(Adds distance of interstate closure, other details)
By Kevin Murphy
Oct 4 (Reuters) - A rare and fierce October snowstorm rolled out over the central Rocky Mountains on Friday, downing trees and forcing closures of state offices and 380 miles (612 km) of Interstate 90 across parts of Wyoming and South Dakota, state highway officials said.
The storm dropped up to 37 inches (94 cm) of snow in parts of the Black Hills region of western South Dakota, according to a Rapid City National Weather Service report.
"It's not normal this time of year, but it is not unheard of," said Cory Martin, meteorologist for the National Weather Service in North Platte, Nebraska. "But this amount of snow for an October storm is on the higher end."
Heavy rain, golf ball-sized hail and winds of 60 to 70 miles per hour (96-112 kph) were expected in Oklahoma along with severe storms in Kansas, the National Weather Service said.
The service, which is running on a reduced staff because of the federal government shutdown, issued blizzard and severe winter storm warnings across the Upper Plains through Saturday morning.
South Dakota Governor Dennis Daugaard ordered state offices closed in the Black Hills and six counties in the southwestern part of the state and said further closures are possible. (Additional reporting by Heide Brandes and Lisa Maria Garza; Editing by David Bailey and Eric Walsh)