Heavy snow also expected in the Dakotas.
Forecasters said Denver could get as much as 11 inches of snow and South Dakota more than a foot, with snow stretching as far north and east as Minnesota and Nebraska.
Temperature plunges 55 degrees in 17 hours
In Denver, the temperature plummeted from 71 degrees at 2 p.m. Monday to 16 degrees at 7 a.m. Tuesday, with a wind chill of 1.