Strong storms with damaging winds and baseball-sized hail pummeled North Texas on Tuesday morning as much of the U.S. recovered from severe weather, including tornadoes, that killed at least 25 people during the Memorial Day holiday weekend.

Widespread power outages were reported in the region, which includes Dallas and Fort Worth, where an oppressive, early-season heat wave reaching into triple digits added to the misery. Nearly 800,000 customers lacked electricity Tuesday, according to PowerOutage.us.

Voters in the state’s runoff elections found some polling places without power. Roughly 100 voting sites in Dallas County were knocked offline. Dallas County Judge Clay Jenkins declared a disaster area and noted that some nursing homes were using generators. “This ultimately will be a multi-day power outage situation,” Jenkins said Tuesday.

More rough weather and heavy rains were forecast for the Dallas area Tuesday night.

Destructive storms over the weekend caused deaths in Texas, Oklahoma, Arkansas, Missouri, Kentucky, North Carolina and Virginia.

Seven people were killed in Cooke County, Texas, from a tornado that tore through a mobile home park Saturday, officials said, and eight deaths were reported across Arkansas.

Two people died in Mayes County, Oklahoma, east of Tulsa, authorities said. The injured included guests at an outdoor wedding. A Missouri man died Sunday after a tree limb fell onto his tent as he was camping.

Kentucky Gov. Andy Beshear said at a news conference Monday that five people had died in his state.

A possible tornado damaged a high school and a half-dozen homes in Pennsylvania on Monday night. No injuries were reported, but school was canceled in Mahanoy City, Pennsylvania, said David Truskowsky, spokesperson for the city’s fire department.

Roughly 160,000 homes and businesses lacked electricity Tuesday following the weekend storms in Kentucky, Arkansas, West Virginia and Missouri.

It has been a grim month of tornadoes and severe weather in the nation’s midsection.

Tornadoes in Iowa last week left at least five people dead and dozens injured. Storms killed eight people in Houston this month. April had the second-highest number of tornadoes on record in the country. The storms come as climate change contributes in general to the severity of storms around the world.

Late May is the peak of tornado season, but the recent storms have been exceptionally violent, producing very strong tornadoes, said Victor Gensini, a meteorology professor at Northern Illinois University.

“Over the weekend, we’ve had a lot of hot and humid air, a lot of gasoline, a lot of fuel for these storms. And we’ve had a really strong jet stream as well. That jet stream has been aiding in providing the wind shear necessary for these types of tornadoes,” Gensini said.

Harold Brooks, a senior scientist at the National Severe Storms Laboratory in Norman, Oklahoma, said a persistent pattern of warm, moist air is to blame for the string of tornadoes over the past two months.

That air is at the northern edge of a heat dome bringing temperatures typically seen at the height of summer to late May.

The heat index — a combination of air temperature and humidity to indicate how the heat feels to the human body — neared triple digits in parts of south Texas on Monday. Extreme heat was also forecast for San Antonio and Dallas.

In Florida, Melbourne and Ft. Pierce set new daily record highs Monday. Both hit 98 degrees. Miami set a record high of 96 on Sunday.