Updated

South Dakota students are used to extreme cold and having classes called off because of winter blizzards, but the weather that caused their school day to be cut short Wednesday was intense for a different reason: the triple-digit temperatures.

More than two dozen school districts across the state shut down early Wednesday as temperatures rose above 100 degrees, turning classrooms into saunas.

"The major factor in the decision is the safety and welfare of students and staff members. It's tough to learn in an environment when a room is 100 degrees," said Eureka Superintendent Bo Beck, whose north-central South Dakota district joined others in dismissing students a few hours early because their classrooms lack air conditioning.

Eureka and other districts have called off classes due to late-summer heat in past years, but school closures are more common in winter months when snow, frigid temperatures and howling winds make travel unsafe, Beck said.

Scott Doering, a meteorologist with the National Weather Service in Aberdeen, said high temperatures Wednesday were expected to range from the low 90s in northeastern South Dakota to as high as 107 in the center of the state as a ridge of high pressure made the northern and central Plains area the nation's hotspot.

Some places in central South Dakota could break or come close to breaking records before temperatures start to drop to the 80s and lower 90s Thursday, Doering said.

He said temperatures topping 100 sometimes persist in South Dakota, even into September. "It's unusual, but not highly unusual," he added, referring to Wednesday's heat.

Don Hotalling, superintendent for the Stanley County School District, said all students in Fort Pierre were being sent home at 1 p.m. because some classrooms are not air-conditioned. That problem will be solved after a new building is completed next year, he said.

"With 106 degrees forecast for today, we knew it really was going to be miserable for some of the students," Hotalling said. "With the humidity and the heat, it's very uncomfortable. Not much learning is going to be going on later in the afternoon, when it gets hotter."

Stanley County eighth-grader Madison Bogue was happy her Fort Pierre school ended the day early. "It's really awesome. It's better than sitting in there all day," the 13-year-old said.

The district used fans to try to cool buildings Tuesday, when a lot of parents picked up their kids and took them home to beat the heat, Hotalling said. Staff encouraged students to drink plenty of water, but some students complained Tuesday of headaches, he said.

Deputy state Education Secretary Mary Stadick Smith said she didn't know how many schools were closing because of the heat, but at least two dozen schools from northeastern South Dakota to Rapid City in the west let radio and television stations know of early closures.

"Typically in South Dakota, schools are closed because of cold weather and blizzards that kind of thing, so it is a little unusual," Stadick Smith said.

Schools will not have to make up the missed time as long as they meet annual requirements for hours spent in classrooms, she said.

The Rapid City Journal reported that schools in that city also were closing early because 15 of the 25 public schools do not have air conditioning.

"When we start reaching temperatures above 90 degrees in classrooms, we have concerns as to trying to do something to relieve that stress on the teachers and the students that have been trying to work in those rooms," Rapid City Area Schools Superintendent Tim Mitchell told the newspaper.

Principal Robin Gillespie said teachers at Rapid City's Wilson Elementary have been beating the heat with fans, low lights, water breaks and Popsicles.

Many South Dakota residents seemed to take the heat in stride.

Retiree Steve Wegman of Pierre said he doesn't mind the heat, and he planned to ride his motorcycle later Wednesday. "This is my kind of weather," he said.

Jayne Parsons, a wellness consultant in Pierre, said she's ready for fall but knows winter can be tough.

"When it's 30 below, I'll have to remind myself this wasn't so nice either," Parsons said.