A storm off the coast of the US north-west and western Canada is pummelling the region – bringing high winds, flooding and snow to over seven million residents living in states along the Pacific Ocean.

The storm has caused widespread power outages for hundreds of thousands of Americans, and its strong winds have downed trees.

At least one person – a woman near Seattle – has died.

The “bomb cyclone” – as forecasters call it – has been caused by air pressure quickly dropping off the coast, which has rapidly intensified the weather system.

Winds, rain and snow expected through the week

The effects of the storm were seen on Wednesday morning, with fallen trees damaging homes and blocking roadways in Washington state.

A woman died when a tree fell on a homeless encampment in Lynwood, north of Seattle, Washington, according to a social media post from South County Fire Department.

High winds are leading to power cuts. On Wednesday morning, more than 600,000 homes in Washington were without power, according to poweroutage.us. Around 15,000 customers were experiencing outages in California.

Several schools in Washington are expected to close or face disruption.

“It’s severe out there. Trees are coming down all over the city, with multiple falling onto homes,” Washington’s Bellevue Fire Department wrote in a social media post. “If you are able, head to the lowest floor you can and stay away from windows. Do not go outside if you can avoid it.”

In northern California, the US Weather Prediction Center (WPC) said there was a high risk of excessive rainfall and warned of flash flooding and mudslides. The San Francisco Bay is expected to see up to 8in (20cm) of rain.

The storm has also stretched up to Canada, where wind is the primary concern and gusts of up to 100mph (160km/h) have been reported off the coast of Vancouver Island. Around 140,000 customers were without power in British Columbia, according to the British Columbia Hydro and Power Authority.

BBC Weather presenter Stav Danaos said damaging gusts would continue to ease on Wednesday, although conditions are expected to remain blustery along the Pacific coast from San Francisco up to Vancouver Island.

And incessant heavy rain is expected throughout Thursday and Friday along much of the coast, as a renewed “atmospheric river” of moisture from the Pacific is driven onshore.

Beyond wind, rain and snow, the storm could also bring flash flooding, rock slides and debris flows, as well as heavy mountain snow, in areas of high elevation. The storm is expected to create blizzard conditions through the Cascade Range of mountains, which runs through both the US and Canada.

The heavy, wet snow that has fallen on the Cascades and North Rockies will start to thaw towards the end of the week as milder air is ushered in.

This snow melt, combined with further heavy rain, is likely to lead to severe flooding in places from Northern California to Oregon, with a significant risk of landslides as the week ends.

What is a bomb cyclone?

Bomb cyclone is a term given by meteorologists to a storm that appears to intensify rapidly, with its central air pressure dropping to at least 24 millibars in 24 hours.

They are referred to as bomb cyclones due to the explosive power of these storms caused by the rapid fall in pressure.

The storm brings with it an array of weather, ranging from blizzards to severe thunderstorms to heavy precipitation.

These weather events are not unusual for this time of year.

Similar so-called atmospheric river events – when small regions of moisture travel outside tropical regions – have occurred throughout North America over the last few weeks.

But the conditions of an atmospheric river combined with a bomb cyclone can create a major weather event. (BBC)

•A low pressure storm system known as a “bomb cyclone” forms off the coast of the U.S. Pacific Northwest and western Canada in a composite satellite image November 19, 2024.

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