Strong winds unexpectedly blew through Hennepin County Monday night, tearing down power lines, snapping tree branches and overturning boats on Lake Minnetonka.

Hennepin County declared a severe thunderstorm warning for the southwestern parts of the county at 7:41 p.m., lasting through 9 p.m. Monday night.

“Damaging wind is the primary threat. Move into a secure location and continue to stay weather aware,” tweeted Hennepin County Emergency Management.

By 9:45 p.m., Xcel Energy reported 242 power outages in the metro area, with 195 of those in the west metro.

The National Weather Service warned residents of 60-mile-an-hour wind gusts and penny-sized hail.

“As the showers moved out, the winds kicked in,” said Bill Borghoff, lead forecaster with the National Weather Service. “The wind was strongest in the Lake Minnetonka area and then gradually diminished as it got toward the airport.”

Borghoff said the gusts were somewhat of a surprise and “not a traditional thunderstorm threat.” Dry Wisconsin air mixed with rain, causing the air to become cooler and condensed. Then that air dropped to the ground, he said.

On the The Lake Minnetonka Fan Club Facebook page, members posted pictures of damaged boats and docks. Cindy Larson wrote that in 11 years, she had never seen such extreme conditions.

Rebekah Todd posted a video to Facebook of the wind overturning boats on Lake Minnetonka: “Several boats under water and docks being ripped apart!” she wrote.