A tornado that struck Nebraska Friday, injuring 15 people and flattening buildings, may have reached a wind velocity of up to 200 miles per hour, the National Weather Service said on Saturday. It was part of an unusual early autumn storm system that also dropped 3 feet of snow in South Dakota and Wyoming. The twister produced EF2 to EF3 damage in the small town of Wayne and possibly EF4 damage at a business park there, the National Weather Service said. An EF4 tornado has wind speeds of 166 to 200 mph, according to the weather service. Damage in Wayne will run into the millions of dollars, Mayor Ken Chamberlin said on Saturday.