How bad will California’s monster storm get? Here’s what you need to know

A series of storms that some forecasters say could be the most severe in a decade is beginning to barrel down on Northern California.

The epic system — known as an atmospheric river — could dump so much rain and snow that some ski runs and roads will be declared off-limits, with forecasters warning of significant flooding, mudslides and avalanches in the Sierra Nevada.

Up to 12 inches of rain is expected to fall on areas below 8,500 feet beginning Saturday morning, and up to 7 feet of snow could bury higher elevations, according to the National Weather Service. Forecasters said the storm was packing the same wallop as one that hit Northern California in 2005, causing $300 million in damage.

This weekend’s system could bring 36 consecutive hours of heavy rain from Mammoth Mountain to Susanville, in Lassen County. Though that is good news for California, which is entering its sixth year of drought, the coming rain could melt already standing snow — feeding watersheds swollen from storms earlier this week, forecasters said. 

“It’s going to be a busy weekend,â€� said Edan Weishahn, a meteorologist with the National Weather Service in Reno, sighing. 

Here’s a quick breakdown of what you need to know.

So what is the timeline for the storm systems in Northern California?

There will be rain and snow at least through Wednesday. The worst of it will be Sunday, but the flood risks continue through mid-week. Here’s a weather service graphic:

Why is flooding such a concern?

Big storms like this — especially ones that come one after another — regularly bring flooding along rivers and streams. It’s caused both by swelling from rain and the melting of snow from higher elevations.

A wide swath of Northern California is under flooding warning:

How can I prepare for flooding and potential power outages?

Here are some tips:

So what do the snow levels look like for the next few days?

Here are some maps from the National Weather Service:

How about rain totals?

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