A surge of heat and humidity is expected to spread across parts of the Upper Midwest this week as an upper-level ridge builds over the central United States, bringing southerly flow and higher moisture into the region.
What to expect this weekend and Monday
Cloud cover has kept much of western Wisconsin cooler so far, but occasional breaks of sunshine have already allowed some locations to climb into the 80s. A warm front positioned to the south of Eau Claire has contributed to instability and showers near a boundary across northern Illinois and southern Wisconsin, with the best evening rain potential located south of I-90.
As the warm front lifts northward overnight, areas will remain mild with temperatures falling into the upper 60s to low 70s. On Monday many parts of the region are forecast to reach the 90s — potentially the first 90°F readings of the month — with humid conditions giving a tropical feel to the day.
Forecasters flag three main points for the next 24–48 hours:
- Temperatures: Most places should see upper-80s to low-90s on Monday, dependent on cloud cover.
- Humidity: Dew points will rise as southerly flow advects moisture into the area, producing uncomfortable muggy conditions and boosting perceived heat.
- Rain and storms: Although moisture is increasing, a temperature inversion aloft — known as a cap — is expected to limit widespread thunderstorm development, reducing overall rain coverage.
Heat index, health and timing
Because humidity will be elevated, the heat index — how hot it feels when humidity is considered — is likely to climb to the mid-90s during the warmest part of Monday. That raises the risk of heat-related discomfort for people outdoors, and it is sensible to take the usual precautions: stay hydrated, take breaks if working or exercising outside, and seek shade or air conditioning when possible.
Cloud cover will be the key variable that decides whether any given spot reaches 90°F. On sunnier trajectories within the warm sector the 90s are more likely, while persistent cloudiness will keep temperatures in the upper 80s.
Cold front brings relief later on Monday and into Tuesday
A cold front is expected to move through the region on Monday afternoon, switching winds to the northwest and beginning a gradual cooldown. Behind the front, dew points are forecast to fall on Tuesday even as temperatures remain seasonably warm, generally in the upper-80s.
| Timing | Key change |
|---|---|
| Late Sunday into Monday | Warm front lifts north; humid, warmer air spreads |
| Monday afternoon | Cold front passes; winds swing northwest |
| Tuesday | Drier air, lower dew points; temperatures slightly cooler |
There will still be some rain chances through the period. Showers and a few storms were noted near the boundary over parts of northern Illinois and southern Wisconsin early on, and isolated activity may persist, but the capping inversion is expected to limit the coverage of stronger storms across the region.
Practical advice for readers: if you are planning outdoor activities on Monday, monitor local forecasts for cloud trends and any midday advisories. Prepare for muggy conditions and the possibility of limited, brief downpours, but also for stretches of unbroken heat if skies clear. Workplaces and event organisers should consider water breaks and shaded rest areas for outdoor staff and participants.
In short, meteorological summer will finish this week with a warm reminder: a ridge-fuelled push of heat and humidity will lift temperatures into the upper-80s and low-90s for many, with relief arriving as a cold front moves through on Monday afternoon and ushers in slightly drier conditions by Tuesday.
