Marshfield, WI 54404 Weather

Update

Issued at 945 PM CDT Tue Oct 20 2026

Fog trends are the main focus for rest of tonight into early Wednesday, especially after what happened late last night into Tuesday morning.

Satellite and surface obs already pointing to patchy fog near the lakeshore. Available web cams suggest that fog so far is more shallow ground type. As cooling continues though, expect fog to expand overnight. Unlike last night, flow just off surface is turning southwest, instead of east-northeast off the bay and lake. This could be one reason why high res guidance is not as pessimistic with widespread lower visibility. Even so, think a Dense Fog Advisory may be needed for some areas later tonight, but not enough confidence at this point to issue it ahead of time. Greatest probabilities of most dense fog would be near the lakeshore and inland from the Fox Valley into far northeast WI.

Key Messages

- Patchy dense fog will develop late tonight into Wednesday morning across east-central Wisconsin and areas west of Green Bay, locally dropping visibilities below 1/2 mile.

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

- A 20 to 30 percent chance of light rain showers Saturday night into Sunday across central and northern Wisconsin.

- Cooler air filters for early next week, dropping daytime high temperatures into the 50s on Monday and Tuesday.

Discussion

Issued at 1147 AM CDT Tue Oct 20 2026

Current surface analysis shows strong high pressure centered over northern Ontario and Quebec, maintaining large-scale subsidence and light winds across northern Wisconsin. Upper-air analysis displays broad mid-level ridging over the central United States flanked by troughs over the western and eastern CONUS. Morning fog and low stratus have been slow to erode across portions of northeast Wisconsin, but further daytime heating will support clearing through early this afternoon. High pressure will linger through Wednesday before a weak, moisture- starved cold front crosses the region late Wednesday into Wednesday night.

Patchy Dense Fog Tonight And Wednesday Morning: Clear skies and light winds will create good radiational cooling conditions late tonight into Wednesday morning across east-central Wisconsin and areas west of Green Bay. Boundary layer relative humidity will approach saturation after 10 PM this evening, promoting fog development that will persist through mid- Wed morning. High confidence exists in fog dissipation by 10-11 AM Wednesday as diurnal solar heating drives boundary layer mixing.

Prolonged Mild and Dry Late Week Pattern: Persistent atmospheric ridging and deep-layer subsidence will lock in tranquil weather across north- central and northeast Wisconsin through Saturday afternoon. Daily high temperatures inland will warm into the upper 60s and lower 70s, while onshore lake breezes hold shoreline communities in the lower 60s. NBM temperature percentiles show exceptionally tight 10th to 90th percentile spreads of 2 to 4 degrees F, reflecting high forecast confidence.

Weak Weekend Front Rain Probabilities: A weak shortwave trough moving across southern Canada will push a trailing cold front into the Upper Mississippi Valley Saturday night into Sunday. Weak dynamic forcing and limited moisture transport ahead of the boundary will restrict precipitation coverage, yielding low-end 20 to 30 percent rain chances across central and northern Wisconsin. NBM probabilistic guidance shows 90th percentile 24-hour liquid accumulations remaining under 0.25 inches across the forecast area so not expecting a potential soaker. The chance of showers will taper off Sunday afternoon with partly sunny skies returning by Sunday evening.

Early Next Week Cooling Trend: Post-frontal cold advection will usher in a cooler and more seasonable airmass for Monday and Tuesday as surface high pressure builds south from Manitoba. Daytime high temperatures will fall into the lower to mid-50s across north-central Wisconsin and upper 50s across the Fox Valley. Clear skies and light winds beneath the building high will promote radiational cooling at night, dropping low temperatures into the low to mid-30s.

Aviation

for 00Z TAF Issuance Issued at 625 PM CDT Tue Oct 20 2026

Another round of fog is expected late this evening through mid- Wednesday morning. Confidence is highest for impacts over east- central WI (KMTW, KGRB, KATW), remaining lower farther west. LIFR to VLIFR will be possible between 08-13z Wed. Indications still present that ground fog will develop as early as 02-03z at KMTW.

Besides the fog, after mostly clear skies tonight, scattered mid and high clouds will pass across the region on Wednesday. Winds will be light at less than 10 kts through the period.