Waupun, WI Weather

Key Messages

- Areas of fog look possible tonight, mainly over east central and southeast Wisconsin. This fog may become dense in time for the morning commute.

- Dry with a gradual warming trend through next weekend.

Update

Issued 709 PM CDT Mon Oct 19 2026

Short range guidance continues to hone in on the potential for fog overnight, mainly east of where a lake breeze pushed inland this past afternoon. Looking at radar observations, the lake breeze boundary pushed inland to roughly a line extending from the western border of Fond du Lac County, south through Beaver Dam, and southward through Elkhorn in Walworth County.

Provided high clouds clear in a timely manner tonight, the subsidence overhead, coupled with light winds and the lake modified air at the surface, should allow for areas of fog to form east of said lake breeze boundary. Guidance shows the potential for this fog to become dense in spots just in time for the morning commute. The fog may then linger until 9 or 10am given the lower sun angle and weaker mixing this time of the year. Visibility trends will be monitored for either an SPS or a Dense Fog Advisory during the early morning hours. Cautious travel is advised in any fog that develops.

CMiller

Short Term

Issued 142 PM CDT Mon Oct 19 2026

Tonight and Tuesday:

The dry and quiet weather continues across southern Wisconsin with pleasant, if slightly warmer than normal, temperatures through the week. High pressure from the Northern Plains will settle in across the Great Lakes Region today and remain for much of the work week. The ridging aloft and sfc high pressure across the Central and Eastern CONUS will keep winds light (direction variable at times) and skies mostly clear. During the overnight hours, the clear skies, light and variable winds and falling temperatures will proved a good environment for some fog development. Low lying areas, fields, marshes, river valleys etc will be the most susceptible for any fog development. Fog should be patchy with limited impacts expected. Any fog that does develop will diminish shortly after sunrise. Expect nearly identical conditions to today and tonight for Tuesday and Tuesday night.

Patterson

Long Term

Issued 142 PM CDT Mon Oct 19 2026

Tuesday night through Monday:

The ridging aloft will remain in place across the central and eastern CONUS through the rest of the work week keeping conditions dry. An overall benign and quiet forecast period. The next chances, while uncertain and weak, for rain is Saturday evening/Saturday night. The ridging aloft will start to tilt and break down a bit over the weekend as a low pressure system over the Pacific Northwest starts to move east. The split among guidance is still fairly significant which you can see in the deterministic runs of the global models well. This does continue through the ensembles and the cluster analysis which continues to show uncertainty in timing, location and strength of the low. The GFS has the stronger and more progressive low, which the EURO and CAN keep the low a bit weaker and have it as a ridge rider. The track of this low will determine what comes next for southern Wisconsin. Does the flow become a bit more meridional or does it stay zonal, either way there does seem to be a slight shift int he pattern after this Saturday. This could bring some more chances for rain back into the forecast as we look into next week.

TLDR for Saturday at the sfc is the location of the low and how strong the associated cold front is uncertain. Available moisture looks to be fairly low at this point which means this could be a dry frontal passage if there isn't any good WAA out ahead of the front. There is still too many uncertainties to draw any concrete conclusions so kept to the average among guidance (5-15% POPs with better chances as you go north into central and northern Wisconsin). The slightly warmer than normal temperatures are expected to continue throughout the extended with the prolonged southerly winds.

Patterson