Merrill, WI 54452 Weather

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

None.