Forecasters warned people outdoors to take precautions as triple-digit temperatures prompted heat advisories across much of the southern U.S., 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 that 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.

Louisiana Governor John Bel Edwards declared a state of emergency for the north and central parts of the state after strong winds and severe weather caused widespread power outages on Saturday. On Sunday evening, more than 515,000 people were without electricity in Texas, Oklahoma, Louisiana, Arkansas, and Mississippi, according to PowerOutage.us.

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 the 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 degrees Fahrenheit (42 degrees Celsius) and 112 degrees (45 degrees Celsius) 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 Fahrenheit (43.5 degrees Celsius) in Phoenix.

Winds were forecast to gust from 30 mph to 40 mph (48-64 kph) on Sunday east of Flagstaff, Arizona, along the Interstate 40 corridor and up to 50 mph (80 kph) on 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 on Saturday. Arizona 83 reopened on 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.

Much of Nevada was under a high-wind advisory with gusts up to 55 mph (88 kph) and blowing dust that could hamper visibility on highways, the weather service said.

(Cover images via VCG)

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