San Francisco Bay Area weather: atmospheric river bringing heavy rain

An intense storm is headed to the Bay Area on Wednesday after near-record high temps in the 70s kicked off the week. 

Monday has seen temperatures up to 15 degrees higher than normal and Tuesday will see increasing clouds, according to the National Weather Service. 

But beginning from Wednesday through Thursday, meteorologists predict a potent storm with plenty of moisture will throw heavy rain and gusty winds at the West Coast. Light rain is expected on Friday. 

As of now, the rain will be heaviest in the late afternoon on Wednesday, affecting the evening community and into the Thursday morning commute. 

The upcoming storm will trigger an atmospheric river, bringing rain heavy enough to cause flooding, mudslides and major travel disruptions.

This new storm will deliver a narrow zone of intense rain from well out over the Pacific and toward coastal areas of California. The fire hose effect of rain will shift southward from Northern California on Wednesday to Southern California on Thursday.

The NWS anticipates between 2 and 4 inches of rain in the Bay Area over those two days. 

Drenching rain will reach Los Angeles and San Diego on Thursday when the heaviest downpours are likely.

Some areas, especially along the west- and southwest-facing mountainsides in Santa Barbara and Ventura counties, will get higher totals locally, perhaps exceeding four inches. 

If the storm picks up speed, there will be less rain.

If the storm stalls, there will be more rain.

Regional flash flooding problems are likely, with incidents of debris flows, rockslides and washouts as well.

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Small streams will rise rapidly, and some of the rivers in the northern and central parts of the state may flood.

Some of those areas include the usual suspects in the North Bay, such as Guernevill because of the rising Russian River, the San Lorenzo River in the Santa Cruz mountains and the San Francisquito Creek on the Peninsula.

Much of the Sierra Nevada might see significant wet snowfall with freezing levels starting above pass level on Wednesday, falling to pass level on Thursday, then dropping below pass level by Friday.

The current Sierra Nevada snowpack is running well below average pace for late January. In the northern Sierra, the season-to-date tally is 65%, while in the southern Sierra, the amount is 36%. The storm from Wednesday to Friday should provide a boost.

Even the Southern California mountains will get snow at the end of the week.

Another round of storminess with low-elevation rain and mountain snow is expected to hit from Sunday to next Monday.