Rain, colder temps on the way to Sonoma County

Forecasters are predicting below freezing nighttime temps in the North Bay through Friday.

The cool down will take place just ahead of an atmospheric river that promises to drop as much as 5 inches of rain on parts of Sonoma County and the rest of the Bay Area this weekend.

Rain has been in much of this area’s weather forecast since the beginning of the week, but it has all been rather light.

Forecasters were again predicting trace amounts of precipitation in the region on Wednesday, according to National Weather Service meteorologist Drew Peterson.

Drizzling and light showers that began Wednesday evening would continue overnight into Thursday, he added.

A few hundredths of an inch are expected for some areas of Sonoma County and less than a tenth of an inch is forecast for Napa and Marin counties.

By Thursday night, temperatures in Sonoma County are expected to drop to around 30 degrees. The same is expected to happen on Friday night, said weather service meteorologist Roger Gass.

Some of the area’s coldest pockets will be in Petaluma, Sebastopol, Graton, Rohnert Park and Santa Rosa, while Sonoma could dip down to 28 degrees on Thursday and Friday nights, Gass said.

A freeze watch has been issued for parts of Humboldt, Mendocino and Lake counties on Thursday night into Friday morning, and the National Weather Service advises residents to consider moving outdoor pets inside and protecting plants.

Once the freezing temperatures leave, an incoming atmospheric river will target the Bay Area this weekend into early next week, Peterson said.

“This looks to be a pretty decent rainstorm, more typical of regular winter storm situations,” Gass said.

The storm will begin late Saturday night in Sonoma County and will spread out across the entire Bay Area Sunday and Monday, Peterson said.

Two to 3 inches of precipitation are expected for Sonoma County cities. Coastal ranges could see 2 to 5 inches of rain.

The storm is expected to clear out by the end of Tuesday, Gass said.

An atmospheric river in late October brought widespread flooding, power outages and traffic problems across the North Bay and dumped 7.83 inches of rain on Santa Rosa on Oct. 24, the highest 24-hour rainfall ever recorded in the city.

Typically, early December sees an average of 6.76 inches, according to a 30-year average recorded at the Charles M. Schulz-Sonoma County Airport. Last year, amid a drought, December only saw a meager 3.02 inches at the airport.

The U.S. Drought Monitor shows most of Northern California is in an “extreme drought” despite heavy rainfall in October.

“One storm is not going to make us go from extreme drought into normal,” Peterson said. “We’ve still got quite a deficit.”

Track the storm using the real-time radar map below:

Staff Writer Kathleen Coates contributed to this story.You can reach Staff Writer Alana Minkler at 707-526-8511 or alana.minkler@pressdemocrat.com. On Twitter @alana_minkler.