Extreme heat, flash flooding, and severe thunderstorms are forecast for tens of millions of people across the country this weekend.

Even though June 21 marks the first day of summer, temperatures across the country already feel like the peak of the season.

An estimated 26 million people will experience extreme heat across the West, the Plains and the Southeast. Some areas — including Raleigh and Wilmington, North Carolina; Myrtle Beach, South Carolina; Tallahassee, Florida; Hattiesburg, Mississippi; and Tulsa, Oklahoma — could see temperatures reach as high as 108 degrees, with most daytime highs settling in the 90s. These readings are roughly 5 to 10 degrees above typical mid-June levels.

The West Coast is also bracing for rising temperatures, with highs climbing to 10 to 25 degrees above normal this weekend. Daytime temperatures will range from the 80s to over 100 across California, Oregon and Washington, with active heat alerts in effect for Bakersfield and Redding, California; Portland, Oregon; and Seattle.

Heat isn’t the only threat. Severe thunderstorm watches are in effect through 3 p.m. CT Saturday for portions of Nebraska, Iowa and Missouri. An additional 20 million people face the risk of strong to severe storms this weekend, with activity expected to develop after 6–7 p.m. across Kansas, northeast Oklahoma, Missouri and northwest Arkansas.

Flash flood alerts are also in place for those areas. Cities most at risk include Kansas City; Tulsa; Wichita, Kansas; and Springfield and Joplin, Missouri. Additional hazards include possible tornadoes, wind gusts up to 75 mph and large hail, with storms likely to persist through the evening.

By Sunday, showers and thunderstorms are expected to push into parts of the mid-Atlantic, Appalachians and Ohio Valley, putting as many as 54 million people at risk — including those in New York City, Philadelphia, Baltimore and Washington. Storms in those areas could produce wind gusts exceeding 65 mph and quarter-sized hail through the afternoon and evening.

The weekend’s severe weather follows a turbulent stretch earlier this week, when severe weather placed 13 million people under flood watches and triggered widespread power outages. At one point Tuesday afternoon, 35,000 customers across Kansas were without power.

Some of these temperature shifts could be linked to El Niño, a natural climate pattern that warms surface temperatures in the tropical Pacific. Its effects can amplify the warming already driven by climate change.