HOUSTON (AP) — As the Houston area works to clean up and restore power to thousands after deadly storms, it will do so Saturday under a smog warning and as all of southern Texas starts to feel the heat.

The National Weather Service in Houston warned that with temperatures hitting around 90 degrees (32.2 C) this weekend, people should know the symptoms of heat exhaustion. ”Don’t overdo yourself during the cleanup process,” it said in a post on the social platform X.

The balmy weather is a concern in a region where more than 555,000 homes and businesses remained without electricity Friday night — down from nearly 1 million, according to PowerOutage.us. Fierce storms Thursday with winds of up to 100 mph (161 kph) blew out windows downtown, while a tornado touched down near the the northwest Houston suburb of Cypress.

At least four people were killed when the storms swept through Harris County, which includes Houston. Harris County Judge Lina Hidalgo said Friday that it could take “weeks” for power to be restored in some areas.

With multiple transmission towers down, Hidalgo urged patience. Another 26,000 customers were without power in Louisiana, where strong winds and a suspected tornado hit, down from a peak of 215,000.

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“We are going to have to talk about this disaster in weeks, not days,” Hidalgo said.

She said she had heard “horror stories of just terror and powerlessness” as the storm came through. The weather service also reported straight-line winds of up to 100 mph (161 kph) in the suburbs of Baytown and Galena Park.

The Houston Health Department said it would distribute 400 free portable air conditioners to area seniors, people with disabilities and caregivers of disabled children.

In addition to the heat, the Houston area has also been warned about poor air quality over the weekend. While to the east, heavy rainfall was possible in eastern Louisiana into central Alabama, while parts of Louisiana were warned of the risk of flash floods through Saturday.

The widespread destruction brought much of Houston to a standstill. Trees, debris and shattered glass littered the streets. One building’s brick wall was ripped off.

School districts in the Houston area canceled classes Friday for more than 400,000 students and government offices were closed. City officials urged people to avoid downtown and stay off roads, many of which were flooded or lined with downed power lines and malfunctioning traffic lights.

Houston Mayor John Whitmire warned that police were out in force, including state troopers sent to the area to prevent looting. He said the speed and intensity of the storm caught many off guard.

“Most Houstonians didn’t have time to place themselves out of harms way,” Whitmire said at a news conference.

Noelle Delgado’s pulled up Thursday night to Houston Pets Alive, the animal rescue organization where she is executive director to find the dogs and cats — more than 30 in all — were uninjured, but the awning had been ripped off, the sign was mangled and water was leaking inside. She hoped to find foster homes for the animals.

“I could definitely tell that this storm was a little different,” she said. “It felt terrifying.”

Yesenia Guzmán worried whether she would get paid with the power still out at the restaurant where she works in the Houston suburb of Katy.

“We don’t really know what’s going to happen,” she said.

Whitmire signed disaster declaration, which paves the way for state and federal storm recovery assistance. President Joe Biden also issued a disaster declaration, his for seven counties in Texas, including Harris, over severe storms, straight-line winds, tornadoes and flooding since April 26. His action makes federal funding available to people affected by the storms.

Emergency officials in neighboring Montgomery County described the damage to transmission lines as “catastrophic.”

High-voltage transmission towers that were torn apart and downed power lines pose a twofold challenge for the utility company because the damage affected transmission and distribution systems, according to Alexandria von Meier, a power and energy expert who called that a rare thing. Damage to just the distribution system is more typical, von Meier said.

How quickly repairs are made will depend on a variety of factors, including the time it takes to assess the damage, equipment replacement, roadwork access issues and workforce availability. Centerpoint Energy deployed 1,000 employees on Friday and had requested 5,000 more line workers and vegetation professionals.

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Associated Press reporters Jamie Stengle in Dallas, Valerie Gonzalez in McAllen and Lisa Baumann in Bellingham, Washington, contributed.