005
FXUS63 KGRB 271134
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
634 AM CDT Sun Sep 27 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Patchy dense fog is expected over eastern and northeast
  Wisconsin early this morning.

- Light rain showers are possible across central Wisconsin today,
  with better rain chances arriving Tuesday afternoon through
  Wednesday night.

- Trends favor a return to dry weather from Thursday through Saturday
  despite lower forecast predictability.

&&

.DISCUSSION...
Issued at 123 AM CDT Sun Sep 27 2026

High pressure is pumping in a dry airmass across the western Great
Lakes while an approaching low brings mid and high level clouds in
across the region. In areas without so many clouds, some fog is
forming, mainly across northeast Wisconsin and the lakeshore. This
fog should dissipate sometime this morning after sunrise and after
some mechanical mixing. The approaching low will bring a shortwave
some some better moisture in across western Wisconsin during the
day. While most of this precipitation will stay to the west given
the aforementioned feed of dry air from a high over eastern
Canada, some light rain or sprinkles could sneak their way in
across western portions of central and north-central Wisconsin
during the day.

Dry weather and light winds return tonight as the main energy from
the low lifts to the northeast. Models suggest fog will be a bit
more dense and ubiquitous tonight into Monday morning given
abundant low level moisture, clearing skies, and light winds. The
worst of the fog looks like it will be across north-central
Wisconsin, although it could also develop across central Wisconsin
west of Highway 39. Given current trends it would not be entirely
shocking for a Dense Fog Advisory in the future late tonight into
Monday morning, especially for north-central Wisconsin, if trends
continue.

A more widespread period of precipitation is expected from
Tuesday afternoon through Wednesday night. Models have taken a
turn this run, with the chance for half an inch or more of rain
increasing to 40 to 60% and a 20 to 40 percent chance of
receiving one inch or more of rain. This trend is due to the
slower progression of the low through the western Great Lakes,
giving the area more time to reach those rainfall amounts. We are
still only on Sunday, so further adjustments are still possible as
this system gets sampled by the RAOB network.

Dry weather trends favored Thursday through Saturday: Forecast
predictability decreases considerably from Thursday onward due to
a large spread in guidance regarding the evolution of the
southern stream system. Despite this uncertainty, current trends
support a higher potential for dry weather returning to the area
from Thursday through Saturday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 634 AM CDT Sun Sep 27 2026

Patchy fog across far northeast Wisconsin has also affected
portions of central Wisconsin and the Fox Valley with conditions
varying between VLIFR and MVFR. This fog should mix out in the
next few hours from daytime heating and mechanical mixing as a low
pressure system approaches from the west. Mid and high clouds will
continue streaming in from the west as this system approaches,
with any rain from this system expected to either remain just west
of the TAF sites, or produce a sprinkle at RHI/AUW/CWA. Either way
it won`t be impactful enough to include in the TAFs.

Light winds, some clearing skies, and low level moisture will once
again lead to fog development later tonight into Monday morning.
Models have a stronger signal for more widespread fog across
north-central Wisconsin with some also developing west of Highway
39. Given the model consensus will hit the RHI airport hardest
tonight going down to LIFR/VLIFR and bring some MVFR/IFR fog
across AUW/CWA as confidence in the dense fog is less further
south. At this time the dense fog is not anticipated across the
east-central Wisconsin TAF sites tonight with less low level
moisture trapped under the inversion.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....Kurimski
AVIATION.......Kurimski

NWS GRB Office Area Forecast Discussion