Forecasters on Sunday warned people celebrating Father’s Day outdoors to take precautions as triple-digit temperatures prompted heat advisories across much of the American South, triggered thunderstorms that knocked out power from Oklahoma to Mississippi, and whipped up winds that raised wildfire threats in Arizona and New Mexico.

A suspected tornado struck near Scranton, Arkansas, early Sunday, destroying chicken houses and toppling trees onto homes, the National Weather Service said. There were no immediate reports of serious injuries.

Meteorologists said dangerous and potentially record-breaking temperatures would continue into midweek over southern Texas and much of the Gulf Coast. Storms producing damaging winds, hail and possibly tornadoes could strike the lower Mississippi Valley.

“If you have outdoor plans this #FathersDay, don’t forget to practice heat safety! Take frequent breaks, stay hydrated, NEVER leave people/pets alone in a car!” the weather service office in Houston tweeted.

Louisiana Gov. John Bel Edwards declared a state of emergency for north and central parts of his state after strong winds and severe weather caused widespread power outages Saturday. On Sunday, more than 450,000 people were without electricity in Texas, Oklahoma, Louisiana, Arkansas and Mississippi, according to PowerOutage.us, a website that tracks outages.

Catherine Haley was hosting her six grandchildren, ages 7 to 13, in Shreveport, Louisiana, when the storm knocked out electricity to her block and many surrounding neighborhoods. Haley, who has trouble breathing, said they draped damp towels around their necks to try and stay cool, but when the heat became unbearable the family took refuge at a cooling center set up by the city.

“I am so grateful. We tried the first day to stay at home and they were just so uncomfortable. And then I have COPD, and the heat really took effect on me as well,” Haley, 64, said Sunday.

She said five of her grandchildren had just arrived from Houston for the summer when the storm hit, causing widespread damage. “Nice little welcome for them,” she joked.

In Florida, the weather service issued another heat advisory Sunday, this time mainly for the Florida Keys. Forecasters said heat index readings – the combination of high temperatures and oppressive humidity – could reach between 108 and 112 degrees Fahrenheit in places such as Key Largo, Marathon and Key West.

“These conditions will cause increased risk of heat illness for people outdoors or in non-air conditioned spaces,” the weather service said in a bulletin.

In the Southwest, where fire crews are battling multiple wildfires in Arizona and New Mexico, forecasters said triple-digit temperatures and gusty winds would lead to critical fire weather over the next couple of days. Sunday promised to be the hottest day of the year in Arizona, with highs up to 110 degrees in Phoenix.

Winds were forecast to gust from 30 to 40 mph on Sunday east of Flagstaff, Arizona, along the Interstate 40 corridor and up to 50 mph Monday, creating potentially critical fire weather across much of northeast New Mexico.

A large brush fire that broke out Friday afternoon south of Tucson, Arizona, shut down a state highway Saturday. Arizona 83 reopened Sunday, and no homes were in immediate danger, authorities said.

The prolonged closure took a toll on local businesses during what’s usually a busy Father’s Day weekend in an area with recreational lakes and reservoirs.

Dena Proez said the only business at her Corner Scoop ice cream shop along the highway in Sonoita was serving a few travelers who stopped to get updates on the fire – “and feeding all the firefighters.”

Much of Nevada was under a high wind advisory with gusts up to 55 mph with blowing dust that could hamper visibility on highways, the weather service said.

Associated Press writers Kim Chandler in Montgomery, Alabama; Curt Anderson in St. Petersburg, Florida; and Christopher Weber in Los Angeles contributed to this report.