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A historically strong bomb cyclone killed at least one person and caused a massive power outage that could last days after hitting the Pacific Northwest and Canada’s British Columbia with destructive winds.

Now a new threat from the storm will emerge on Wednesday as the winds die down: Its combination with an atmospheric river will cause life-threatening flooding across parts of the West Coast that will continue for the rest of the week.

More than 500,000 homes and businesses were without power in Washington early Wednesday morning after hurricane winds destroyed the state’s energy infrastructure on Tuesday, according to PowerOutage.us. Nearly 100,000 customers were without power in British Columbia, BC Hydro reported on its website.

Hurricane-force winds of up to 75 miles per hour caused extensive damage in the western part of the state, knocking down numerous trees in addition to power lines. The Seattle area was especially hard hit. Puget Sound Energy, which serves the area, said more than 450,000 customers lost power due to a “massive outage” that could last “several days.”

‘It’s serious there. Trees are falling across the city, with several falling on homes,” the fire department in Bellevue, east of Seattle, warned on social media on Tuesday.

In Lynnwood, north of Seattle, a woman in her 50s was killed Tuesday shortly after 7 p.m. when a large tree fell on a homeless encampment, the South County Fire Department told CNN.

Southeast of Seattle, two people in Maple Valley were rescued and taken to a nearby hospital after a tree fell on their trailer. While one person was quickly freed, it took an hour to free the second, according to Puget Sound Fire.

On Tuesday night, a tree struck the home of Washington resident Rob Corcoran, and when it did, he told CNN it sounded like a plane landed on his roof.

“I didn’t even go outside because I was afraid I was going to get hit by flying debris,” Corcoran said. “I had no idea it was as bad as it is.”

An Amtrak train collided with a fallen tree north of Seattle in Stanwood on Tuesday evening, according to CNN affiliate KIRO. The incident left the train inoperable, although none of the 47 passengers on board were injured, KIRO reported. CNN contacted Amtrak for more information.

The storm rapidly intensified from Monday evening into Tuesday in a phenomenon called “bombogenesis” and was given meteorological status nickname of ‘bomb cyclone’.

Bomb cyclones are formidable, dumping heavy snow and strong winds in winter.

It tied with the most intense on record for its location, a storm so strong it only occurs “about once every ten years,” the National Weather Service in Medford, Oregon, said Tuesday. It more than doubled the criteria needed to be classified as a bomb cyclone from Monday evening to Tuesday evening.

The powerful cyclone unleashed widespread wind gusts of 60 to nearly 80 mph across western Washington, while even stronger winds of up to 100 mph roared just off the coast, according to the National Weather Service in Seattle.

Wind gusts of up to 60 miles per hour hit western Oregon and gusts of up to 80 miles per hour hit Northern California.

Winds will remain strong until at least early Wednesday before gradually decreasing to gusty, but less damaging, levels. But the weather threat in the region is far from over.

Rain drenching Northern California and parts of the Pacific Northwest early Wednesday will intensify through the day as an atmospheric river strengthens and finally peaks in intensity on Thursday.

An atmospheric river is a firehose of moisture that, when tapped into by a storm such as the Bomb Cyclone, often inundates those in its path with heavy rain, sometimes lasting for days.

That’s what will happen this week, so according to the Weather Prediction Center, there is a Level 3 of 4 risk of flooding rains for parts of Northern California on Wednesday. That risk level rises to a rare level 4 of 4 high risk on Thursday.

“Flash flooding will pose an increasing risk, with the potential for life-threatening conditions,” the weather service in Eureka, California warned late Tuesday.

Parts of Northwestern California could see 6 inches or more of rain in 48 hours. More than a month of rain is expected in the northern San Francisco Bay area, especially north of the Golden Gate Bridge, the weather service there said. Rainfall of this magnitude is expected to cause significant urban flooding, road debris flows and river flooding.

Heavy rain will continue through Friday in parts of Northern California as the drenching weather gets another jolt of atmospheric energy from another storm to keep it churning.

Another bomb cyclone could develop just off the west coast on Friday and quickly strengthen. This new storm will likely be weaker than the first, but will still fuel rain threats across the region and could also usher in another round of damaging winds.

CNN’s Isaac Yee, Sara Smart and Mike Madrigal contributed to this report.