Extreme heat is impacting states across the country. See maps of high temperature forecasts and heat index levels.

Philadelphia is under an extreme heat warning with heat index values up to 105 degrees, advising residents to stay cool and hydrated.

Tens of millions sweltered across the U.S. Northeast and Midwest on Monday (June 23) as record-high heat disrupted electricity supplies and train travel, driving people along the East Coast to parks and public fountains with manual and electronic fans in hand.