568
FXUS63 KGRB 201102
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
602 AM CDT Sun Sep 20 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Hazardous boating and swimming conditions are expected on the
  Bay and Lake at times through Tuesday.

- A quieter and drier weather pattern will settle into the region
  early to mid next week. Patchy frost will be possible at times
  across the northwoods.

&&

.DISCUSSION...
Issued at 128 AM CDT Sun Sep 20 2026

The latest RAP analysis and satellite/radar imagery show low
pressure over eastern Iowa and a warm front extending east across
central Illinois. Thunderstorm activity is occurring just north of
the warm front, while further north, weaker lift originating from
mid-level convergence is producing areas of light rain and
drizzle from central Wisconsin to Door County. Further north,
northern stream energy is pushing a cold front south across
northern Minnesota and Lake Superior. An area of clearing is
occurring between the cold front and low clouds over northeast WI
where patchy fog is occurring, dropping visibilities below 1 mile
in spots. The reductions in visibility should be relatively
brief. As the cold front drops south across the region, ceiling
trends, gusty winds, and hazardous marine conditions are the focus
of this forecast.

The cold front will continue to drop south across northern WI this
morning and central WI this afternoon. The front will bring a band
of broken cloud cover, augmented by moisture fluxes via north
winds off Lake Superior. The result will be partly to mostly
cloudy skies for much of the day. Mixing into a surge of drier air
aloft should result in partial clearing late this afternoon into
early this evening.

More low clouds are expected to develop tonight as conditions
become very unstable over northern Lake Michigan. Inversion
heights under 5 kft will limit the lake effect rain potential.
These clouds will likely stick around into Monday. A much cooler
airmass combined with cloud cover will result in temperatures
several degrees below normal today and Monday.

In a pattern which is more typical of spring, shortwave energy
originating from the western CONUS trough will slowly migrate east
from the central Plains to the southern Great Lakes to the east
coast during the upcoming work week. To the north, a Hudson Bay
high pressure system will build south into the northern Great
Lakes. The result will be a very dry and stable airmass across
the region which will shunt rain chances far south of the region.
With the dry airmass comes potential for frost across the
northwoods on Monday night and Tuesday night. High temperatures
will be undergoing a slow warming trend from the lower to middle
60s early in the work week to the low to middle 70s by Friday and
Saturday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 602 AM CDT Sun Sep 20 2026

IFR and MVFR stratus associated with a low pressure system over
Illinois is finally exiting to the southeast. Meanwhile, a cold
front is dropping south over northern WI and creating a
relatively narrow band of MVFR ceilings northwest of Rhinelander
(KRHI). In between these features, an area of clearing has
occurred, which is producing patchy IFR vsbys and LIFR or IFR
ceilings.

The band of clouds over northern WI will gradually drop southeast
today and added a tempo group to the KRHI, KAUW, and KCWA TAFs for
MVFR ceilings. Medium confidence that ceilings will be VFR by the
time they reach KGRB and KATW around 14-15Z. Ceilings will
gradually rise from late morning through the afternoon, and mostly
likely become VFR at all terminals by 17-19Z.

After a period of clearing late this afternoon into the evening,
northeast winds will bring in lake effect clouds to northeast WI
that will drop ceilings back down to MVFR.

Northeast winds will increase to 10-20 kts with gusts to 25 kts
on this morning, with locally higher gusts possible, especially
near Lake Michigan.

&&

.MARINE...
Issued at 128 AM CDT Sun Sep 20 2026

Northeast winds will increase today with passage of the cold
front. Gusts from 20 to 30 kts will be likely at times into
Tuesday thanks to a potent high pressure system keeping a tight
pressure gradient over the Great Lakes. Based on the latest data,
winds and waves should rapidly increase by 7 AM today. Therefore,
the Small Craft Advisory and Beach Hazard Statement look on track
to start this morning. An extension may be necessary on the Bay
and Lake north of Sturgeon Bay through Monday afternoon or
evening.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through Monday afternoon for WIZ022.

Beach Hazards Statement through Tuesday evening for WIZ040-050.
&&

$$

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