This La Nina season is shaping up to be an early and wet one already, and after last week's rain, more is heading toward Northern California as soon as Friday.

The National Weather Service is making no promises — the forecast is currently "low to moderate confidence" — but the agency says that a low pressure system is moving down from Alaska and should be impacting the West Coast with rain by Friday, likely starting in the North Bay.

The storm system is being called an atmospheric river, and meteorologists say that parts of Northern California and the southern Oregon coast are the most likely to see heavy rainfall by the weekend.

"We've had systems that have characteristics of atmospheric rivers, but this one and potentially some after — it'll be an active pattern — will have the true qualities of an atmospheric river," says NWS meteorologist Joshua Wood, speaking to Newsweek.

As the Reno Gazette-Journal reports, heavy snow is possible in the Sierra, potentially hitting Donner Pass late in the weekend. But if the storm tracks further north, then the heaviest precipitation will hit western Nevada, with the Tahoe area still likely to see heavy winds and lower-elevation rain.

An Area Forecast Discussion posted by the NWS Monday suggests that the heaviest rainfall will be outside the Bay Area, with Del Norte County potentially seeing three inches from this atmosheric river. Mendocino and Lake counties have only a 30% chance of heavy rainfall.

Accuweather currently shows San Francisco staying dry Friday and Saturday, with light showers forecast only for Sunday. Sunny or partly sunny skies and mild to warm afternoon temperatures are predicted all this week.

Photo by Mark Tenn