732
FXUS63 KGRB 092354
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
554 PM CST Tue Dec 9 2025

Updated aviation portion for 00Z TAF issuance
and new information added to update section

.UPDATE...
Issued at 526 PM CST Tue Dec 9 2025

Strongly considering upgrading the advisory to a Winter Storm
Warning in parts of the Fox Valley/lakeshore areas, with the
highest likelihood in Outagamie, Winnebago, Calumet and Manitowoc
counties, where probabilistic forecasts show a 50-80% chance of
6+ inches. Also considering downgrading Lincoln County to an
advisory. Will also need to take a look at the far northern
counties, where it`s looking less likely for significant snow
accumulations. Models have largely settled on the heaviest snow
falling south of a line from Wausau to Manitowoc, with the highest
snowfall rates (1+ inch/hour) occurring from this evening into
the early overnight hours (02z-08z/Wed). Additional accumulations
occur as the deformation zone pulls through the area late tonight
into early Wednesday morning.

Will make final headline decisions within the next hour, and get
updates out before the heavier snowfall rates move into the
forecast area.

&&

.KEY MESSAGES...

- Snow will overspread the region late this afternoon/evening,
  exiting by around sunrise Wednesday. Rates may reach or exceed 1
  inch per hour across central into east-central Wisconsin this
  evening resulting in hazardous travel conditions.

- Much colder temperatures arrive for the end of the week. Bitter
  cold wind chills likely will be as low as 10 below to 30 below
  zero at times through the weekend.

- Periodic light snow chances will continue late this week into
  early next week with the highest chances on Friday (30-50%).

&&

.DISCUSSION...
Issued at 226 PM CST Tue Dec 9 2025

Tonight-Wednesday: Snow Tonight, Gusty Winds Wednesday

GOES water vapor imagery early this afternoon shows the shortwave
trough of interest across the northern plains. Snow has been
occurring across parts of Minnesota within strong mid-level warm
advection ahead of the 990 mb surface low. This snow will quickly
advance south and east this evening/overnight with the low passing
across southern Wisconsin.

Overall, high res guidance has trended a bit south, more in line
with global (GEFS/ECMWF) ensembles, with the highest precipitation
amounts forecast in a narrow stripe across central into east-central
Wisconsin just north of the strong surface low. As a result,
trimmed snow amounts across northern Wisconsin and replaced the
Winter Storm Warning with and Advisory for a few counties.
Northern areas may need to even trend lower with amounts this
evening. On the southern end, Waushara County was added to the
warning with generally medium (40 to 60%) chances for 6" from
central into east-central Wisconsin.

These systems are difficult to nail down the details for, with
higher rates associated with stronger mesoscale forcing
potentially impacting amounts. Trends across parts of the Fox
Valley and lakeshore areas will need to watched this evening as
some guidance extends an axis of localized amounts in the 6-7 inch
range towards parts of the Fox Valley. Snow rates could exceed 1
inch per hour for a 2 to 4 hour window centered on this evening
across central into east-central Wisconsin, resulting in
difficult travel. Snow should be quickly waning by sunrise on
Wednesday as the low pulls east.

Winds will pick up from the north late tonight and Wednesday as the
low pulls east with some gusts in the 20 to 30 mph range. This
likely will be insufficient to cause true blowing snow, but some
drifting may occur.

Thursday-Tuesday: Colder, Light Snow at Times

Heading through the late week period, a cold northwest flow pattern
will prevail across the Upper Midwest. A few embedded waves in the
flow will bring some potential for light snow. Right now the highest
snow chances are centered on Friday as the Arctic front slides
through with probabilities for an inch of snow in the 30 to 60%
range. However, additional shortwaves will dive southeast from
the northern plains Thurs/Thurs Night, Saturday, and possibly
early next week, so it`s an active pattern.

The most significant impact will be the push of Arctic air for the
weekend. EFI values for high/low temps drop below -0.8, indicating
strong ensemble agreement for anomalous cold over the weekend. Highs
may struggle to top the single digits over the weekend as low-level
cold advection persists with the ridge axis passing west of the
area. Cold weather headlines may be needed this weekend, although
there is uncertainty with cloud trends, which may impact temps.

By early next week, progressive ridging spreading eastward will
allow temps to rebound, but the spread increases considerably by
early next week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 526 PM CST Tue Dec 9 2025

Light snow was moving into central WI early this evening, slightly
slower than previously thought. The steady snow will overspread
all but far northern WI this evening, with moderate to heavy snow
likely along and south of a line from Wausau to Manitowoc, where
accumulations of 5 to 7 inches are expected. The heaviest snows
will occur from this evening into the early overnight hours,
though light to occasionally moderate snow will continue in
association with the system deformation zone later tonight into
early Wednesday. Flight conditions will mainly be in the IFR/LIFR
categories, but localized VLIFR vsbys could accompany any pockets
of heavy snow.

The snow tapers off late tonight into early Wednesday, but MVFR
ceilings should persist through mid to late afternoon, when at
least partial clearing is expected to arrive.

Easterly winds are expected into the early overnight, followed by
increasing north winds late tonight into Wednesday. The northerly
winds are expected to gust to 20 to 30 kts, locally to near 35
kts near Lake Michigan.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST Wednesday for WIZ005-010-
011-019>021.

Winter Weather Advisory until 9 AM CST Wednesday for WIZ013-022-
038>040-048>050-073-074.

Winter Storm Warning until 6 AM CST Wednesday for WIZ018-030-031-
035>037-045.
&&

$$

UPDATE.........Kieckbusch
DISCUSSION.....JM
AVIATION.......Kieckbusch