Smoke from Canadian wildfires again blanketed parts of Wisconsin on Monday, leading to familiar hazy skies.

Air quality was worst Monday in Dane, Eau Claire, Grant, Jackson, Monroe and Sauk counties, where the AQI, or air quality index, is unhealthy for sensitive groups.

Air quality should improve later in the week, but extreme heat was to make its way into the region as well.

Hot and humid weather is expected to begin Wednesday, with much of the Midwest under an extreme heat watch. The National Weather Service is predicting dangerously hot conditions across most of Wisconsin, with heat indices of at least 100 degrees in Milwaukee and Madison. Heat index measures how hot it feels when humidity is combined with air temperature.

Western parts of the state, including La Crosse and Prairie du Chien, could also reach “feels like” temperatures exceeding 100 degrees.

The Iron Mountain area was expected to have temperatures close to 90 on Wednesday, according to the NWS office in Marquette.

Experts recommend staying hydrated, remaining in air-conditioned spaces and keeping out of the sun. Checking in on relatives and neighbors, especially older people, is important, as is ensuring kids and pets are not left unattended in cars. On the hottest, most humid days, the NWS predicts cars could reach lethal temperatures in a matter of minutes.

The heat should peak Wednesday, with chances of showers and thunderstorms in the region Thursday into Friday.