Flash Flood and Wind Watch. Atmospheric River arrives Tuesday.

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The North Bay is headed for another dose of soaking rain, and this time a mix of subtropical air and cold from the north is expected to drop lots of rain across the region.  In fact, the system arriving Tuesday afternoon is shaping up to be another atmospheric river event. The Russian River may rise to flood stage by early Friday.

Flash Flood and High Wind Watches have been issued for Sonoma County and the rest of the Bay Area from Tuesday at 10PM, to Thursday at 10AM.

Tuesday’s satellite view shows the storm dropping down from the north, along with Atmospheric River moisture from near Hawaii streaming in from the southwest.

The cold front and subtropical moisture will converge by sometime Tuesday west of Northern California.  For us that means we could see a day and a half of moderate to heavy rain, starting late Tuesday afternoon.  Winds will also be high, up to 60 miles per hour as the low center approaches the coast on Wednesday.

Beginning Tuesday afternoon, the animation below shows the storm spreading heavy rain at times through late Wednesday.

There may be urban flooding by Wednesday morning, including small rivers and creeks topping their banks, and water on roads including Highway 101.  Small debris flows and rockslides are also possible.  The Wednesday morning and evening commutes will be slow and messy, so exercise caution.

The Russian and Napa Rivers are expected to rise quickly, and each may reach flood stage by late Thursday or early Friday.

The jet stream is forecast to push all of this atmospheric river moisture into California from the southwest (that Hawaiian moisture we mentioned pictured in green below) giving Central and Southern California lots of rain…and causing snow levels to rise in the Sierra.

The estimates of rain for the North Bay by Thursday range from 2 to more than 4 inches in the valleys, and 4 to as much as 8 inches in the coastal hills.  Here is the estimate from the Canadian model, which is one of the wetter forecasts. It shows almost three and a half inches by Thursday in Santa Rosa.

So get ready for lots more rain and messy driving from Tuesday afternoon through Wednesday evening.

Looking further ahead, after some weaker and cooler storms for the weekend, it looks like the West Coast may finally transition to a more tranquil, drier and slightly warmer weather pattern by the last week of February.

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