The Associated Press reported that about 40 people, mostly truckers, were stalled at Moorcroft, Wyo., along I-90.
A 60-mile section of I-90 was closed from Moorcroft to just inside South Dakota near Spearfish, along with U.S. 85 from Newcastle, Wyo., to near Lead, S.D.
The National Weather Service said a total of 3 feet of snow could fall in parts of South Dakota's Black Hills, and wind gusts of up to 49 mph have been reported.
In southeastern Wyoming, a 50-mile stretch of I-80 was closed between Cheyenne and Laramie.
At a Conoco truckstop in Cheyenne, the parking lot was packed with truckers waiting for the highway to reopen.
"It's costing me, for every 10 hours I sit, about $130. Not counting the fuel," Bill
Spencer of White City, Ore., told the AP.
Winter storm warnings are in effect for parts of eastern Wyoming, western South Dakota and the mountains of northwestern Colorado.