It’s going to get cold and rainy again in Sonoma County. Here’s when

Overnight temperatures are predicted to drop to frigid levels both before and after the rainy and snowy storms land later this week in the North Bay, according to the National Weather Service.

Temperatures late Monday into Tuesday went down to the mid- to upper-30s, with the Napa County Airport recording a low of 34 degrees and Charles M. Schulz Sonoma County Airport seeing 39 degrees.

The lows will likely be comparable, though slightly warmer, on Tuesday, said Sarah McCorkle, a meteorologist with the weather service’s Monterey office.

“It will be another chilly night,” McCorkle said.

A frost advisory will be in effect from 2 a.m. to 9 a.m. Wednesday for most of the North Bay, not including the immediate coast, due to the temperatures dropping about 5 to 8 degrees below normal. A similar advisory was in effect Monday night to 9 a.m. Tuesday.

The cooler temps were triggered by a small cold front that swept through Monday that dropped trace amounts of rain, such as about 1/100 of an inch in Santa Rosa. It was small, but “enough to bring in some cold air,” McCorkle said.

The next round of rain will be more noticeable.

Widespread lighter rains will start Thursday and evolve into scattered and potentially heavier storms by Friday, McCorkle said, dropping up to 2 inches of rain in Sonoma County’s coastal mountains and close to 1 to 1 1/2 inches in the North Bay valleys.

The area around Lake Berryessa, which has waters rising close to the top of the circular spillway known as the “Glory Hole,” will get around 1 1/4 inches. It’s unclear whether the rainfall will be enough to push water over its edge.

“The most likely period we're expecting more moderate to heavy rain will be late Friday and Saturday. It looks like there could be some more thunderstorm potential during that time frame,” she said.

Thunderstorm chances will peak at 15% during that window, and winds will increase to 25 mph, with gusts reaching 40 mph on the coast and in the coastal mountains.

“It'll be kind of a mix all those days,” she added, referring to the intensity of the rain and winds.

Because the showers are spread out over three days, the weather service is not expecting many flood-related hazards. Nuisance flooding on roads is most likely to occur, according to the weather service’s area forecast discussion.

“This weekend, simply put, just won't be a fun time to be outside with it being wet, windy and cold,” the discussion said.

For the first time this year, snow may be visible atop the Mayacamas Mountains.

Snow will be possible above 2,500 feet , McCorkle said. Up to 3 inches of snow could fall in areas of higher elevation.

After the storms fade Saturday afternoon, temperatures will again decrease — possibly reaching down to the low-30s overnight Saturday and Sunday, McCorkle said.

The North Bay valleys will then have “cold mornings with freezing temps possible” Sunday night into Monday morning, according to the forecast discussion.

“These cold temperatures,” the discussion said, “pose a hazard to unsheltered and marginally sheltered populations.”

You can reach Staff Writer Madison Smalstig at madison.smalstig@pressdemocrat.com. On X (Twitter) @madi.smals.