Atmospheric River Predicted to Lash US West Coast

The sodden West Coast has been told to brace for yet more wet weather as forecasters said that an "atmospheric river" is on the way to batter the area.

The weather phenomenon, described by the National Oceanic and Atmospheric Administration (NOAA) as "like rivers in the sky," describes a strip in the atmosphere that transports water vapor outside of the tropics. Large atmospheric rivers can carry up to 15 times "the average flow of water at the mouth of the Mississippi River."

Experts have said Americans are likely to see radically different weather this year compared to 2023, as an El Niño weather pattern (when warmer waters are shifted east) looks set to lead to potentially volatile conditions.

Residents living along the West Coast have been told they could see flooding, landslides, and coastal erosion from fierce waves, while above-normal levels of rain lash down.

This week's soggy forecast comes as much of California has suffered from unusually wet conditions. A fierce winter storm sparked flash flooding in San Diego; cars were washed away on Monday after a record-breaking amount of rain prompted authorities to declare a state of emergency.

An atmospheric river that developed on Friday has already impacted the state's reservoirs; one rose by 5 feet as rain swelled the water levels. Although some rain was welcomed as a result of the state's recent suffering during a prolonged drought, the amount of rainfall has prompted fears of flooding, mudslides, and sewage water spillovers.

The National Weather Service (NWS) shared details of the atmospheric river on Monday, and said it was expected to hit the West Coast next week from January 30 through February 5. The government agency shared an alert on the social-media site X (formerly Twitter), which was viewed almost 100,000 times in just one day.

"Confidence is growing of an impactful atmospheric river event moving southward along the West Coast January 30th through February 3rd," NWS said. "Following this event, the pattern will remain favorable for above-normal precipitation through February 5th.

"There is a 60 to 80 percent chance of above-normal precipitation across much of the West Coast [...] During the atmospheric river event, there is a moderate risk of heavy precipitation across most of California and coastal portions of the Pacific Northwest [...] with a high risk across California [...] that can lead to localized flooding and landslides."

Snow may even be seen on higher ground in the northern Sierra Nevada and Klamath Range, the agency added.

"Hazardous, onshore high winds are likely to impact the West Coast as well [...] particularly the Pacific Northwest southward through much of California, which could lead to coastal erosion from persistently high waves," the NWS said.

Residents were urged to monitor their local weather forecasts carefully.