PORTLAND — Northern California and southern Oregon residents are bracing for a weather “bomb cyclone” that’s expected at one of the busiest travel times of the year.

The storm expected Tuesday into Wednesday could be like nothing seen in the area in the past 20 years, with wind gusts of up to 75 mph in some locations and breaking waves of 35 feet or more.

“This is a significant storm system that will be coming in,” said Tom Wright of the National Weather Service’s Medford office. “Probably the bigger and more dangerous part of this whole thing is the windstorm we see coming.”

Residents in southwest Oregon should stay home and expect downed trees and power lines, authorities said.

Mountain passes in northern California and southern Oregon, such as Siskiyou Summit, were already getting heavy snow Tuesday, and high winds could create dangerous whiteout conditions on Interstate 5 during the Thanksgiving travel period, authorities said.

Mount Shasta City, California, could get up to 2 feet of snow and snow accumulations were also expected at lower elevations along Interstate 5 from northern California as far north as Medford, Oregon. Eugene, Corvallis and even Salem could see some sticking snow overnight Tuesday, according to the National Weather Service forecasts, but snow in Portland looked less likely Tuesday after initial predictions that the metro area could see a dusting.

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Wind gusts could top 75 mph (120 kmh) in Gold Beach, Oregon and 72 mph (115 kmh) in Brookings, Oregon, Wright said.

Cold temperatures arriving on Wednesday, after the storm passes, could create icy road conditions as well.

A “bomb cyclone” forms when air pressure drops by 24 millibars or more in a 24-hour period. This storm’s air pressure has dropped even more quickly than that, making it extremely dangerous, said Wright, with the National Weather Service.

Heavy rain is also expected along the Oregon coast but not enough to cause any flooding, he said.