A strong ridge of high pressure centered over Wisconsin will drive a multi-day heat event across the region, producing hot, humid conditions through Friday and the highest heat-index values of the stretch on Tuesday, when readings are expected to climb above 100°F.
What to expect
Sun and very warm air will dominate today and tonight, with peak heat-index values near 100°F. Overnight lows will be uncomfortably warm, dipping only into the lower 70s, keeping humidity elevated through the night. Tuesday is forecast to be the hottest day of the period as temperatures and humidity combine for heat-index values exceeding 100°F. Even locations adjacent to large lakes may see limited cooling because of an offshore west wind.
| Day | Temperatures | Heat index |
|---|---|---|
| Today | Upper 90s (air) | Near 100°F |
| Tuesday | Upper half of the 90s | Above 100°F |
| Wednesday–Thursday | Lower 90s | Hot and humid |
| Friday | Lower 90s | Scattered storms possible |
| Saturday | Lower 80s | Humidity drops — relief |
Timing and evolution
Hot and humid conditions will persist through Friday. A front moving in from the north late in the week could trigger scattered thunderstorms Friday, but substantial relief is not expected until Saturday, when cooler and drier air will lower highs into the lower 80s and reduce humidity. Sunday may trend more humid again with additional scattered storms possible.
Safety guidance
Health risks increase when heat-index values reach and exceed 100°F. Officials advise limiting outdoor exertion during peak heating hours — generally between 2 p.m. and 6 p.m. — and taking these precautions:
- Stay hydrated; drink plenty of water throughout the day.
- Check on vulnerable friends, relatives and neighbors, especially older adults.
- Never leave children or pets unattended in vehicles.
- Wear light-colored, loose-fitting clothing and use sunscreen.
- Take breaks in air-conditioned locations when possible.
First Alert updates will follow as the heat wave develops. Scattered storms late in the week may offer temporary relief in some areas, but the more widespread cool-down is expected on Saturday.
