CHICAGO - A massive and dangerous winter snowstorm blanketed the US Midwest on Thursday, grounding planes and making roads and highways impassable as travelers gear up for the Christmas holiday.
The region's first big storm of the season dumped more than a foot (30 centimeters) of snow in parts of Wisconsin, Iowa and Minnesota overnight and more was expected as the powerful system moved slowly eastward.
Winds with gusts as high as 50 miles (80 kilometers) per hour felled trees and power lines, leaving tens of thousands of homes in the dark and cold.
Snow drifts reached as high as four feet (121 centimeters) in some places and visibility was down to zero as heavy white flakes flew through the air, the National Weather Service reported.
"Travel will be dangerous and potentially life threatening if you become stranded," the agency warned.
"Emergency services and rescues could be halted for a period of time during the height of the storm."
Wisconsin Governor Scott Walker issued a state of emergency and called up the National Guard ahead of the storm "to make sure Wisconsin is prepared for whatever this winter storm may bring."
Soldiers were prepositioned to help stranded motorists, but most were smart enough to stay home and the state highway patrol reported "no major crashes with only a few weather related vehicle run-offs" overnight.
A regional energy company said the storm had cut power to more than 40,000 households and businesses in Iowa, where nearly a foot (30 centimeters) of snow had fallen in the capital, Des Moines.
Blizzard warnings were also issued in Nebraska, Missouri and Illinois.
"Highways were a mess because it started as rain then changed to snow," Pat Slattery, a spokesman for the National Weather Service who works in Kansas City, Missouri, told AFP.
"I have 30 miles to get to work it took me an hour and a half this morning."
The storm had also dumped more than two feet of snow in parts of the western US, including Washington state and Wyoming on Wednesday.
Airlines cancelled more than 150 flights and passengers also encountered delays of up to four hours at Chicago's bustling O'Hare airport, one of the busiest in the world.
Rain made Chicago's runways and roads slick morning and heavy snow was anticipated to strike around 3 pm (2100 GMT) -- just in time to snarl the evening commute.
Delays and cancellations could affect travel across the country, especially since many passengers need to change planes in Chicago -- and even if they do not, their aircraft may have to pass through there.
Flights through smaller airports in Iowa, Missouri, South Dakota, Wisconsin and Minnesota were also cancelled Thursday morning.
Two major airlines, Delta and United, issued travel alerts allowing passengers to change their tickets without fees for travel through affected areas.
Further south, the weather service warned of a "life-threatening blizzard" that was located over central Missouri on Thursday morning and heading into western Illinois by morning.
"This will result in life threatening conditions and nearly impossible travel overnight through today," the bulletin warned.
"Falling trees may also occur to due heavy snow accumulation on trees and high winds."
Many schools across Nebraska and Iowa were closed or opened late.