Strong atmospheric river event brings flooding, possible mudslides to Northern California | CBS 42 Weather


An anomalously strong non-tropical cyclone has formed in the Northeast Pacific Ocean, bringing with it a very strong atmospheric river event into Northern California. An “atmospheric river” is simply an elongated stream of deep moisture that follows a storm system, which is typically how the US West Coast the vast majority of its annual rainfall in a given year.

An “atmospheric river” is simply an elongated stream of deep moisture that follows a storm system, which is how the US West Coast receives up to 90% of its annual rainfall in a given year. What sets this system apart from other events is just how strong the storm producing it is…

An extremely deep upper-level trough is what has caused this storm and subsequent atmospheric river to form, and it is one of the strongest storms ever recorded in the region…

The latest estimated minimum central pressure is 942.5 millibars…that’s comparable to a Category 3 hurricane. While this storm is slightly different than a Category 3 hurricane (different formation mechanisms, larger pressure gradient, etc.), it does help give some perspective of the caliber storm the West Coast is seeing.

With this storm and accompanying atmospheric river comes an elevated risk of flash flooding in Northern California, which has already started developing as of this Sunday afternoon. Many places the San Francisco Bay area to Sacramento and Reno, NV has already received 2 to 4″ of rainfall. Flash Flood Warnings are currently in effect for the mountainous area of NE California until early tomorrow morning.

Burn scar areas left behind by this year’s wildfires across California are at particularly high risk of flash flooding and mudslides, because of much looser soils from the loss in vegetation over the area…

Another interesting fact about this storm system: This will be the same storm system that brings our expected risk of severe storms Wednesday and into Thursday here in Central Alabama. The upper-level trough will continue downstream towards the Deep South over the next few days, and the same piece of energy will help fuel thunderstorms in our area Wednesday night, despite the storm itself not being quite as strong as it is now.

This is something we’ll be tracking as it develops. Be sure to stay up-to-date with our Central AL Forecast right here on, and by downloading the free CBS 42 News app on the App Store!

That’s all for now!  Be sure to follow the CBS 42 Storm Team on:

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