FXUS63 KARX 082038
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
240 PM CST TUE DEC 8 2009

.SHORT TERM...TONIGHT THROUGH FRIDAY

FORECAST CONCERNS...AS THEY WERE THE PAST SEVERAL DAYS...CONTINUE TO 
LASER IN ON THE ON GOING WINTER STORM AND ITS VARIETY OF IMPACTS ON 
THE FORECAST AREA.

PREVIOUS FORECAST DISCUSSIONS COULD PROBABLY BE CUT AND PASTED INTO 
THIS DISCUSSION...AS THE CONSISTENCY OF THE MODELS...WITHIN AND 
COMPARED TO EACH OTHER...CONTINUES OUTSTANDING. 

CURRENT SNOW ACROSS THE REGION...PER 88-D RADAR IMAGERY...BEING 
MOSTLY DRIVEN BY ISENTROPIC UPGLIDE AND WARM AIR ADVECTION IN THE 
LOW LAYERS. MEANWHILE...AN UPPER LEVEL SHORTWAVE TROUGH WAS SLIDING  
INTO THE SOUTHERN PLAINS...WILL DRIVE NORTHEAST INTO THE GREAT LAKES 
ON WED. THE SFC LOW WITH THIS EVOLVING STORM WILL TAKE THE SAME 
TRACK...CENTERED AROUND THE SOUTHERN TIP OF LAKE MICHIGAN BY 12Z 
WED. 08.12Z GFS AND NAM ARE IN GREAT AGREEMENT HERE...WITH ONLY A 2 
MB DIFFERENCE. AGAIN...ITS A BROKEN RECORD...BUT ALL THE MODELS HAVE 
BEEN PAINTING THIS STORM TRACK FOR AT LEAST THE PAST 4 DAYS...WITH 
ONLY SMALL CHANGES THAT WOULD HAVE HAD LITTLE IMPACT ON THE SENSIBLE 
WEATHER FOR THE LOCAL AREA. THIS SYSTEM BOMBS AS IT MOVES IN...WITH 
SFC PRESSURES PROGGED TO DROP FROM 995 AT 00Z TONIGHT...TO 975 BY 
12Z WED. THIS INCREASING PRESSURE GRADIENT WILL RESULT IN VERY 
STRONG AND GUSTY WINDS DEVELOPING OVERNIGHT...CONTINUING THROUGH 
MUCH OF WEDNESDAY. THIS TURNS THIS WINTER STORM FROM AN ALREADY 
SIGNIFICANT STORM DUE TO THE HIGH AMOUNTS OF SNOW EXPECTED...TO A 
HIGH IMPACT...VERY DANGEROUS STORM FROM THE BLOWING/DRIFTING/REDUCED 
VISIBILITY ASPECT BY ADDING THE WIND WITH THE SNOW.

THIS IS THE KIND OF STORM WHERE FATALITIES OCCUR IF PRECAUTIONS ARE 
NOT TAKEN.

LOOKING AT SOME OTHER FORCING MECHANISMS...THIS WINTER STORM WILL BE 
PUSHED ALONG BY A 120+ KT 300 MB JET...WHICH WILL ENHANCE THE 
AVAILABLE LIFT TONIGHT. QG CONVERGENCE IS STRONG THROUGH THE 
LAYERS...MAXIMIZED FOR THE FORECAST AREA BETWEEN 00-12Z. PV 
ADVECTION WITH THE STORM IS MAXED AT 06Z LOCALLY AND A NORTH-SOUTH 
RUNNING TIME/HEIGHT X-SECTION SHOWS THE 2-D FRONTOGENETIC RESPONSE 
STILL SLOPING ACROSS THE FORECAST AREA THROUGH 18Z WED. ALL ABOUT 
THE SAME AS THE MODELS HAVE BEEN DEPICTED. THERE HAVE BEEN SOME 
CHANGES THOUGH...WHICH COULD INDICATE EVEN HIGHER SNOW TOTALS. THE 
12Z MODELS ARE SHOWING MORE THETA-E AIR...RICH IN 
MOISTURE...WRAPPING AROUND THE SYSTEM...INTO THE DEFORMATION AREA. 
THIS COULD LEAD TO THE ACCUMULATING SNOWS LINGERING LONGER ON 
WED...WITH HIGHER AMOUNTS AFTER 12Z. THE FAVORABLE DENDRITIC GROWTH 
ZONE HAS INCREASED IN DEPTH...WHICH WOULD SUPPORT HIGHER SNOW 
RATIOS. COBB OUTPUT VIA THE GFS AND NAM HAVE INCREASED FROM AN 
AVERAGE OF 14:1 FOR THE PAST FEW DAYS...TO CLOSER TO 18:1 TONIGHT 
THROUGH WED. BELIEVE THIS LOOKS REASONABLE...AND WILL BE INCREASING 
SNOW TOTALS A BIT. 

