Severe heat and humidity clashed with a cold front across much of Minnesota on Friday, leaving a debris field of buckled roads, torn-off roofs, collapsed farm buildings, snapped-off trees and downed power lines but bringing a decisive break from the two-day heat wave.

Storms with winds approaching 80 miles per hour, heavy rain and hail of 2 or more inches in diameter rammed their way from southwestern Minnesota through the St. Cloud area northeast to Hinckley through the afternoon and evening. At least two tornado warnings were posted, and National Weather Service damage assessors are expected to visit areas near Olivia and St. Cloud today to determine whether tornadoes in fact touched down.

The start of the Minnesota Twins-Milwaukee Brewers game at Target Field in Minneapolis was delayed for two hours as the storms approached, then brought heavy rain just after 8 p.m. Francisco Liriano finally threw the first pitch shortly after 9 p.m.

At the Star Tribune, about a mile from the stadium, .22 inches of rain fell between 8:15 and 8:45 p.m. St. Cloud reported 0.9 inches of rain by 7 p.m.

Stearns County emergency operations manager Marvin Klug said that despite an apparent touchdown near Rockville, where a significant number of trees were blown over, the damage apparently was caused by straight-line winds. No injuries were reported.

Highways and city streets in Renville County also were littered with trees and downed power lines, and some roads were being closed Friday night, said emergency operations manager Mike Hennen. County emergency communications were running on backup power; in Olivia, Bird Island and other cities, "massive amounts" of trees were down, he added.

The storms were triggered in part when the rising warm surface air, capped for days by colder air above, broke through the cap and accelerated into high levels of the atmosphere. Water vapor cooled as it rose, condensing to form rain and hail. The Twin Cities endured a high temperature of 99 Friday, one degree shy of a record. But by nightfall, the temperature had dropped to 75 as heavy rain fell. At St. Cloud, the temperature dropped 30 degrees, from 96 to 66, between 4 and 7 p.m.

The intense heat caused pavement to pop in at least seven locations in the metro area, including on Interstate 94 near Dowling Avenue N., and at one place on I-94 in St. Cloud in midafternoon, just as drivers were heading out of the Twin Cities for the holiday weekend.

Minnesota Department of Transportation spokesman Kevin Gutknecht said the few repair crews available during the state government shutdown had repaired all the pavement heaves by early evening.

Bill McAuliffe • 612-673-7646