811
FXUS63 KGRB 301700
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1200 PM CDT Sat Aug 30 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Areas of dense fog this morning; additional fog may develop
  overnight tonight.

- Seasonably mild, dry weather is expected through early next week.

- Showers and non severe thunderstorm chances increase (50-80%
  chance) late Tuesday into Wednesday, with scattered showers
  and unseasonably cool temperatures for late week.

&&

.DISCUSSION...
Issued at 237 AM CDT Sat Aug 30 2025

Today-Monday: Dry and mild, morning fog

GOES Nighttime Microphysics Imagery show an area of stratus from
southeast Minnesota through southern Wisconsin and thickening
fog/stratus across central into northern Wisconsin. With most
surface stations showing small dew point depressions and light
winds, radiational fog will likely expand through sunrise. Based
on webcams, observations and the satellite footprint of fog,
issued a Dense Fog Advisory for central into north-central
Wisconsin and will monitor for any additional expansion through
sunrise. The fog/stratus will gradually lift through the
morning, giving way to mostly sunny skies.

Otherwise, a very pleasant Labor Day weekend is shaping up within a
split flow regime with mid-level northern stream ridging and surface
high pressure across the Great Lakes resulting in seasonably warm
temperatures and light winds. With the dry airmass in place,
overnight lows will tend to be in the 40s to low 50s with highs
mainly in the 70s to near 80 in spots.

With the persistent surface ridging and light flow through Monday,
some overnight fog development will be likely, although the
signal for tonight for dense fog is not as strong as it is
early today, areas of fog should develop after midnight.

Tuesday-Friday: Turning much cooler

A sharp change in weather pattern is expected heading through mid to
late this coming week. A strong mid-level trough will drive south
and east from the Canadian prairies into the Great Lakes Tuesday
into Wednesday with an amplified longwave trough becoming
established across the eastern US for the second half of the
week.

Shower chances increase later Tuesday into Wednesday (50-80%) as a
cold front moves through. Some thunder will be possible, but
moisture advection ahead of the system looks modest, limiting
instability. Additional shortwave troughs rotating through the
parent trough through late week will result in some continued shower
potential, but chances remain low (20-30%) given low confidence in
timing/strength of these waves.

Temperatures will trend much colder for mid to late week with
NAEFS 850 mb temps forecast below the 1st percentile compared
with climatology by early Thursday across parts of the region.
The interquartile (25-75th percentile) NBM max temperatures are
only in the 50s and 60s Wednesday-Friday with lows in the 30s
and 40s by Thursday/Friday mornings. Highs may be near record
low max values in some spots on Thursday. Combined with
breezy/gusty post-frontal northerly winds, it will certainly
feel more fall-like after the mild start to the week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1159 AM CDT Sat Aug 30 2025

Ample boundary layer moisture trapped within a surface high
continues to contribute to scattered or broken areas of fair
weather clouds from 1-3 kft. Ceilings will continue to lift and
scatter out this afternoon.

Light winds and mostly clear skies will persist into tonight as
high pressure continues to influence the regional weather. Once
again, conditions will prove favorable for areas of fog to develop
after 07-08z tonight. Though the signal in guidance is not as
strong as last night, added tempos at AUW/CWA/RHI for 1/2sm
visibilities and bkn002 ceilings. With some mixing today,
confidence is lower than the 18z forecast from yesterday.

The fog and ceilings should lift by mid-morning, which should
evolve into a broken cumulus field over north-central WI (cloud
bases 3-4 kft) but leave good flying weather for the rest of
Sunday elsewhere.

&&

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

&&

$$

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