In Wyoming, stretches of Interstates 25 and 80 were closed for parts of the day, and blowing snow made driving dangerous along other highways. About 180 miles of I-25 between Cheyenne and Casper were under whiteout conditions.
"We haven't really had bad days like today where everybody is stuck and nobody can go anywhere," said Sam Blaney, who was working the service counter at the Petro truck stop in Laramie.
About two dozen truckers and other motorists had taken refuge at the truck stop to wait out the storm, Blaney said.
Eastbound I-80 from Cheyenne to Big Springs, Neb., was closed Tuesday night. Wyoming transportation officials said their Nebraska counterparts had warned it could be midday Wednesday before the stretch reopens.
Meanwhile, freezing rain, snow and strong winds were hitting Kansas and South Dakota, where many local elections were postponed. Some schools in Minnesota dismissed students early as travel conditions deteriorated.
I-90 was closed between Rapid City and Sioux Falls, S.D., as visibility dropped to zero to near-zero on snowy, icy roads.
Strong wind gusts caused 21 train cars to derail Tuesday in eastern Nebraska, west of North Bend, Union Pacific railroad spokesman Mark Davis said. No injuries were reported.
In Denver, about 6.5 inches of snow fell at the airport, but the weather prompted nearly 500 flight cancellations and deicing planes delayed departures. Flights going to Chicago's O'Hare International Airport, meanwhile, were being delayed an average of nearly four hours because of dense fog.
Many areas of Wyoming and western Nebraska received more than a foot of snow. In western Nebraska, road crews reported 8- to 9-foot drifts.
April snowstorms aren't unusual in Wyoming and the Rocky Mountain West, but the storm comes after a rather tame winter in many areas. Some areas had daytime temperatures in the teens and 20s.
The National Weather Service said Cheyenne's high of 12 degrees Tuesday was the coldest on record for April 9. The previous record was 23 degrees set in 1997.
"I'm pretty confident that this particular storm is more widespread and has caused more travel problems and closures than any storm we've had this calendar year certainly," said Bruce Burrows, spokesman for the Wyoming Department of Transportation.
The blustery storm hit the U.S. West Coast by blowing through California and Arizona first, then moving into Colorado on Monday night. Two tornadoes were reported near Akron on eastern Colorado's plains, though forecasters had not confirmed the twisters. A trailer home rolled over onto its top, a roof blew off a barn and six power poles were toppled, Washington County undersheriff Jon Stivers said.
A motorcycle dealership partially collapsed in Pueblo, Colo., where winds gusted to 64 mph.
In Wyoming's Sweetwater County, wind gusts up to 71 mph damaged a marina at Flaming Gorge Reservoir and broke windows at the Western Wyoming Community College in Rock Springs, according to the National Weather Service.
Hundreds of customers in Wyoming and Colorado lost power as the wind and wet snow downed wires. The same storm toppled trees in San Francisco, produced gusts over 80 mph in southern California, fanning wildfires, and kicked up a dusty haze in Phoenix on Monday.
Associated Press writers Colleen Slevin and Alexandra Tilsley contributed to this report from Denver.