September showers headed for Bay Area

A storm expected to arrive in the Bay Area as soon as Saturday night could dump enough rain on the region to temporarily tamp down the likelihood of wildfires, according to meteorologists with the National Weather Service.

In Sonoma County, meteorologists are predicting up to an inch and a half of rain in the wettest locations, which are the high-elevation areas.

About an inch of rain is predicted for lower-elevation spots like Petaluma, Santa Rosa and Sonoma.

But forecasters cautioned that the predicted amounts could change over the coming days as the storm draws closer.

The bulk of the precipitation is expected Sunday, but showers could continue through Tuesday, weather service meteorologist Roger Gass said.

“It’s looking to be a pretty decent rainfall event,” Gass said.

On the heels of a heat wave that broke an all-time temperature record in Santa Rosa at 115 degrees last week, the incoming moisture “could suppress fire concerns for a few days, or even a few weeks,” Gass added.

“Any rainfall is beneficial heading into what normally is the peak of our fire season,“ he said.

By the weekend, temperatures are expected to drop to unseasonably cool levels, according to the weather service.

For Santa Rosa, the predicted highs are 79 degrees Friday, 75 on Saturday, 63 on Sunday and 70 on Monday.

The average high temperature for the city in September is 76 degrees, weather service data shows.

The predicted rain is coming from a “pretty potent” upper-level low-pressure system dropping down from the Gulf of Alaska, Gass said.

Such storms at this time of year often move inland before they make it as far south as the Northern California coast, and that setup can result in offshore winds for the Bay Area. But meteorologists say this system is on track to line up with the coastal Bay Area and even the Central Coast.

It’s not unusual for Sonoma County to see September rain. In Santa Rosa, where precipitation records stretch back to 1902, rainfall has been recorded in about 80 of the past 120 years.

“It’s not completely rare to have rain like this in September,” Gass said.

Santa Rosa’s highest rainfall total for September was recorded in 1904, when 4.39 inches fell.

Last year, the city recorded a third of an inch of rain for the month. There was no measurable rainfall in September 2020; 0.12 inches for the month in 2019; 0.06 in 2018; and 0.52 in 2017.

You can reach Staff Writer Matt Pera at matthew.pera@pressdemocrat.com. On Twitter @Matt__Pera.