACROSS MOST OF THE FCST AREA BEFORE THE SNOW ENDS THIS AFTERNOON OR
EVENING.
AS THE SFC-850MB LOW CONTINUE TO MOVE EAST OF THE AREA EARLY THIS
MORNING...TIGHT PRESSURE GRADIENT AND COLD ADVECTION ON ITS WEST/
NORTHWEST SIDE WILL SPREAD EAST ACROSS THE AREA. WINDS OVER PARTS OF
SOUTHWEST MN/NORTHWEST IA GUSTING TO 45+KTS AS OF 0830Z...AND THIS
PRESSURE GRADIENT TO TRANSLATE EAST ACROSS THE AREA TODAY. AS THE
HEAVIER SNOW TAPERS OFF THIS MORNING...THE INCREASING WINDS WILL
BECOME THE BIGGER PROBLEM...CREATING CONSIDERABLE BLOWING/DRIFTING/
WHITE-OUTS THRU THE DAY INTO THIS EVENING. LEFT BLIZZARD WARNING AS
IS THRU THIS EVENING...THOUGH CONCERNED IT WILL BE DIFFICULT TO
REACH BLIZZARD CRITERIA EAST OF MS RIVER DUE TO THE TERRAIN AND MORE
TREE/FORECAST COVER. QUESTION OF BLIZZARD OR WINTER STORM WARNING
EAST OF MS RIVER...A FINE LINE TODAY AND PROBABLY BETTER TO ERR ON
THE SIDE OF CAUTION WITH THE BLIZZARD WARNING AS CONDITIONS WILL BE
EXTREMELY DANGEROUS/LIFE THREATENING TO BE STRANDED IN. BLIZZARD
WARNING LOOKS SOLID FOR ALL HIGHER TERRAIN AREAS WEST OF MS RIVER
TODAY.
VISIBILITY/CONDITIONS WILL IMPROVE THIS EVENING AS THE WIND
DIMINISHES AND THE SNOW ENDS. HOWEVER...GIVEN THE MAGNITUDE AND
AMOUNT OF SNOW TO BE MOVED...TRAVEL CONDITIONS LIKELY TO BE SLOW TO
IMPROVE.
AS PREVIOUS FORECAST STATED...LAST SLAP FROM THIS SYSTEM WILL BE
THE ARCTIC AIR POURING ACROSS THE REGION TONIGHT WITH TEMPS FALLING
TO NEAR/BELOW ZERO. THIS COUPLED WITH WINDS STILL IN THE 10-20/15-25
MPH RANGE AFTER MIDNIGHT/THU MORNING WILL SEND MANY WIND CHILLS TO
THE -20 TO -30 RANGE LATE TONIGHT/THU MORNING. WIND CHILL ADVISORY
WILL BE NEEDED FOR LATE TONIGHT/THU MORNING. TO AVOID CONFUSION...
WITH THE BLIZZARD WARNING ONGOING...WILL NOT ISSUE AN ADVISORY AT
THIS TIME. MAY ALSO NEED A WIND CHILL ADVISORY FOR LATE THU
NIGHT/FRI MORNING WITH WIND CHILLS IN THE -15 TO -25 RANGE. WILL
HANDLE THIS ONCE THE BLIZZARD/WINTER STORM PORTION WINDS DOWN.
OTHER THAN THE WIND CHILLS...QUIET WEATHER EXPECTED THU THRU FRI
NIGHT AS FLOW FLATTENS/HGTS SLOWLY RISE AND HIGH PRESSURE BUILDS
INTO/ACROSS THE REGION. TEMPS TO MODERATE A BIT FRI/FRI NIGHT AS
LOWER LEVEL WARM ADVECTION SPREADS ACROSS THE REGION.
WITH ABUNDANT FRESH SNOW COVER...COLDER OF GUIDANCE HIGHS LOWS
PREFERRED FOR TODAY THRU FRI NIGHT.
.LONG TERM...SATURDAY THROUGH TUESDAY
09.00Z MEDIUM RANGE MODELS IN RATHER GOOD AGREEMENT WITH EACH OTHER
AND THEIR PREVIOUS RUNS FOR SAT/SUN AS FLOW BECOMES NEARLY ZONAL
ACROSS THE NORTHERN CONUS. MODELS STARTING TO SHOW SOME CONSISTENCY
FOR A SHORTWAVE TO MOVE ALONG THE US/CAN BORDER FOR LATER SUN/SUN
NIGHT...WITH LOW PRESSURE DEVELOPING INTO THE CENTRAL NORTHERN
PLAINS. STRONGER LOW LEVEL WARM ADVECTION AHEAD OF IT SPREADS ACROSS
THE AREA SAT-SUN...WITH SOME MOISTURE ARRIVING SUN. RAISED HIGHS/
LOWS A BIT FOR SAT THRU SUN NIGHT WITH THE INCREASING MODEL SIGNAL
FOR THE WARM ADVECTION AND ADDED A SMALL -SN CHANCE TO SUN. MODELS
DIFFER ON SHORTWAVE TIMING/STRENGTH DETAILS BY MON/TUE AS THE FLOW
LOOKS TO BUCKLE/RE-AMPLIFY ACROSS NOAM. WITH CONFIDENCE WANING BY
MON/TUE LEFT MON/TUE GRIDS AS IS BUT MAY YET NEED A SNOW CHANCE FOR
MON.
&&
.AVIATION...TODAY AND TONIGHT
AIRPORT OPERATIONS AND AIR TRAFFIC TO SEE MAJOR IMPACTS OVER THE
NEXT 24 HOURS AS MAJOR WINTER STORM/BLIZZARD TRAVERSES THE REGION.
DEEP SURFACE LOW OVER NORTHERN ILLINOIS EARLY THIS MORNING WILL
CONTINUE TO LIFT NORTHEASTWARD TODAY AND BE LOCATED IN NORTHERN
LOWER MICHIGAN BY MIDDAY. LARGE AREA OF MODERATE TO HEAVY SNOW HAS
OVERSPREAD THE REGION...INCLUDING BOTH TAF SITS. WIDESPREAD LIFR
CONDITIONS CURRENTLY OVER THE SITES WILL CONTINUE THROUGH AT LEAST
18Z TODAY. NORTH WINDS HAVE ALREADY INCREASED WITH GUSTS OF 25 TO 30
KNOTS AT KRST AND THESE WINDS WILL CONTINUE TO INCREASE WITH GUSTS
TO 30 TO 40 KNOTS LIKELY AT BOTH TAF SITES THROUGH MUCH OF THE DAY.
THE SNOW WILL BEGIN TO TAPER OFF THIS AFTERNOON...BUT BLOWING AND
DRIFTING OF THE SNOW WILL CONTINUE TO RESULT IN VISIBILITY
RESTRICTIONS. IMPROVEMENT LOOKS TO COME AFTER 10.00Z AS WINDS
SUBSIDE A LITTLE AND CEILINGS/VISIBILITIES LIFT INTO THE MVFR
CATEGORY.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...BLIZZARD WARNING UNTIL MIDNIGHT CST TONIGHT FOR WIZ017-
WIZ029-WIZ032-WIZ033-WIZ034-WIZ041-WIZ042-WIZ043-WIZ044-
WIZ053-WIZ054-WIZ055-WIZ061.
MN...BLIZZARD WARNING UNTIL MIDNIGHT CST TONIGHT FOR MNZ079-
MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.
IA...BLIZZARD WARNING UNTIL MIDNIGHT CST TONIGHT FOR IAZ008-
IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-IAZ029-IAZ030.
&&
$$
SHORT/LONG TERM...RRS
AVIATION..........RABERDING
