Thousands of Grand Forks residents were ordered to take shelter Monday, June 8, as a tornado-warned supercell passed by the area.

Grand Forks National Weather Service meteorologist Vince Godon said that it's common for storm radar to detect rotation in thunderstorm clouds. But when spotters on the ground observe cloud rotation in a supercell in addition to the radar, that's when it's clear there is potential for a tornado to form.

That was the case Monday, when cloud rotation was detected by spotters around 5:12 p.m. above Emerado, about 16 miles west of Grand Forks. A tornado warning was issued for an area that included Grand Forks, prompting the city's siren system to be activated for the duration of the warning, about a half hour. The warning was canceled when it became clear that the supercell would miss Grand Forks, passing by on its west side.

"Basically, that rotation in the thunderstorm itself has to get down to the surface somehow, and that's a very challenging thing for storms to do," said Aaron Kennedy. "In this case, it couldn't quite do that, so you could see some rotation at the cloud level, but (it) never got all the way down to the surface."

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Kennedy, an associate professor with the UND atmospheric sciences department, said his students observed a funnel cloud associated with the storm over Middle River, Minn., but Godon said the NWS is still investigating whether any tornadoes touched down or not.

"The winds weren't quite quite good enough to allow it to go nuts and produce lots of tornadoes," he said. "But they tried to produce a tornado a few times, especially west of town."

Kennedy, who spent Monday evening chasing the storm, said that supercells are unique from other thunderstorms in their longevity, and this storm was no exception, forming over Emerado and lasting several hours to reach at least Lake of the Woods.

He said the storm was always following a clear path that slightly missed Grand Forks, but said supercells can be known to turn suddenly as they strengthen. If that had happened, damage to the town could have been more severe.

Even without a confirmed tornado, damage to the region was extensive, Godon said. Wind speeds in the region averaged 50 to 70 mph during the storm, and Tuesday morning, there were widespread reports of fallen tree branches. Godon reported he had heard anecdotally about sheds that had blown away, but he said the NWS had yet to receive reports of any serious structural damage.

Minnesota's northwest angle near Roseau also received significant hail damage, with reports of golf ball- and tennis ball-sized hail stones. Godon said there was also reports of basement and agricultural damage near Hallock, Minn., due to 4 to 6 inches of rain during the storm.

Grand Forks, caught in the relatively quiet area between two separate storm systems, received less than a half-inch of rain and no reports of hail. Wind speeds at the Grand Forks Airport reached 63 mph.

The tornado warning prompted some confusion in town, however. Becky Ault, director of the Grand Forks County Public Safety Answering Point, said about 10 people contacted dispatchers because they were unsure of where to go for the warning.

In the case of a tornado warning, residents should take shelter in their basement. If they don't have a basement, and, if conditions outside are safe, Ault said residents should travel to one of the city's two designated shelters: Noren Hall located at 450 Stanford Road on the UND campus, and Sharon Lutheran located at 1720 S. 20th St.

She said she suspects some of the confusion this year was due to a recent change in designated shelters. This year, for the first time, Red River School is no longer a designated shelter and was replaced by Sharon Lutheran.

Godon, a longtime Grand Forks resident, said it's somewhat rare for the city sirens to be activated, and Ault said it's even rarer that the sirens are activated for as long as a half hour, as they were Monday. But she said that, in an area that can be prone to potentially dangerous cloud rotations in the summer months, sirens are usually activated at least once a year for a tornado warning.

Sirens are also activated at 1 p.m. on the first Wednesday of every month, except for winter months, as a test.

"We kind of forget because we start dealing with winter and winter weather ... and then we get into summer and we're enjoying it. But there's still that severe summer weather awareness that we need to bear in mind. So there's good and bad with every season," Ault said.