NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 121147
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
647 AM CDT Thu Mar 12 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Winter system to bring up to 5-7 inches of snowfall to northern
  Wisconsin (50-70%), with amounts rapidly tapering off southwards
  where rain may mix in.

- Strong winds accompany the system tonight through Friday, with
  periodic gusts up to 40 to 50 mph possible, which will increase
  the impacts of any falling snow and may result in rapid
  reductions in visibility at times.

- Major winter storm will be possible for the weekend with the
  potential for significant disruptions to travel across the
  region. Significant snow totals are possible, with probabilistic
  guidance painting out areas of greater than 70% chance of
  exceeding a foot of snowfall between Saturday night and Monday
  morning. Those with weekend travel plans should closely monitor
  the weather.

&&

.DISCUSSION...
Issued at 307 AM CDT Thu Mar 12 2026

Winter weather remains the focus of the forecast this week, with
another impactful winter system in the works for tonight followed
by the potential for a major winter storm over the weekend.

Today through Friday...

Relatively fast moving and tightly wound low pressure system will
move into the region this afternoon and evening, bringing
widespread precipitation the western Great Lakes. Dynamics with
this system will be impressive, between the LFQ of an upper jet,
middle level shortwave, and decent frontogenetic forcing across
the far north, resulting in periods of 1"/hour snowfall rates at
times during the overnight period. The highest snowfall will be
across north-central into northeastern Wisconsin, where forcing
better aligns with the DGZ on the model soundings. Timing-wise,
the majority of the snow will be in the early to middle of the
night period, with lesser amounts of snow on the back end of the
system as colder air arrives through Friday morning.
Probabilistic guidance also paints this area out for around
50-70% chance of exceeding 6 inches. Further south, the nearby
proximity of the surface warm front will allow rain to mix in,
resulting in a sharp gradient in snowfall totals as you head
southwards towards a line between Wausau and Oconto. The strong
dynamics present in the system will also result in very strong low
level winds, with 45 knots at 925mb and 55 knots at 850mb. With
the heavy precipitation rates expected in this system, would
expect periodic mixing of winds to start overnight as
precipitation increases, with some wind concerns lingering on into
Friday. As a result of all this, have brought in Winter Storm
Warnings across northern Wisconsin where the combination of high
snowfall rates and wind will have the greatest impacts to travel
and possible power infrastructure. Further south Winter Weather
Advisories are in effect for the areas most likely to see some
rain mix in at times across portions of central to east-central
Wisconsin and finally a Wind Advisory is in effect for the rest of
the area where relatively minimal snowfall is expected but
periodic wind gusts remain likely through Friday afternoon.

Weekend System...

A strong Colorado low will lift into the Northern Plains Saturday,
bringing widespread precipitation into the western Great Lakes.
Strong dynamics will promote heavy precipitation and another
period of strong winds, marking the potential for a significant
winter storm Saturday night into Monday morning. QPF remains
impressive with this system, with models consistently producing
2-3 inches of liquid across portions of Wisconsin. Converted to
snow, some impressive snowfall totals seem likely. As of the
current forecast cycle, probabilistic guidance shows a wide region
of greater than 70% chance of exceeding a foot of snowfall across
much of central to east-central Wisconsin. Couple this with the
around 80-85% chance of exceeding 30 mph wind gusts, and
significant winter impacts become likely. This is corroborated by
the Winter Storm Severity Index, which brings a 60-70% chance of
major impacts into the Fox Valley. All this said, the uncertainty
in the forecast for the snowfall specifically will be on the
southern edge of the precipitation, where some models now produce
a sufficient warm layer to mix in both ice pellets and freezing
rain. This will be a major factor to watch in subsequent forecast
both for modifications to the overall snowfall totals but also the
impacts any freezing precipitation would have in its own right.
Suffice to say, Sunday will be a day to closely monitor the
forecast if you have any travel plans in the area.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 647 AM CDT Thu Mar 12 2026

Good flying conditions are expected last for the morning and early
afternoon before conditions quickly deteriorate in the late
afternoon into the evening. A strong clipper system will bring
snow to much of the region, dropping both ceilings and visibility
during the evening and overnight hours across much of the area.
Expect IFR to LIFR conditions during this overnight period. Some
rain may mix in at times on the southern edge, so was a little
more optimistic about visibility for GRB, ATW, and MTW near the
Fox Valley, but would overall still expect IFR conditions. Snow
rates will be fairly high across the north, which may impact
ground operations for terminals in this area such as RHI.

Strong winds will accompany this system, with gusts up to 30 to 35
knots expected to reach the surface at times overnight. Winds
aloft will be even stronger therefore included periods of wind
shear despite the expected mixing towards the surface. Winds will
likely stay strong well into Friday but snow is expected to
subside by the mid to late morning hours.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 7 PM this evening to 1 PM CDT Friday
for WIZ005-010>013-018>021-073.

Winter Weather Advisory from 10 PM this evening to 1 PM CDT
Friday for WIZ022-074.

Winter Weather Advisory from 7 PM this evening to 1 PM CDT
Friday for WIZ030-031.

Wind Advisory from midnight tonight to 6 PM CDT Saturday for
WIZ035>040-045-048>050.
&&

$$

DISCUSSION.....Uhlmann
AVIATION.......Uhlmann