355
FXUS63 KGRB 050342
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1042 PM CDT Thu Sep 4 2025

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 754 PM CDT Thu Sep 4 2025

A strong low pressure system is approaching Minneapolis early this
evening. Strong frontogenesis on the nose of a 40 kt low level jet
is leading to a band of rain on the northern flank of this surface
low. Convection developed a short time ago along the cold front
over southern Minnesota which prompted a tornado warning, but no
lightning is currently being detected. Winds are gusting 35 to 40
kts behind the surface low.

This low remains on track to move northeast from west-central WI
to far northeast WI through the night. Can`t rule out a
thunderstorm (likely on the leading edge of the dry slot) given
the very impressive dynamics, but there is no instability leading
to a low probability of any thunder (under 10%). The low will
bring a period of light to moderate rain to the region tonight,
which has already started over north-central WI.

Although not as large as 24 hours ago, models continue to show a
large range of wind gusts possible after midnight. But dynamics
are awfully impressive, so continued to error on the higher side
of guidance, which brings 30-40 mph gusts from central to
northeast WI from about 2 am to 9 am Friday. Gales on the Lake and
Bay remain possible, but just shortened the window slightly
(chances peak about 3 to 6 am).

All this said, changes to the current forecast were relatively
minor.

&&

.KEY MESSAGES...

- Widespread rainfall will impact the region tonight (90% to 100%
chance).

- Winds will gust from 25 mph to near 40 mph tonight, especially
across along the lakeshore.

- Gale force winds and high waves are expected late tonight into
  Friday morning on the Bay and on the nearshore waters of Lake
  Michigan.

- Near-record cold maximum temperatures are possible through
this weekend.

&&

.DISCUSSION...
Issued at 350 PM CDT Thu Sep 4 2025

Precipitation Chances...

Precipitation chances for this evening and overnight near 90 to 100
percent across our entire forecast area, as an area of low pressure
will swing from west to east across the northern portion of
Wisconsin. With this low pressure area centered to our north, the
rainfall amounts will increase the further north one travels in
Wisconsin. As of Thursday afternoon, rainfall totals of 0.50 to 1.00
inch are anticipated mainly north of Highway 29, with lesser amounts
south of Highway 29. There is roughly a 25 percent chance of
rainfall totals exceeding 1 inch along the WI/MI border. Timing-
wise, confidence is high that the rain will arrive in central
Wisconsin around 6 pm or so, and make it to the Fox Valley region
around 10 pm or so.

Hi-res models have the brunt of the rainfall moving east of our area
between 4am and 7am Friday at the latest. The one exception is along
the Wisconsin/Michigan border, where light showers/sprinkles are
expected to linger on/off throughout most of Friday afternoon.
Rainfall accumulations after 7 am Friday in far northern Wisconsin
will be minimal-only a few hundredths at best.

Surface high pressure looks to build over the area into Sunday,
putting an end to the showers and bringing sunshine back into the
area. For the next widespread rain chances, there is widespread 20%
to 40% chance of light rain towards next week Tuesday-
Wednesday.

Elevated Wind Speeds Tonight...

Accompanying the quick-moving low pressure system for tonight into
Friday will be followed by strong (35-45 kts) westerly low-level
winds and strong CAA. This will allow for surface winds to quickly
increase late tonight with gusts of 25 to 40 mph expected--highest
gusts across the Fox Valley region and the lakeshore. The strongest
winds are expected from 4 am to 7 am tonight. For tomorrow
afternoon, winds will likely remain in the 20 to 30 mph range. Wind
direction will be mainly from the west... meaning there may be very
minor travel impacts to vehicles (especially high-profile ones)
traveling on north-south routes.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1042 PM CDT Thu Sep 4 2025

A potent low pressure system will be moving across northern
Wisconsin overnight, bringing periods of rain, wind, and poor
flight conditions.

Light to moderate rain will continue to move across the region
over the next several hours. Moderate rain is expected until about
08z across far northern WI, which will drop visibilities to MVFR
and lower ceilings to IFR/MVFR.

Visibilities will improve once this period of moderate rain ends,
but ceilings will likely struggle to rebound over central and
north-central WI (AUW/CWA/RHI) late tonight and Friday. RHI may
remain MVFR for much of the day in occasional light showers.
GRB/ATW/MTW will likely see a a period of MVFR ceilings only to return
to VFR conditions by early afternoon Friday.

On the backside of the low, gusty winds are expected, strongest
over central to east-central WI (30-35 kts) late tonight into
early Friday morning. Then west winds will remain gusty to 25 kts
for much of Friday. Winds will gradually diminish on Friday
evening.

A period of low level wind shear will diminish late overnight.

&&

.MARINE...
Issued at 350 PM CDT Thu Sep 4 2025

Waves and southerly winds will rapidly increase late this evening
and tonight due to the passage of the surface low pressure system.
By Friday morning, winds will turn westerly, but will remain gusty.
There is a strong enough signal for a brief period of gales (35-40
kts) to occur on the Bay of Green Bay and the nearshore waters along
Lake Michigan from late tonight through mid-Friday morning to
warrant the issuance of a Gale Warning (1 AM to 10 AM Friday).
Dangerous swimming conditions are likely to occur along Lake
Michigan beaches late tonight into Friday morning as well. A
Small Craft Advisory will likely be needed following the Gale
Warning as gusty westerly winds will continue through Friday
evening.

&&

.CLIMATE...
Issued at 350 PM CDT Thu Sep 4 2025

The unseasonably cold airmass will bring the chance of setting
record low maximum temperatures Friday (9/5), and Saturday (9/6).
Here is a look the current records and forecast values for Green
Bay, Rhinelander, and Wausau.

 Green Bay

Date           Record Low Max       Forecast High
----           --------------       -------------

9/5              60F(1981)               57F
9/6              58F(1965)               61F

 Rhinelander

Date           Record Low Max       Forecast High
----           --------------       -------------

9/5              55F(2017)               50F
9/6              55F(1956)               56F

 Wausau

Date           Record Low Max       Forecast High
----           --------------       -------------

9/5              57F(1956)               54F
9/6              56F(1965)               59F.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 10 AM CDT Friday for WIZ022-040-
050.
&&

$$

UPDATE.........MPC
DISCUSSION.....Kotenberg
AVIATION.......MPC
MARINE.........Kotenberg
CLIMATE........Kotenberg