792
FXUS63 KGRB 211707
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1207 PM CDT Wed Oct 21 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Patchy dense fog will redevelop late tonight into early Thursday
  morning, locally dropping visibilities below 1/2 mile. More fog
  possible early Friday.

- Dry and mild through Saturday afternoon with inland high
  temperatures warming into the middle 60s to lower 70s.

- A 20 to 40 percent chance of light rain showers from Saturday
  night through Monday.

- Cooler early next week, with highs mainly in the 50s.

&&

.DISCUSSION...
Issued at 1207 PM CDT Wed Oct 21 2026

The current surface analysis shows high pressure centered from
the eastern Great Lakes into eastern Canada, while a weak cold
front moves across northeast Minnesota. Mid-level cloudiness above
10,000 feet is drifting across northern Wisconsin ahead of an
associated shortwave trough. As the cold front settles over the
region tonight, upper-level dynamics will outrun the surface
boundary, causing the front to lose definition over the state.
Persistent ridging aloft and light boundary layer winds will
maintain generally quiet weather across north-central and
northeast Wisconsin through the end of the week.

Patchy Dense Fog Late Tonight Into Thursday: As the remnant cold
front stalls over Wisconsin tonight, light boundary layer winds
and clear to partly cloudy skies will foster favorable radiational
cooling conditions. Boundary layer moisture saturation between
2 and 9 AM Thursday will promote patchy dense fog development,
particularly across far northeast WI west of the Bay. Rapid fog
dissipation expected by 9 to 10 AM Thursday as morning solar
heating drives boundary layer mixing. Conditions will remain
favorable for early morning ground fog on Friday as well.

Unseasonably Warm And Dry Through Saturday Afternoon: Deep-layer
atmospheric subsidence associated with the expansive mid-level
ridge will lock in tranquil and dry weather across the forecast
area through Saturday afternoon. Inland maximum temperatures will
warm into the upper 60s to lower 70s, while onshore lake breezes
hold shoreline communities along Lake Michigan in the upper 50s to lower
60s. NBM ensemble guidance exhibits high confidence with tight
10th to 90th percentile temperature spreads of only 2 to 4 degrees
F for daily highs through Saturday.

Increased Rain Chances Saturday Night Through Monday: A northern
stream shortwave trough advancing across central Canada will push
an associated cold front into the Upper Midwest Saturday night
into Sunday. Isentropic ascent and moisture return along the slow-
moving frontal boundary will elevate rain shower chances to 20 to
40 percent across north-central and northeast Wisconsin from
Saturday night through Monday. Rainfall probabilities and NBM
90th percentile liquid accumulations over this time period have
increased over the past 24 hours and think rain chances will
increase in subsequent forecasts.

Sharply Cooler Temperatures Early Next Week: Post-frontal cold air
advection will usher in a significantly cooler Canadian airmass
Monday night through Tuesday, dropping daytime high temperatures
into the upper 40s to lower 50s area-wide. High pressure shifting
south toward the region will maintain quiet but crisp fall
weather through the middle of next week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1207 PM CDT Wed Oct 21 2026

A cold front over northeast Minnesota will sag into northern
Wisconsin tonight and weaken in the process. A period of broken
ceilings above 9 kft will accompany the front through 21-23Z which
may produce a sprinkle near the Upper Peninsula border through
early afternoon.

Clear skies are forecast tonight. Guidance is highlighting greater
fog potential tonight in part due to lighter boundary layer winds.
Will continue to carry tempo groups for LIFR/IFR visibilities late
tonight into Thu morning. The ground fog should lift by 9-10 AM
Thu.

Winds will be light at less than 10 kts through the period.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion