The far-reaching storm system stretched from California to Indiana, gathering strength as it raced eastward.
Parts of Kansas, Nebraska, Iowa and Wisconsin were bracing for blizzard conditions and up to 10 inches of snow, according to the National Weather Service.
"The storm system is really strengthening as it goes, and that's usually a recipe for some heavy snowfall and a lot of wind, and that's what we're watching for," said Mike Welvaert of the National Weather Service in La Crosse, Wis.
The storm hit nearly all of the western mountain states on Monday, leaving places like Flagstaff and Reno, Nev., under a thick blanket of snow. Heavy rain raised fears of mudslides in wildfire-devastated Southern California, but no damage was reported. The weather system also snarled traffic and closed schools in Indiana, and crashes caused one death.
In the Phoenix area, fierce wind brought down power lines, left four hospitals temporarily without power and created wide outages. At one point, some 250,000 customers were without power; by early Tuesday, that number was down to about 58,000, a spokesman for Arizona Public Service Co. said.
The storm system lingered over the West on Tuesday.
On Monday, virtually the entire Western region was hit by wintry weather - from subzero wind chills in Washington state to heavy snow that closed schools and government offices in Reno, Nev. Big rigs were left jackknifed across highways in several states.
In New Mexico, two people were killed in traffic accidents blamed on slick conditions, and officials there told snow-clearing crews to prepare for 12-hour shifts as the storm swept south and east.
The National Weather Service said the upper elevations of the Sierra mountains could get up to 3 feet of snow, with up to 4 feet forecast for the mountains of southern Utah.
Reno schools closed, and many state government workers were told to stay home. Chains or snow tires were required across the region. Several flights into and out of Reno-Tahoe International Airport were delayed or canceled.
"Motorists are going to have to chain up," Trooper Chuck Allen with the Nevada Highway Patrol said. "Otherwise, we end up with a parking lot."
In northern Arizona, state officials closed parts of Interstate-17 and I-40, saying early Tuesday that some stretches of the highways were snow-packed and visibility levels were near zero.
The city school district let students out early Monday and canceled classes Tuesday. Northern Arizona University also released students and staff early Monday, in the midst of final exams.
Arizona Department of Transportation spokesman Rod Wigman vowed to keep northern Arizona roads plowed despite a $100 million budget deficit, but advised people to stay home if possible as the brunt of the storm sweeps through.
"When the sun goes down, people need to go home," Wigman said.