542 
FXUS63 KARX 012139
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
339 PM CST Sun Jan 1 2023

.DISCUSSION...(This evening through Sunday)
Issued at 300 PM CST Sun Jan 1 2023

Key Messages: 

 - A complex Midwest winter storm continues to bring an array of
   wintry weather to the region (snow, freezing rain, mix & rain)
   Monday night through Tuesday with lingering snow Wednesday 
   morning.

 - Main freezing rain impacts occur Monday night from around
   Charles City, IA to Mauston. With the warm air moving into the
   system and how far north and west uncertain how far east the
   heavier ice accumulations will be. Converted the winter storm 
   watch to an ice storm warning in the west and added Chickasaw 
   Co. to the winter storm watch.

 - The heavy snow band sets up from southwest MN to northern WI,
   however this band has been waffling north and south. Snow
   expected to spread southeast through Wednesday with the upper
   low.

 - Areas of Fog Tonight/A Light Wintry Mix Monday

Areas of Fog Tonight:

The SREF continues to indicate that there will be areas to 
widespread fog along and north of a cold front tonight. The highest 
probabilities of fog will be along and north of Interstate 94. This 
fog will likely reduce visibilities to less than a mile. There may 
be even some localized dense fog.

A Light Wintry Mix Monday

There will be 2 areas of strong frontogenesis across the area from 
late Monday morning into the afternoon. The northern area is located 
along and north of Interstate 90. This 800-500 mb frontogenesis is 
located along a stationary cold front. Further south, there will be 
a band of 900-800 mb frontogenesis (associated with a warm front) 
moving north across eastern Iowa and northern Illinois. Dry easterly 
flow will initially inhibit the development of precipitation. The 
northern band of precipitation will be mainly snow. Snow amounts 
will range from a trace to a few tenths of an inch. Meanwhile, 
further south, soundings show that a combination of a dry layer and 
warm nose will greatly limit ice seeding from aloft. As a result, 
the precipitation will be either light rain or light freezing rain 
during the mid to late afternoon.

Overview Monday Night through Tuesday:

A longwave trough over the Sierras/Rockies is forecast to organize 
over the Four Corners region and continue over the Rockies into the 
Plains Monday night. A 120kt jet over the Great Lakes is exiting the 
area, in addition, a 110kt across western Kansas is lifting north 
into the region. A coupled jet is inducing broad upper level 
divergence from the Dakotas into MN and WI Monday and broad synoptic 
lift.  The shortwave moving across southern Canada is playing a role 
with drier low and mid levels that will need to be overcome.  Also, 
the next trough tracking across southern Canada will affect the snow 
band that develops out of the Plains. Deep moisture with 1.5 inch 
precipitable water values emerge across parts of eastern TX/LA/AR 
Monday and with strong moisture transport north and east. PWAT 
values increase 00-06Z to around 1" across parts of Iowa and 
northern Illinois.  Parts of the local area are in the transition 
zone between the rain, freezing rain, sleet, and snow lending to an 
area of freezing rain. As the moisture is drawn northward and the 
cold conveyor belt transports this moisture north and west, heavy 
snow across the Plains continues across the Upper Mississippi Valley 
(MN/WI) Tuesday northwest of the surface low tracking from Iowa 
toward Michigan within the deformation band. The extent and location 
of the dry slot limits the heavy snow band farther south, however 
narrow heavier snow bands can set up as the trough continues to 
track over the area due to embedded frontogenetic/steep lapse rate 
areas.

Anomalously High Precipitable Water Values: 

The 01.00Z NAEFS show PWAT values of 4.0 to 4.5 standard deviations 
above normal toward Grant County and 2 to 4 SDs across the rest of 
the forecast area. These are in the 99.5 percentile.  The 01.00Z EC 
Extreme Forecast Index (EFI) is slightly lower than yesterday with 
89% of the ensembles showing a higher QPF event and the shift of 
tails around 1 instead of 1 to 2 for and extreme event across parts 
of southern MN into northern WI. 

Freezing Rain: 

The medium range model solutions continue to show a band of 
freezing rain developing late Monday afternoon through Monday 
night. Forecast soundings continue to show a significant warm 
nose developing as the surface low tracks from Kansas toward 
central Iowa. With temperatures remaining below freezing the 
potential heavy icing is looking more likely. Now that we have
some of the hi-res models, the 01.12Z has the snow and ice shifted
farther south with even high amounts complicating things as the
global models are not this far south. This could be convective 
related as the potential for thunder does come northward Monday 
night. The NBM probabilities for 0.25" or greater of ice are now 
in the 50 to 70 percent range from northwest Iowa into southern 
MN. The surface winds increase from the northeast Monday night 
with the approach of the deepening surface low and shift 
northwest. The winds; if they are lighter or stronger will affect 
the ice accretion as well. Some models continue to show moderate 
icing into north central WI Tuesday. With the afternoon update in 
coordination with DMX/MPX converted part of the watch to an ice 
storm warning and added Chickasaw Co. to the remained of the 
winter storm watch.

Snow: The snow/deformation band with more significant 
accumulating snow continues to set up to the west from north
central Nebraska into southwest MN and lifts through central MN 
into northern WI with the highest 24 hr probabilities of 6+ 
inches northwest of the forecast area Tuesday. Probabilities have
increased for 2 or more inches across areas along and north of
I90 Wednesday with the closed low overhead. 

Northwest winds increase on the back-side of the surface low Tuesday 
night with the snow continuing into Wednesday. Temperatures 
Wednesday will be limited due to the cold advection, thus look for
readings mainly in the 20s with a few local warm spots in the 
30s. Surface high pressure and ridging aloft will build in 
Wednesday night and Thursday with 850mb temperatures of -3 to -6. 
Cooler highs in the teens and 20s are forecast for Thursday. A 
clipper type system passes to the north and provides some 
moderation in temperatures ahead of it Friday and backdoor cooling
behind it Friday night. 

Another storm system tracking from the West Coast into the Rockies 
and Plains Saturday could bring a wintry mix next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1134 AM CST Sun Jan 1 2023

As a shortwave passes to our north, a cold front will drop
southward into the area. Behind this front ceilings will become 
IFR/MVFR. It currently looks like these clouds will move into the
area overnight.

Like this morning, it looks like some areas of dense fog will
develop overnight. The highest probabilities look to be at KRST.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Monday evening through Tuesday afternoon 
     for WIZ017-029-032>034.

MN...Ice Storm Warning from 6 PM Monday to 6 PM CST Tuesday for 
     MNZ086-094.

     Winter Storm Watch from Monday evening through Tuesday afternoon 
     for MNZ079-087-088-095-096.

IA...Ice Storm Warning from 6 PM Monday to 6 PM CST Tuesday for 
     IAZ008-018.

     Winter Storm Watch from Monday evening through Tuesday afternoon 
     for IAZ009-019.

&&

$$

DISCUSSION...Boyne/Zapotocny
AVIATION...Boyne