More than 1.6 inches of rain fell in Grand Forks in less than half an hour, the National Weather Service said.

"I've never seen a hurricane, and that's the closest I want to get to one," said Kevin Dean, Grand Forks public information officer. "Trees were sideways. I have no idea how some of them lasted."

The city lost more than 3,000 trees. "They came down on cars, power lines, rooftops, transformers," Dean said. "It was a mess."

Thirteen people were treated at Grand Forks' Altru Hospital for minor injuries, a spokeswoman said. More than half of Xcel Energy's 22,000 Grand Forks customers lost power. About 7,900 still were without power at noon Thursday. "Little by little, you're seeing traffic lights come on," Dean said.

Sirens went off about five minutes before the storm hit, bringing a sharp and sloppy end to an extended heat spell. The hardest-hit area included the cities' downtowns, where some glass storefronts were blown out -- leaving scenes recalling the aftermath of the 1997 flood.

In East Grand Forks, the sudden windstorm also uprooted trees and damaged roofs, and it blew out a large plate-glass window in the mayor's office in the new City Hall, which Mayor Lynn Stauss hadn't moved into yet. The old City Hall was a casualty of the '97 flood.

"When it hit, the temperature must have dropped 30 degrees," said Craig Mattson, East Grand Forks city administrator. "The rain was a sprinkle at first, then sheets coming sideways. Running back to my house, I just missed getting hit by a branch 30 inches long, 8 inches in diameter."

At least two dozen utility poles were knocked down in East Grand Forks, and power went out throughout the city of 8,000 people. With help from utility crews from Thief River Falls and Moorhead, Minn., power was restored to about 90 percent of the city by noon Thursday, utility manager Dan Boyce said.

A transmission station might be out a week, he said, and that could affect power to the American Crystal Sugar plant in East Grand Forks.

In Crookston, Minn., "there's a lot of debris on city streets, trees down on power lines and a lot of roof damage," said Mark Fontaine of the Polk County emergency management office.

"We got it in the south end of the county and the north end, all the way from west to east," he said. "We've had reports of grain bins blown away in rural areas."

Roofs were damaged on several buildings at the University of Minnesota-Crookston, and Otter Tail Power Co. wasn't able to restore power to campus until 2 p.m. Thursday. But the biggest damage was to campus aesthetics, Chancellor Don Sargeant said.

"We had a very beautiful campus, and to visitors the mall still will look very nice with all the flowers," he said. "But nearly all the big trees were blown down, and they were such an important part of our life."

Grand Forks opened an emergency shelter at the city's events center and asked people to limit water use as the city rotated backup generators.

Gov. John Hoeven dispatched about 30 National Guard troops to Grand Forks with front-end loaders and dump trucks to help with debris removal.

The storm resulted when two strong cells collided in east-central North Dakota, the Weather Service said. Storms also snapped trees and power lines and damaged a fourth of the homes in Hillsboro, 40 miles south of Grand Forks.