Maps show where extreme humidity and 90- or 100-degree temperatures will affect about 255 million people across the United States.

Major cities across the United States are preparing for extreme temperatures caused by a heat dome that hit the U.S. Plains on Friday and is expected to expand to much of the rest of the country over the coming days.

Weather forecasters have warned of extreme and dangerous temperatures as a major heat wave sweeps across the central and eastern U.S. states.

Central Pennsylvania is bracing for a significant and dangerous heat wave set to begin Sunday, with temperatures climbing into the 90s and heat index values potentially reaching dangerous levels, prompting an Extreme Heat Watch for multiple counties.

The first day of summer is here, and Mother Nature isn’t wasting any time serving up extreme heat across Northeast Ohio starting this weekend. Astronomical summer begins Friday at 10:43 p.m., and while conditions will be seasonable during the day and into the evening,