Flash flood watch for much of southeast Wisconsin beginning at 3pm

Below-freezing temperatures set to sweep the country

People walk along West 59th Street near Central Park bundled against the cold in advance of a winter storm on January 2, 2014 in New York. The northeastern United States prepared Thursday for snow, high winds and frigid temperatures, as a gust of wintry weather bore down on New England and surrounding states, cancelling flights. Temperatures in New York were expected to drop to 10 degrees Fahrenheit (minus 12 degrees Celsius) with a windchill factor of minus nine degrees Fahrenheit, according to national weather forecasts. AFP PHOTO/Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images)

The cold is taking hold of the US weather pattern for the next week. Over the next seven days, 80% of the country will at some point see temperatures below freezing.

More than half the continental United States will have below-average temperatures Friday. Temperatures will be 20 to 30 degrees below average in locations stretching from the Montana to South Texas.

Dangerous wind chills could yield temperatures as low as 40 degrees below zero in the Northern Plains on Friday.

Snow contributed to a 30-car pileup on Interstate 96 in Fowlerville, Michigan, on Thursday. Police reported two deaths.

‘Domino effect’

In Ohio, snowy conditions led to a more than 50-vehicle pileup on I-90 in Lake County, officials there said. The Lake County Sheriff’s Office said multiple people were trapped in their cars.

Authorities said at least 19 people were injured, including five seriously, in the crash between Route 44 and Vrooman Road in the area of Painesville, CNN affiliate WJW reported.

Greg Carmichael, a passenger on a Greyhound bus involved in the pileup, told WJW he was bound for Buffalo when a semi hit the bus from behind about an hour into the ride.

“It just was a domino effect, everybody crashed,” he said.

Carmichael added: “There was some guy that was literally buried under his truck.”

Several passengers on the bus were among those treated for serious injuries, WJW reported.

In Portland, Oregon, state police said icy conditions contributed to a crash that killed one person Thursday morning on Highway 99 in Benton County, CNN affiliate KOIN reported.

Cold air will push into the Northeast and Southeast on Friday, with subfreezing low temperatures reaching the Gulf Coast by Saturday morning.

Another, even colder air mass is forecast to enter the Midwest and Northeast late next week.

According to meteorologist Ryan Maue, the upper-level atmosphere configuration looks very similar in scale and magnitude to the January 2014 “polar vortex” that left the country in below-average temperatures for days. Luckily, next week’s cold spell will last only a few days.

Lake-effect snow started along the southern and eastern shores of the Great Lakes on Thursday and is expected to last until early Saturday. More than 5 million people are living in areas covered by a lake-effect snow warning, watch or advisory.

The heaviest snow bands could bring over a foot of accumulation in the Upper Peninsula of Michigan and nearing 2 feet in parts of upstate New York.

A strong storm entering the Northwest will bring more snow on Friday, not only to the mountains but to lower elevations as well.

About 10 million people are under winter storm warnings and winter weather advisories in the West.

Snow will spread throughout the region, with feet of accumulation expected in the mountains. Portland, Oregon, and Seattle will get a couple of inches.

After exiting the West, this system will leave a swath of snow as it passes over the Northern Plains and southern Great Lakes this weekend.

CNN’s Azadeh Ansari, Jackie Castillo, Amanda Jackson, Rashard Rose, Mayra Cuevas and Darran Simon contributed to this report.