Rain on the way: Atmospheric river to drench Bay Area starting Friday

Rain is returning this week to the Bay Area – and forecasters are expecting a "potentially major storm system."

The weather is expected to shift Friday with rainfall continuing through next Thursday, according to the National Weather Service. 

The greatest impact is expected in the North Bay, the agency said. 

Gov. Gavin Newsom's office said the state is preparing emergency resources due to the atmospheric river arriving this weekend in Northern California. 

How much rain will there be in the Bay Area?

What we know:

"National Weather Service Sacramento is forecasting a moderate to strong atmospheric river to begin Friday and continue into next week," the governor's office said. "Prolonged periods of rain and mountain snow are expected, with the potential for flash flooding and rising creeks, rivers, and streams."

State officials warned that the atmospheric river could bring the risk of power outages, flooding and debris on roads. 

The weather service said "more significant" rainfall is possible starting Sunday, into next week.

Over the next seven days, the NWS is estimating several inches throughout much of the Bay Area. Parts of the North Bay and San Francisco may see up to 6 inches.

The weather agency shared a map on social media with potential rain totals through next Thursday.

San Francisco's Department of Emergency Management reminded residents Thursday to plan ahead in case of wet roads.

When will the rain end?

Big picture view:

The National Weather Service shared the disclaimer that the exact timing and intensity of this storm is still uncertain, but rain projections show wet weather through next Thursday, Feb. 6.

The new year has been largely rain-free in the Bay Area, with "abnormally dry" drought conditions, we reported earlier this month.

The Bay Area's last significant storm was just before Thanksgiving. San Francisco, along with cities in Sonoma County saw major flooding.

What is an atmospheric river?

Atmospheric rivers are long bands of water vapor that move through the sky. They can be 250 miles wide and 1,000 miles in length. They are the largest rivers of fresh water on the planet and they're responsible for more than half of California's annual precipitation. 

Powerful atmospheric rivers can create extreme rainfall and floods, which can also trigger mudslides and cause "catastrophic damage to life and property," according to the National Oceanic Atmospheric Administration. 

The federal government estimates that atmospheric rivers have been associated with $1 billion of damage every year, with 80% of the flood damage in California. 

The Source: National Weather Service, Department of Emergency Management, previous KTVU weather reporting

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