Temperatures have soared past the 100-degree mark, making it the hottest day the Twin Cities area has seen in 23 years.
The high temperatures also helped push ozone levels up, prompting officials to issue an air pollution health alert through midnight. Children, the elderly and people with respiratory issues were advised to limit outdoor activity.
Ozone is produced when pollutants from things like cars and lawn mowers mix with the air, so the Minnesota Pollution Control Agency encouraged people to postpone vehicle trips and reduce engine idling. Limiting use of gasoline-powered equipment, paint, solvents and burning wood can also make a difference, officials said.
MPCA Air Quality Specialist Cassie McMahon said events elsewhere can also affect Minnesota's ozone levels.
"Across the country all the central United States is being affected by the smoke from the wildfires in Arizona. And part of the emissions from those fires do actually contribute to the formation of ozone," she said.
McMahon said it's the first ozone air alert for the metro area since 2007.
"We're out of practice on the ozone alerts a little bit," she said. "Mainly we've been issuing air quality alerts for fine particle pollution, which is a pollutant that can happen year round. But ozone is definitely a signature on hot, sunny, summer days."
McMahon said people in suburban and exurban communities often have the highest ozone concentrations due to the way the chemicals are transported by the wind.
A cold front will move through the Twin Cities on Wednesday, bringing a cleaner air mass to the region. Temperatures are also expected to drop into the 70s.
According to the National Weather Service, the temperature at Minneapolis-St. Paul International Airport hit 102 degrees Tuesday afternoon. That's the hottest it's been in the Twin Cities since 1988.
An excessive heat warning remained in effect until Wednesday morning.
The weather service said the previous record for June 7 was 95 degrees set in 2004. The all-time record for the month of June is 104 degrees, set in 1934, and forecasters said there's still a chance temperatures could get that high.
The heat forced a delayed start for the State Boys' Lacrosse Tournament games, which will each be played an hour later. The Minnesota State High School League said officials might schedule one-minute water breaks during each four minutes of play if necessary, as turf temperature will be hotter than the air temperature.
At least two people were treated at Regions Hospital in St. Paul for heat exhaustion Monday, and a third person sought care Tuesday for sunburn, according to a Regions spokeswoman.
Dr. Gary Mayeux, a Regions emergency doctor, said some of the first signs a person is suffering from heat exhaustion is nausea and vomiting. In extreme cases, people can be so dehydrated they aren't sweating.
"A lot of people know what to look for when they're looking at a severely dehydrated patient, but you want to pay extra close attention, especially to kids and the elderly who might not be as vocal about how they're feeling," Mayeux said.
Other symptoms can include a fast pulse or confusion, he said.
Monday's 97-degree mark caused highway pavement to buckle in 28 different places in the Twin Cities. All the roads have since been fixed, but MnDOT officials were watching for a repeat today, said spokesman Todd Kramascz.
"The right amount of volume on that roadway, given that temperature and humidity can cause breakup," he said.
No problems had been reported on Tuesday so far.
(MPR reporter Tim Nelson contributed to this report.)