CNN  — 

Two powerful storms are set to bring big trouble for millions of Thanksgiving travelers.

The heavy snowfall that grounded hundreds of flights in Denver could soon do the same at the Minneapolis-St. Paul airport in Minnesota and dump several feet of snow on the Midwest.

All while another storm will hit the West Coast with hurricane-force winds and rainfall and the California and Nevada mountains with heavy snow, promising more travel disruptions on the busiest travel days of the year.

About 21 million people from the West Coast to the Great Lakes are under some kind of winter weather advisory. In Southern California and Arizona, 17 million are under flash-flood watches.

Track weather and travel forecasts here

Over the next few days, fierce winds from New Mexico to New York could cause power outages and even ground the famous balloons in the Macy’s Thanksgiving Day Parade.

Here’s what else to expect across the country:

The West Coast: A soggy, windy and snowy week

A dangerous storm is heading toward southwest Oregon and northwest California, the National Weather Service Weather Prediction Center said.

“Avoid travel on Tuesday & Wednesday if possible,” forecasters tweeted.

Southwest Oregon and northern California could face wind gusts up to 70 to 80 mph. To put that in perspective, a storm becomes a hurricane when sustained winds reach 74 mph.

But winds will not be the only concern. Forecasters say a a bomb cyclone, a type of rapidly strengthening storm, will bring snowfall to the Northwest and even to the mountains outside Los Angeles.

READ MORE: What’s a bomb cyclone?

Residents along the coast of California are bracing for more than a soggy Thanksgiving week. Some areas could see high waves, and heavy rainfall could cause flooding from San Diego to Los Angeles.

Rockies and Plains: Watch out for blizzard conditions

A snow storm pounding the Rockies with blizzard conditions was starting to spread into the Plains and Upper Midwest.

More than 200 miles of Interstate 80 have been closed for nearly 24 hours due to the heavy snow, the Wyoming Department of Transportation said.

A major snowstorm hit the Denver metro area this week.

Many drivers across the state and in neighboring Nebraska are dealing with black ice, blowing snow and reduced visibility.

“We been advising people to stay off the road,” said Nebraska State Patrol media director Cody Thomas.

Denver International Airport reported more than 480 flights cancellations Tuesday due to the weather.

About 1,100 passengers had to spend Monday night at the airport, spokeswoman Alex Renteria told CNN. Airport staff handed out blankets, baby formula and diapers, and restaurants stayed open longer than usual, she said.

Denver residents faced snow-packed roads and flight delays Monday and Tuesday.

Denver police reported multiple crashes and urged residents to stay inside.

“Please don’t drive if you don’t have to,” the police department tweeted.

Pre-winter weather has dumped 32 inches of snow on Boulder, Colorado. But it could get another 10 to 12 inches this week, CNN meteorologist Chad Myers said.

“We will even have some blizzard conditions across parts of Nebraska, Kansas and Colorado,” Myers said. “It’s going to be a mess.”

Eastern US: Beware rain and strong wind

Travel will get off to a slow start early Wednesday through the Deep South and into the Ohio River Valley.

Rain and low visibility will be the main hindrance, and both will push east Wednesday afternoon.

From Atlanta to New York, storms could interrupt air travel on Thanksgiving eve.

In the Northeast, travel delays are expected, as rain and strong wind linger from midday through the evening.

CNN’s Amanda Watts, Nicole Chavez and Artemis Moshtaghian contributed to this report.