The storm system, which rapidly intensified into a bomb cyclone on Tuesday, unleashed hurricane-force winds, heavy rainfall, and significant snowfall across parts of Washington state, Oregon and California, Xinhua news agency reported.

The United States National Weather Service (NWS) reported wind gusts of up to 158 km per hour along the Oregon coast and 124 km per hour at Mount Rainier in Washington state.

In Washington State, the storm claimed at least two lives and left about 600,000 homes without electricity at its peak. As of Friday evening, more than 260,000 customers in Washington State and Oregon, along with 92,000 in California, remain without power.

In Oregon, the atmospheric river has delivered intense rainfall, and some areas may receive 20 to 30 centimetres of rain. The NWS has issued flood watches for Oregon through Friday evening.

California also felt the brunt of the atmospheric river, with rainfall totals of 15 to 30 centimetres reported in some areas by Thursday. About a dozen minor landslides were reported in the state in just 24 hours.

Transportation across the region was severely disrupted. In Washington State, a train collided with a fallen tree in north of Seattle, though no injuries were reported among the 48 passengers.

The storm also brought significant snowfall to higher elevations. A blizzard warning was issued for much of the Cascade Range in Washington State. The northern Sierra Nevada and Oregon Cascades are also expected to receive between 30 and 61 centimetres of snow.

Climate scientists warned that this storm highlighted California's increasingly extreme weather patterns.

Daniel Swain, a University of California, Los Angeles (UCLA) climate scientist, described it as another example of the state's "hydroclimate whiplash" - sudden and dramatic shifts between dry and wet conditions that are expected to become more frequent as global temperatures rise.

The National Weather Service has urged residents in affected areas to stay indoors and avoid unnecessary travel. Emergency responders across the region are working to clear debris from roads and rescue individuals trapped by fallen trees or flooding.

The atmospheric river was expected to persist through Saturday morning, with the potential for another storm system to develop over the weekend.