AS MENTIONED...THE ADDITION OF THE STRONG/GUSTY WINDS IS WHAT WILL 
SEPERATE THIS STORM FROM BEING A SIGNIFICANT SNOW PRODUCER...TO ONE 
WHERE WHITE-OUT CONDITIONS ARE COMMON AND THE POTENTIAL FOR WEATHER 
RELATED FATALITIES ARE HEIGHTEN. THIS IS A VERY DANGEROUS 
STORM...AND THAT CANNOT BE OVERSTATED. 

SHIFTING THE FOCUS TO THE WIND...AGAIN...PRESSURE GRADIENT TIGHTENS 
AS THE BOMBING SYSTEM APPROACHES. NORTHWEST WINDS WILL INCREASE TO 
20 TO 30 MPH OVERNIGHT TONIGHT...WITH GUSTS UP TO 40 MPH. WOULDN/T 
BE SURPRISED IF THE OPEN/UNSHELTERED AREAS OF SOUTHEAST MN/NORTHEAST 
IA EXPERIENCE WINDS OF 25 TO 35 MPH...GUSTS TO 45 MPH...ON WED 
MORNING. WITH ABOUT 8 INCHES OF FRESH...POWDERY SNOW BY THE TIME THE 
STRONGEST WINDS KICK IN...WITH AN ADDITIONAL SEVERAL INCHES OF SNOW 
FALLING...THERE WILL BE SIGNIFICANT BLOWING AND DRIFTING. 
VISIBILITIES WILL BE REDUCED TO UNDER 1/4 MILE AT TIMES...AND 
WHITE-OUT CONDITIONS APPEAR VERY LIKELY IN THE WINDIER AREAS...IF 
NOT ALL OF THE FORECAST AREA...FROM LATE TONIGHT INTO EARLY WED 
AFTERNOON. 

WILL ALL THIS IN MIND...HAVE UPGRADED THE WINTER STORM WARNING TO A 
BLIZZARD WARNING...WHICH WILL ALSO BE IN EFFECT UNTIL 06Z THU. 
SO...THE ENTIRE FORECAST AREA IS NOW UNDER A BLIZZARD WARNING.

LASTLY...HAVEN/T TOUCHED ON THE DANGEROUS WIND CHILLS THAT ARE 
EXPECTED ON THE BACKSIDE OF THIS SYSTEM. LOTS OF COLD AIR MOVES IN 
ON WED AS THE STORM SYSTEM PULLS NORTHEAST. COUPLE THIS WITH WINDS 
OF 15 TO 20 MPH...AND WIND CHILLS OF 20 TO 25 BELOW ZERO ARE 
ANTICIPATED BY 12Z THU. A PARTING SLAP FROM THIS 
DANGEROUS...POTENTIALLY DEADLY WINTER STORM. AFTER THE WARNING 
EXPIRES...A WIND CHILL ADVISORY MIGHT BE NEEDED FOR THU MORNING. 

