SIOUX FALLS, S.D. — Blizzards rolled into parts of Wyoming and South Dakota on Friday, bringing the snow-savvy states to an unseasonably early winter standstill and even forcing a tourist town to cancel its annual Octoberfest’s polka-dancing bar crawl.

A foot of snow had fallen in western South Dakota’s scenic Black Hills by early Friday, though residents were bracing for as much as 3 feet of snow and wind gusts of up to 70 mph. The storm system also spawned a tornado in Nebraska, blanketed Colorado’s northern mountains with snow and was threatening to push strong thunderstorms as far east as Wisconsin.

Julie Lee said she and fellow members of her White Rose Band were accustomed to snow, just “not for the fourth of October.” They had barely unloaded their instruments in South Dakota’s Old West casino town of Deadwood before the wet, heavy snow started falling and closed part of Interstate 90, the area’s only interstate.

“Our car is like an igloo,” said Lee, who sings and plays the clarinet and saxophone for her North Dakota-based polka band. “I’m glad we got everything out.”

The weather, which even forecasters acknowledged was rare, prompted Deadwood officials to postpone their annual Octoberfest, including Friday night’s dancing-and-singing pub crawl and Saturday’s Wiener Dog Races and Beer Barrel Games. But Lee said she and her accordion-playing husband, who had planned to set up in a casino bar, still planned to entertain stranded guests because “you can only gamble for so long.”

Officials were warning drivers to stay off the roads in the Black Hills and in eastern Wyoming, where reports of 5 to 10 inches of snow were common. Forecasters urged people trying to travel to carry survival kits and to stay in their vehicles if they get stranded.

“I’ve lived in Wyoming my whole life and I’ve never seen it like this this early,” Patricia Whitman, shift manager at the Flying J truck stop in Gillette, said in a telephone interview Friday morning. She said her truck stop’s parking lot was full of travelers waiting out the storm.

“I know several of the businesses nearby are completely closed because they can’t even get workers into work — it’s pretty nasty,” she said.

The snow also snapped tree limbs that knocked out power lines in parts of the state, causing thousands of people to lose power.

It was a similar scene at the typically bustling Pilot Travel Center in western South Dakota near Rapid City, about 40 miles southwest of Deadwood. It was like a ghost town Friday morning, which store general manager John Barton attributed to drivers likely heeding forecasters’ warnings to stay off the roads.

The blowing snow was picking up outside the truck stop along Interstate 90, which was closed for about 30 miles because of the weather. Conditions were expected to deteriorate throughout the day.

“Yesterday we were really busy,” Barton said. “I think a lot of people got ahead of it.”

Although early October snowfalls aren’t unusual for the region, a storm of such magnitude happens only once every decade or two on the Plains, National Weather Service meteorologist Steve Trimarchi said.

“I couldn’t say when the last time we’ve had one like this. It’s been quite a while,” Trimarchi said.

Large hail and powerful winds were forecast to hit northwest Oklahoma later Friday, while heavy rain settled in parts of Iowa and was expected to swoop northeast across the region into Wisconsin.

In Nebraska, a tornado that touched down Thursday night damaged homes and businesses in several communities, knocked out power and toppled trees. But no injuries have been reported.

Snow also was still falling across northern Colorado on Friday, though no major problems were being reported. Forecasters expect snow to be the heaviest in the higher mountains, while the Denver metropolitan area was reporting rain turning into snow.