Are Incoming Atmospheric Rivers Getting An El Niño Boost?

While it’s tank top weather today, by Wednesday night you’re going to want to grab your galoshes, as the first of two atmospheric rivers is expected to arrive in the area.

The storms are standard for this time of year, but a warm patch of water off the coast, likely associated with El Niño, is a must watch.

The forecast

With the first storm, Southern California is likely to see one to three inches of rain in our urban areas, and as much as five inches in our foothills and mountains. Strong wind gusts of up to 40 miles per hour could potentially impact LAX.

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Snow levels will drop to between 3,000 and 4,000 feet by Thursday night, meaning there’s about a 20% chance that an inch or two of snow will fall on the Grapevine and Cajon Pass.

Things should start to dry out by Friday, but then quickly pick right back up with the second storm on Sunday. That atmospheric river will stick around until Tuesday, bringing long periods of steady rain.

The storm’s still a bit too far out to forecast accurately, but two to four inches of rain is possible, as is heavy flooding. We’ll have a better idea of what to expect in the coming days.

Our nearby mountains could see several feet of snow above 7,000 feet, while more than four feet could fall in places like Yosemite.

Atmospheric rivers are responsible for bringing substantial precipitation to California.

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National Oceanic and Atmospheric Administration

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https://www.noaa.gov/stories/what-are-atmospheric-rivers

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The El Niño power up

Speaking of forecasts, the models aren’t quite there yet when it comes to accurately incorporating an anomalously warm area of sea water stretching a few hundred miles out into the Pacific.

“That signature of warm surface water is characteristic of strong El Niños,” said Marty Ralph, director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography.

The blob is about six to eight degrees above normal and can be found from Baja all the way up to Point Conception.

Ralph says that it’s strengthening the incoming atmospheric rivers and raising the risk of local flooding potential as it adds heat and water to the atmosphere. Though, it’s difficult to predict exactly what’s going to happen.

“We’ve concluded that conditions are ripe for … one to two hour long periods of exceptionally heavy rainfall within a longer period of moderate rainfall,” said Ralph.

The same warm water conditions were present off of the coast of San Diego during last week's rains, which caused extensive flooding.