By Holly Yan and Judson Jones, CNN
(CNN) -- You know it's bad when forecasters urge people to avoid travel before Thanksgiving.
Just in time for the busiest travel days of the year, 21 million people are now under some kind of winter weather advisory.
"A historically strong storm in the West could bring hurricane-force wind gusts, while another powerful storm spreads snow and wind from the Rockies to the Great Lakes," CNN meteorologist Dave Hennen said Tuesday morning.
"Impacts from the storms will spread over 2,000 miles from California to Michigan today."
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 to expect across the country:
The West Coast: You might want to stay in
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 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.
Parts of the Pacific Northwest could face a bomb cyclone, a type of rapidly strengthening storm.
READ MORE: What's a bomb cyclone?
Even in Southern California, the mountains outside Los Angeles could get a foot of snow, Hennen said.
Other parts of California can expect a soggy Thanksgiving week, with 11 million people under flash flood watches.
Rockies and Plains: Watch out for blizzard conditions
A winter storm pounding the Rockies with blizzard conditions will head to the Plains and Upper Midwest by the end of this week.
In Wyoming, over 200 miles of Interstate 80 were closed Tuesday morning, the Wyoming Department of Transportation said.
Many drivers across the state are dealing with black ice, blowing snow and reduced visibility.
Denver International Airport reported more than 470 flights cancellations Tuesday due to the weather.
More than 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 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.
The-CNN-Wire
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