Doyle Rice, USA TODAY

A killer snowstorm was sweeping across the Midwest and beyond on Thursday, shuttering schools, clogging highways and bottling up airports for the holiday rush.

Three deaths were reported, including a woman in Utah who died after trying to walk for help when her car became stuck in the blizzard.

Blizzard warnings were in effect from Missouri to Wisconsin, according to AccuWeather meteorologist Mike Smith. The Weather Channel reported that parts of 20 of the lower 48 states are under winter weather advisories -- as far west as Washington state and as far east as New York State.

The southern edge of the storm system brought winds and damaged homes in Arkansas, the National Weather Service said. Tornado warnings remained in effect in Mississippi, Louisiana and Alabama.

In southeastern Wisconsin, where a blizzard warning was in effect and winds of up to 45 mph were expected to create whiteout conditions, sheriff's officials said slick conditions led to at least two fatalities late Wednesday when a driver lost control of his car in Rock County, about 90 miles northwest of Chicago.

The weather service was forecasting "thundersnow" in Milwaukee and the surrounding areas, where snow could fall at the rate of 2-3 inches an hour.

Gov. Scott Walker on Wednesday issued an executive order declaring a state of emergency, which put the state Emergency Government, National Guard, State patrol and other agencies at high alert.

The storm forecast promises much-needed precipitation for the drought-plagued regions, but was bad news for holiday travelers.

Expect delays at airports in the path of the storm and ripple-effect delays in other parts of the nation, AccuWeather meteorologist Alex Sosnowski said. The storm will have a direct impact on Chicago, Detroit and Minneapolis, he said.

Most of the nation's big airlines responded to the storm's threat by Wednesday afternoon, enacting flexible rebooking policies for fliers scheduled to fly into the storm's path.

Chicago's O'Hare is a major hub for both American and United, while Midway is one of the top bases for Southwest. If forecasts hold, both airports are at risk of significant delays developing today and lasting into Friday.

"The heaviest amounts of snow will be across Iowa and into southern Wisconsin," according to a weather service report. "Strong, gusty winds accompanying the storm will bring blizzard conditions, making travel in the area hazardous."

Blizzard warnings were in place late Wednesday in a solid stretch from near Denver to near Milwaukee, a distance of more than 900 miles. About 5 million people were in areas under a blizzard warning.

Snow created a few problems in Denver on Wednesday, with hour-long flight delays reported at the airport.

Heavy snow and whiteout conditions also closed interstates and caused driving problems in Utah, Colorado, Nebraska and Kansas on Wednesday. On Thursday, several states were reporting numerous traffic accidents, including one fatality in Nebraska.

In Utah, Washington County Sheriff's detective Nate Abbott says the woman and a man were driving when their car got stuck in rural Washington County Tuesday night during the storm that hit the Rocky Mountain region.

He says the pair started walking for help, but the woman couldn't go any further and sought shelter while the man continued on. Search and rescue teams later found her body.

South of the snowstorm, blowing dust led to near-zero visibilities in West Texas, which caused a major car wreck that killed one person.

In the South, AccuWeather was forecasting severe weather. States where the threat is the highest include Arkansas, Missouri, Louisiana, Mississippi and Alabama, the Storm Prediction Center reported.

"The greatest risk from the storms appears to be damaging wind gusts and flash and urban flooding," AccuWeather meteorologist Eddie Walker said. "However, there is a slight possibility that a few storms can be intense enough to produce a tornado."

Although the Plains and Midwest could do without the travel headaches, precipitation should be welcome.

More than 93% of the high Plains region and 54% of the Midwest are enduring drought conditions, according to the most recent U.S. Drought Monitor, a federal website that tracks drought.

Contributing: Ben Mutzabaugh, USA TODAY; the Associated Press; The Des Moines Register