2017 is Santa Rosa’s hottest summer ever

In 115 summers, Santa Rosa has never had one like this before.

The summer of 2017 is now the hottest in Santa Rosa history, coming on the heels of the wettest winter in the city’s history.

The analysis, based on National Weather Service records that date back to 1902, does not even include the latest heat wave that blistered the region and made Sept. 1 the hottest day of the year with a high of 110 degrees.

Though summer does not end until Sept. 21, the weather service traditionally measures summer temperatures from June to August.

During that three-month period, downtown Santa Rosa had a daily average temperature of 69.3 degrees, beating a record 69 degrees set during the summer of 1981.

“It’s very significant,” said Steve Anderson, a forecaster with the weather service. “I mean, it’s never happened ever in the period of record.”

Ukiah, too, is having its hottest summer ever, with a daily average temperature of 75.3 degrees, according to the weather service.

The town’s previous hottest summer was in 2014, when the daily average was 74.6 degrees.

And, in fact, the entire state is having its hottest summer ever - for the second year in a row, according to statewide weather data obtained by Daniel Swain, a UCLA-based climate scientist who operates the blog Weather West. The daily average for the state? 73.6 degrees.

“This year once again puts an exclamation point on a sustained, long-term warming trend over the past century in California,” Swain wrote in a post published Saturday.

“Increasing frequency and intensity of extreme heat waves is one of the clearest hallmarks of our warming climate, and it’s likely that ‘extreme’ temperatures like those experienced this summer will become fairly routine in just a few decades.”

Santa Rosa’s summertime record, while legit, is officially unofficial, Anderson said, because downtown Santa Rosa lacked a government-sanctioned climate station from 2013 until this August, when one was placed in the backyard of a Santa Rosa family’s home.

During those summers, the records were officially kept by a 20-year-old station at the Charles M. Schulz-Sonoma County Airport because the weather service couldn’t find anyone in downtown Santa Rosa to take on the task.

According to the airport station, Santa Rosa’s daily average summertime temperature was 68.7 degrees, a record for that location as well - beating a 2006 daily average summertime temperature of 68.1 degrees.

During that three-year period, while the official temperature data came from the airport, Anderson kept a digital station at the McDonald Mansion, which provided unofficial daily temperature readouts for downtown Santa Rosa.

It’s thanks to those figures that Anderson is confident in the historical nature of this summer’s heat.

“A record is a record,” he said.

Much in the way that Santa Rosa’s history-making 60.39 inches of rain during the weather year ending later this month - the town got another 0.02 inches Thursday - set a record more for its constant, nagging presence than any Earth-shattering storms, so too has been the story of this season’s heat.

Until Sept. 1, which doesn’t count in this summertime assessment, Santa Rosa only had one day of record heat - June 18 - when the mercury climbed to 102 degrees.

It was just an overall very wet winter, followed immediately by an overall very warm summer.

“That’s typically what we would see with climate change,” Anderson said.

“The number of and more frequent extreme events. Flooding, rain, heat, hurricanes. All that kind of weather phenomena. We’ll just see more of those extreme weather events in the future.”

As for the week ahead, Santa Rosans can’t expect any record-breaking heat, but Sunday’s high should get up into the mid-90s, Anderson said, with a cooling trend bringing temperatures down to the mid-70s by week’s end.

You can reach Staff Writer Christi Warren at 707-521-5205 or christi.warren@pressdemocrat.com. On Twitter @SeaWarren.