An April snowstorm stretched from Utah into Minnesota, and could dump as much as 16 inches of snow by the end of Tuesday in areas of Wyoming and South Dakota, CNN said.
Residents in and around Denver were braced for frigid temperatures and another wintry blast.
But before the snow hits parts of Colorado, officials said firefighters bested a 2,600-acre fire in Sterling County, and then a suspected tornado ripped through a home in neighboring Washington County.
The National Weather Service issued a blizzard warning in Arapahoe and Adams counties where temperatures could fall into the single digits Tuesday night.
Meanwhile, strong thunderstorms were forecast for the Midwest, while the Ohio Valley and the Southeast were expecting unusually warm weather, CNN said.
The Denver Post said 535 flights at Denver International Airport were canceled Tuesday with as much as 5 inches of snow expected in the metro area falling on top of roads that had been wet with rain and likely to freeze over.
The city's fleet of 70 plows were fully deployed Tuesday morning, public works officials told the Post. They tackled freezing roads in frigid conditions. The temperature was 28 degrees in Denver at 5:30 a.m. Tuesday but winds made it feel more like 1 below zero outside.
Accuweather.com said Denver underwent a 26-degree dip in temperatures in just two hours overnight Tuesday.
As the storm stretched into South Dakota, as much as an inch of ice accumulated, bringing down trees and power lines in Sioux Falls, Accuweather.com said.
More than 200 hundred schools were closed.
In the Midwest, flood watches and warnings were in effect Tuesday for most of Wisconsin, which could experience freezing rain later in the week, CNN said.
The National Weather Service said severe thunderstorms and isolated tornadoes were possible across the central and southern Plains to the mid- and lower-Mississippi Valley.
AccuWeather.com said reports came in that Interstate-15 between Bountiful and Layton in Utah was closed to high profile vehicles because of strong winds. Wind gusts topped 60 mph in Farmington.