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY

MODELS IN GENERAL AGREEMENT WITH THE OVERALL UPPER LEVEL FLOW 
BECOMING ZONAL FOR THE WEEKEND INTO EARLY NEXT WEEK. SOME 
DIFFERENCES IN HOW THEY HANDLE VARIOUS PERTURBATIONS TO MOVE ALONG 
THE FLOW THOUGH...LOWERING FORECAST CONFIDENCE A BIT. THE GFS AND 
ECMWF BOTH WANT TO BRING A WEAK SHORTWAVE TROUGH TOWARD THE REGION 
BETWEEN 00-12Z MON...THEN DROP A STRONGER SHORTWAVE TROUGH OUT OF 
CANADA AND ACROSS THE UPPER MISSISSIPPI RIVER VALLEY BY 12Z TUE. THE 
MODELS PRODUCE MORE QPF WITH THE SUN NIGHT SYSTEM...HAVING MORE 
SATURATION...COMPARED TO THE POTENTIAL SHORTWAVE FOR TUE. WILL 
LIKELY SIDE TOWARD HPC GUIDANCE FOR PCPN CHANCES IN THESE PERIODS. 
WHILE THERE IS SOME INDECISION ON THE PCPN POSSIBILITIES...WHAT DOES 
LOOK CERTAIN IS THAT IT WILL BE COLD. TEMPERATURES WILL TUMBLE 
BEHIND THE WINTER STORM...AND COLD CONDITIONS WILL PERSIST THROUGH 
THE WEEKEND. SOME SLIGHTLY WARMER AIR LOOKS LIKE IT MAY MOVE BACK 
INTO THE REGION FOR THE START OF THE NEW WORK WEEK.

&&

.AVIATION...

AIRPORT OPERATIONS AND AIR TRAFFIC TO SEE MAJOR IMPACTS THE NEXT 
24-36 HOURS AS MAJOR WINTER STORM/BLIZZARD TRAVERSES THE REGION. 

BROAD AREA OF SNOW ALREADY UNDERWAY WELL AHEAD OF THE MAIN SYSTEM AS 
ADVECTION OF MOIST AIR LIFTED OVER THE COLD AIR ALREADY IN PLACE. 
MAY HAVE A FEW HOURS THIS EVENING BEFORE WE DETERIORATE TO IFR/LIFR 
CONDITIONS. 

MODELS REMAIN IN EXCELLENT AGREEMENT...AND ALL SHOW FRONTOGENETIC 
BANDING WITHIN THE MAIN LIFT AREA. SIGNIFICANT SNOWFALL OF UP TO 
10-14 INCHES ANTICIPATED FOR BOTH TAF LOCATIONS BY MID-DAY 
WEDNESDAY. BUT ADDING TO THE TURMOIL WILL BE THE STRONG WINDS AS THE 
SYSTEM CONTINUES TO RAPIDLY DEEPEN AS IT TRACKS FROM WESTERN KANSAS 
UP TOWARD CHICAGO. INCREASED EXPECTED WIND SPEEDS IN THE 18Z TAFS 
WITH G45KT AT KRST IN THE OPEN AREA. MAY NOT BE QUITE AS GUSTY AT 
THE KLSE TAF LOCATION...BUT WITHIN THE VICINITY FOR SURE. 

SNOW WILL TAPER OFF WEDNESDAY AFTERNOON/EVENING...BUT WINDS WILL 
HOWL THROUGH THE DAY. NOT ONLY WILL AIRCRAFT OPERATION BE 
DIFFICULT...BUT OVERALL AIRPORT OPERATIONS WILL BE SEVERELY AFFECTED 
AS WELL. BLOWING AND SEVERE DRIFTING WILL BE DIFFICULT TO CONTEND 
WITH. 

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR WIZ017-
     WIZ029-WIZ032-WIZ033-WIZ034-WIZ041-WIZ042-WIZ043-WIZ044-
     WIZ053-WIZ054-WIZ055-WIZ061.

MN...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR MNZ079-
     MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.

IA...BLIZZARD WARNING UNTIL MIDNIGHT CST WEDNESDAY NIGHT FOR IAZ008-
     IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-IAZ029-IAZ030.

&&

$$

SHORT/LONG TERM... RIECK
AVIATION.......... MW