431
FXUS63 KGRB 291101
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
501 AM CST Sat Nov 29 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Heavy snow is expected across central and northeast Wisconsin
  later today and tonight, where 6 to 11 inches of accumulation
  is forecast. Locally higher amounts exceeding 12 inches are
  possible near Lake Michigan, particularly over Kewaunee and
  Manitowoc counties.

- Hazardous travel conditions will likely persist into Sunday.
  While the snow will end Sunday morning, northwest winds gusting
  to 25 to 35 mph will cause blowing and drifting snow,
  especially in open areas and on east-west oriented roads.

- Much colder air will arrive for the start of next week. Wind
  chills may fall to 10 below zero or colder Monday morning.

&&

.DISCUSSION...
Issued at 235 AM CST Sat Nov 29 2025

The latest RAP analysis and satellite imagery show shortwave energy
digging southeast across the central Rockies early this morning, while
flow aloft remains relatively flat across the Midwest. Surface low
pressure is currently centered over southeast Colorado. Ahead of this
low, broad warm and moist advection is occurring in the 850-700mb
layer, supported by a 40 kt low-level jet nosing into Iowa.
Saturated conditions in the 900-800mb layer are occurring as close
as northeast Iowa and southern Minnesota where snow is occurring.
As the shortwave energy moves from the Rockies across the Plains
today, the surface low is progged to track from central Kansas to
the Iowa/Missouri/Illinois border by early evening, eventually
reaching the central Lower Peninsula of Michigan by 6 am Sunday.
This track will bring the Colorado Low northeast across the region
over the next 24 to 36 hours.

Short Term (Today through Sunday):

Winter Storm:  Focus of the forecast revolves around snow
accumulations and impacts as the low pressure system traverses the
region. Ascent will increase today via warm advection driven by a
40-50 kt low- level jet moving into northern Illinois, coupled
with upper divergence in the right rear quadrant of a jet streak.
Light snow will gradually spread from southwest to northeast
across the region this morning through mid-afternoon. High-
resolution CAMs indicate a mid-lake band becoming organized later
this morning and moving onshore into the northeast WI shoreline by
early afternoon. Precipitation intensity is expected to increase
significantly across the region this afternoon and evening. It is
noted that snow ratios were lowered for this forecast as the NBM
tends to have a high bias in warm advection regimes. While QPF has
trended steady, values were adjusted lower compared to the NBM,
which was running at the 75th percentile of guidance.

The heaviest snowfall is expected to target east-central Wisconsin
from late this afternoon through this evening. This intensification is
attributed to multi-bands of lake enhancement interacting with a
focused band of frontogenesis that several models develop from
Waushara to Manitowoc counties. Delta-Ts upwards of 15-17C and a
deep dendritic snow growth zone (100-150mb deep) should lead to
efficient snowfall production. Consequently, locally higher
amounts are possible near Lake Michigan, particularly over
Kewaunee and Manitowoc counties where totals may exceed 12 inches.
Some amounts could also approach 12 inches from Waushara to
Calumet counties as well if a mesoscale snowband becomes focused.
The heaviest snow will depart after midnight, with snow ending
for most areas Sunday morning. However, lake effect snow will
likely continue in the snow belt of Vilas County, where snowfall
estimates have increased to the 2-4 inch range. As a result, the
Winter Weather Advisory has been expanded into Vilas County.
Regarding timing of headlines, the start time of the advisory has
been delayed until noon, and the warning until 10 am, as impacts
from snowfall looks minimal prior to those times.

Sunday Impacts and Winds:  While the accumulating snow will
diminish Sunday morning, travel impacts will likely continue.
Northwest winds are forecast to increase just as the synoptic snow
departs, with gusts of 30 to 35 mph possible. These gusts will be
strongest where the heaviest snow is expected to fall,
specifically from the southern Fox Valley to the Lakeshore.
Blowing and drifting snow is likely, particularly on east- west
oriented roads. A Winter Weather Advisory may be needed on Sunday
as the snow diminishes and blowing snow hazards increase; however,
there is currently no need to extend the Winter Storm Warning as
little to no additional snow accumulation is expected Sunday
morning. Highs on Sunday will range from the lower 20s to lower
30s.

Long Term (Sunday Night through next Friday):

A winter-like pattern is shaping up across North America for the next
week, characterized by 5-day means showing ridging off the west coast
and troughing extending from Hudson Bay to the Great Lakes. 850mb
temperatures indicate below-normal readings, setting the stage for the
coldest air of the season thus far. Sunday night into Monday will see
wind chills falling to around 10 below zero, with highs on Monday
in the teens. Looking ahead, the system previously monitored for
Monday night continues to trend northward, though snow chances
continue to slowly rise to above 30 percent, highest over east-
central Wisconsin. By Wednesday, an arctic front will produce the
next widespread chance for snow (40 percent). Amounts with this
mid- week system look relatively light, generally an inch or two.
Arctic high pressure is then expected to build in for late in the
week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 501 AM CST Sat Nov 29 2025

MVFR to VFR conditions with overcast ceilings around 2500 to 4000
ft are expected to persist through mid-morning. However, flight
conditions will deteriorate from southwest to northeast late this
morning through early afternoon (16Z-21Z) as a robust winter storm
system moves into the region.

Snow will overspread the terminals by early afternoon, quickly
dropping conditions to widespread IFR and LIFR. The period of
highest impact appears to be late this afternoon through the
evening (22Z-06Z). During this time, heavier bands of snow will
impact east-central WI (GRB/ATW/MTW) and central WI (AUW/CWA),
resulting in ceilings falling to between 600 and 900 ft and
visibilities frequently dropping to 1/2SM to 3/4SM.

Surface winds will back from the east to the northwest late
tonight.

Outlook: The snow will diminish on Sunday morning. But northwest
winds will increase, with gusts to 20-30 kts causing blowing and
drifting snow.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon today to 6 AM CST Sunday for
WIZ005-010>013-018-019-021.

Winter Storm Warning from 10 AM this morning to 6 AM CST Sunday
for WIZ020-022-030-031-035>040-045-048>050-073-074.
&&

$$

DISCUSSION.....MPC
AVIATION.......MPC