Atmospheric river threatening West Coast with floods, heavy rain

An atmospheric river will continue to impact the West Coast over the next 24 hours.

A record amount of moisture is hitting the Pacific Northwest as the powerful system continues to bring heavy rainfall to the region.

Up to 8 inches of rain has already fallen in parts of Washington, with several cities reporting daily record rainfall on Monday, according to the National Weather Service. The excess runoff is now forcing many lowland rivers beyond their banks.

Atmospheric rivers are essentially rivers in the sky that collect moisture from tropical areas and redistribute the water to other latitudes.

The weather phenomenon occurs frequently around the globe, but they cause 80% of flood damage at an average estimated cost of $1.1 billion annually on the West Coast of the United States, according to researchers at Phys.org.

The current plume of moisture in the Pacific Northwest will continue into Washington on Tuesday morning and then will move into Oregon in the afternoon and evening, bringing an additional 5 to 8 inches of rain, forecasts show.

The National Weather Service has issued flood alerts for Washington, Oregon, and Idaho for river and stream flooding, as well as Northern California for heavy rainfall and snowmelt. Ponding of water on roadways, isolated minor flooding in low-lying areas, and isolated rock falls and mudslides will be possible.

Portions of Montana are under an avalanche warning until 7 p.m. local time for new snow, blowing snow and rain on snow, creating dangerous avalanche conditions.

By Wednesday morning and afternoon, some of the rain is expected to move into Northern California and the San Francisco Bay area. Major flooding is not expected in California.

More storms are expected to hit the West Coast on Thursday and then again on Saturday, with more rain at the coast and lower elevations.

With the storms later in the week, the air mass will be colder, so the snow will fall in lower elevations, possibly covering I-90 and I-80 in snow, which could make commutes dangerous.