Severe weather is also possible in the Midwest.

At least 21 states have some type of heat alert Saturday, from the Great Plains to New England.

Heat index values are expected to soar into the triple digits for the central U.S. Saturday, while heat index values in the 90s will impact the Northeast.

The heat wave will continue to build through the weekend, especially in the Northeast, where cities are expected to remain in a heat wave through the beginning of next week. Heat index values will hover in the triple digits from Washington D.C. to Philadelphia and even New York City through at least Tuesday.

Heat isn’t the only weather-related issue impacting the U.S. this weekend. More than 11 million people are at risk for severe weather Saturday across the Midwest and western Great Lakes region.

The main threats will be potentially damaging wind and large hail and a few possible tornadoes.

Meanwhile out west, red flag warnings remain in effect through Saturday night for portions of Idaho and Wyoming. Dry air, along with wind gusts near 30 mph, pose a risk for fires to easily spread Saturday.

Conditions are expected to improve later this weekend.