A highly-anomalous atmospheric river is expected to set up and direct its moisture into Southern California Wednesday into Thursday, leading to heavy rain and the risk for flooding and landslides in the burn scar areas to this portion of the state while the Sierra Nevada experiences heavy snow. The combination of this atmospheric river originating from the central Pacific and multiple low pressures under a new trough will allow for widespread valley rain and mountain snow across the West Coast and eventually the intermountain West. The European model image below shows that atmospheric river based on normalized anomalies, highlighting where the greatest moisture will be.

This plume of moisture directed by an incoming trough will aid in several days of rain and snow beginning Tuesday and lasting through Thursday night for California while the Northwest experiences a more prolonged event of precipitation. This is a big deal for the Golden State. It’s been very dry this winter until now, where these storm events have become more frequent this March. The Sierra Nevada is still running below average in terms of snow water content. It’s currently at only 40% of normal, but if another two to three substantial storms move in, that could help alleviate the situation a lot.

There is also a drought that continues to plague portions of California. Most of the state is currently experiencing at least abnormally dry conditions and nearly half is in a drought. The worst drought conditions are located in Southern California, which coincides with the quieter snow track this winter season.

Based on the current forecast, up to three to four inches of rain may fall in the lower elevations of Southern California and about an inch to the Central Valley. In the Sierra Nevada, over five inches of snow will fall in the highest peaks. Light snow may also fall in the San Gabriel Mountains.

We’ll have more details and timing on this story as the event approaches.


Jackson is Head of Content and Social Media at WeatherOptics. He is currently a student at the University of Miami, studying Meteorology and Broadcast Journalism. Dill produces forecast articles for the website and helps to manage the content schedule. He has also led the growth of WeatherOptics’ social media accounts, working to keep them aligned with the company’s evolving vision.

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