Last 2 weeks have been hottest recorded for this time of year in region, UCLA climatologist says

A second week of sweltering heat in Northern California brought record temperatures to Mendocino County but slightly lower highs in the North Bay as excessive heat warnings and advisories remain in effect.

In fact, according to a prominent California climatologist, the last two weeks have been the hottest recorded for this time of year.

Ukiah reached a high of 110 degrees Thursday, a tie with the previous record for that day set July 11, 1913, said Johnathan White, a meteorologist with the National Weather Service office in Eureka, which covers Mendocino, Del Norte, Humboldt, Trinity and Lake counties.

On Friday, highs in Santa Rosa are forecast to reach 96 degrees in Santa Rosa and 101 degrees in Windsor and Healdsburg. Temperatures will be slightly lower in Rohnert Park, at 92 degrees, and Petaluma, at 94 degrees. Temperatures in Napa County will range from the low-90s in Napa to 104 degrees in St. Helena.

High daily temperatures with limited overnight cooling prompted an excessive heat warning for the North Bay’s interior mountains, including parts of Sonoma and Napa counties. That is set to expire at 8 p.m. Friday.

An excessive heat advisory remains in effect until 9 p.m. Saturday for southwest inland portions of Mendocino County. And advisories for Sonoma and Napa counties are set to expire at 8 p.m. Friday, according to the weather service.

Daniel Swain, a climate scientist with UCLA, was inundated by media requests Friday afternoon after he posted to X, formerly Twitter, that the last two weeks “are now warmest late June through early July period on record across most of California,” in addition to areas of Arizona, Nevada and Oregon.

“I really have no reason to cast doubt on that statement,” Howard Diamond, climate science program manager at the National Oceanic and Atmospheric Administration’s Air Resources Laboratory, told The Press Democrat on Friday.

Howard said such analysis would take him more time.

“At this point, all I can do is to also provide you an anomaly plot of just how much above normal those temperatures are versus the long-term average from 1991-2020,” he said.

Places along the California coast were as much as 12 degrees above normal, he indicated.

This year’s seasonal average temperatures are up to 20 degrees above normal, according to meteorologists.

Last week’s high temperatures were “an unprecedented heat streak,” said Alexis Clouser, a meteorologist with the National Weather Service’s office in Monterey. “Temperatures above that level (seasonal averages) for that long and that duration is fairly rare.”

Napa and Sonoma typically experience average temperatures at this time of year in the low- to mid-80s.

On July 2, at the onset of the heat wave, Santa Rosa set a high temperature record of 105 degrees for the day. The previous record high was 103 degrees July 2, 1970.

The extreme heat presents a major risk to anyone who lacks access to water or ways to cool down. Agencies have cautioned people to be on the lookout for symptoms of heat exhaustion or heat stroke.

Signs of heat exhaustion include dizziness, thirst, heavy sweating, nausea and weakness. If you experience these symptoms, act fast: move to a cooler area, loosen clothing, sip cool water and seek medical help if your symptoms don’t improve.

Confusion, dizziness or becoming unconscious are signs of heat stroke. If you observe someone with these symptoms, call 911 immediately. Move the person to a cooler area, loosen their clothing and cool them down with water or ice.

Coupled with low relative humidity and wind gusts up to 25 mph inland, the continued high heat means elevated risk for wildfire.

Next week, Sonoma and Napa can expect a little cool-down and temperatures will get a bit closer to normal for the season, according to the weather service. Highs in Napa and Sonoma counties are forecast to range from the mid- to low-80s, with warmer spots like Cloverdale, Healdsburg and St. Helena generally in the mid- to upper-80s.

Inland areas of Mendocino County will also experience a slight cooling next week more in line with seasonal averages of upper-80s to low-90s, except for Ukiah, which will remain closer to 100 degrees.

You can reach Breaking News Intern Amy Moore at 707-526-8545 or amy.moore@pressdemocrat.com.

You can reach Staff Writer Sara Edwards at 707-521-5487 or sara.edwards@pressdemocrat. com. On Twitter @sedwards380.