Oconomowoc, WI 53066 Weather

Key Messages

- Patchy fog will continue across eastern WI early this morning, with a few locally dense patches possible. Patchy fog may redevelop across all of southern Wisconsin tonight into early Thursday morning.

- Dry with a gradual warming trend into Saturday night/Sunday, then possibly some showers and cooler temperatures Sunday night into early next week.

Short Term

Issued 100 AM CDT Wed Oct 21 2026

Today and Tonight:

Twin high pressure systems remain dominant across the midwest CONUS today and tonight, yielding dry and pleasant weather for southern WI. Highs around 70 degrees and lows in the mid 40s to around 50.

Main story today is some patchy fog that has developed across eastern WI, which will linger through early this morning and burn off a few hours after sunrise. The satellite signature for these patches of fog currently spans from a Burlington to West Bend to Sheboygan line east to the shoreline; this is where we could (potentially) see some locally dense patches of fog lingering into the AM commute. That said, as of right now (1:00 AM), DOT cameras reveal that the fog is 'patchy at best', barely obstructing visibility from most camera angles. We will continue to monitor, and issue an Special Weather Statement (or localized Dense Fog Advisory) if trends warrant. Janesville airport has reported some patchy fog as well, but any fog west of the aforementioned line is likely hyper-localized to river valleys and low-lying marshy areas.

Similarly, late tonight into early Thursday morning, we could see some patchy fog develop and become locally dense. This time, it could develop across all of southern WI.

Sheppard

Long Term

Issued 100 AM CDT Wed Oct 21 2026

Thursday through Tuesday:

A second high pressure system tracks southeastward across the Great Lakes region Thursday into Friday, allowing calm and mild weather to persist through the end of the work week. Nocturnal cooling could lead to additional periods of ground fog in the early morning hours of Thursday and Friday, with mostly clear skies and calm winds forecast. A weak easterly lake breeze is possible Thursday, with a synoptic (area-wide) 10 mph southeasterly breeze developing through the day Friday. As such, we expect inland highs around 70 degrees Thursday and Friday, with highs in the mid 60s for the east edge of the state. Dry weather and similar temperatures continue into the daytime hours of Saturday, with a south breeze as the high pressure system departs eastward.

Models show fair agreement on a trough / upper low tracking east across Canada this weekend, pushing out the persistent upper-level ridging across the midwest and yielding more zonal flow. Surface low pressure over the northern Great Plains on Friday lifts northward to merge with this feature into the weekend, tracking east across Ontario Canada and eventually dragging a SW to NE oriented cold front across WI. We expect this cold front to reach WI late Saturday night into Sunday (5-15% precip chances), where it could either stall over central portions of the state or cross our region and stall just south of the state border. Some more substantial precip chances (20-40%) would then arrive Sunday night through Tuesday as a separate 500mb trough phases with the stalled frontal boundary and provides some ascent. High pressure then tracks southeastward from Canada, crossing the Dakotas Monday night into Tuesday before turning east into our region. This would slowly force the frontal zone away and lower precip chances, but also deliver some cooler air early to mid next week. Models vary substantially on how cool things could get, but for now we're sticking with the middle ground of highs in the 50s and lows in the 30s/40s.

Sheppard

Aviation

Issued 100 AM CDT Wed Oct 21 2026

Patchy fog has developed around eastern WI terminals, and will linger until ~2 hours after sunrise this morning. A few locally dense patches with visibility 1/4 SM have been observed, and coverage of the fog may increase slightly until the sun begins to rise, but for now it's not particularly widespread / not worthy of an Advisory yet.

Otherwise, VFR and very light winds expected through the TAF period and beyond. Mostly clear skies. Patchy fog may redevelop tonight into early Thursday morning, this time across all of southern WI.

Sheppard