Summer presented itself on the first day of the season with a furnace blast felt around the Bay Area on Tuesday as residents adapted to the scorching temperatures as best they could.
Still, forecasters already were watching the developing conditions that could, within days, bring the danger of dry lightning — storms that could carry little rain but plenty of fire danger for the drought-parched region.
The high pressure had an obvious effect Tuesday as the mass of hot air sent temperatures soaring toward triple digits in the far East Bay interior, the Santa Clara Valley and the North Bay. The National Weather Service issued a heat advisory Tuesday that was in effect through the evening for the East Bay coastline, the Santa Clara Valley, the Santa Cruz Mountains and the inland areas of Contra Costa, Napa and Sonoma counties.
New daily heat records were set at the San Jose and San Francisco international airports, according to the National Weather Service. The former saw a high of 102 degrees, edging out the previous record of 101, and the latter saw a high of 98 degrees, shattering the previous record of 94. Both previous records were set in 1973.
The Oakland Museum of California tied its previous record of 98 degrees set in 1981.
Elsewhere, the mercury topped 104 degrees in downtown Santa Rosa, 100 degrees in Kentfield, 95 degrees at the Salinas Airport and 92 degrees in downtown San Francisco.
“(The heat) doesn’t really bother me,” said Manuel Santillan, who was shopping at a San Jose grocery market Tuesday. After living in Palm Springs, he said, he moved back to San Jose about a year and a half ago.
“It was a lot cooler (inside the market) than it was inside (my home),” he said. “That’s what drove me to come out here, because it was so warm inside my apartment. If you don’t have AC, it’s a lot nicer outside.”
The high-pressure air mass causing the heat also contributed to a Spare the Air Alert issued by the Bay Area Air Quality Management District on Tuesday. Residents were advised to avoid traveling by car to minimize additional pollution.
Those temperatures all are expected to go down by an average of 7-12 degrees Wednesday — the Bay Area’s high spots are expected to reach the mid- to high 90s — in part because of declining air pressure.
A “very weak area of low pressure” off the central California coast was pulling in moisture from a system in the southern desert, weather service meteorologist Roger Gass said Tuesday. That moisture is likely to create thunderstorm conditions in the atmosphere above 15,000 feet, he added.
“As it does, a lot of rainfall that (the system) could create will go away before it hits the ground,” he said. “That could create lightning with no rainfall associated with it. I wouldn’t call it an electrical storm, but I would call it a possibility of isolated strikes. We are watching it.”
Dry lightning caused a series of fires that grew into a major Bay Area wildfire complex in 2020 and sparked red-flag fire warnings again in 2021.
“It’s a very difficult thing to forecast where and when that might be,” Gass said. Even if the rainfall hits the surface, it’s usually disconnected to where the lightning actually strikes.”
The better news for the Bay Area region is that it remains uncertain whether any dry lightning will make it this far north. Gass said dry lightning was most likely in the southern Sierra Nevada. Climate expert Daniel Swain via social media said the system is expected to cut a swath through Central California but that the potential for thunderstorms was decreasing.
“The chances of them developing at this point are probably only about 10-15 percent,” Gass said. “But obviously, we’re watching it closely, because those thunderstorms and lightning without rain can have a high impact.”
Dry lightning caused approximately 650 wildfires that burned at least 1.5 million acres across Northern California in August 2020.
The high temperatures are expected to linger for a few days, dipping by the end of the week. San Jose and inland parts of the East Bay could see temperatures in the 90s through Friday. By next Tuesday, areas such as Concord, Livermore and the Santa Clara Valley may be back into the 80s.
Cooling centers were open for those seeking reprieve from the heat in Santa Clara and Contra Costa counties.
The U.S. Drought Monitor report, issued Thursday, showed that 97% of California and the entire Bay Area is in a state of severe drought or worse. Sixty percent of the state is mired in extreme drought, and 12% was in exceptional drought.
Tuesday’s weather did not bring a critical fire threat because winds were not particularly strong, Gass said. The fire concern was the greatest across the North Bay hills, where the winds were the breeziest. As of 1 p.m. Tuesday, there had not been any major wildfires reported in the North Bay.
“It’s very dry out there,” Gass said. “You can see all the vegetation has dried up as it usually does this time of year. This air mass is very dry as well. We’re not expecting significant fire threat across the Bay Area, but you don’t want a spark to start a fire. People need to be mindful of any outdoor activities — it doesn’t take much for a fire to start in these kind of conditions.”
Staff writer Jason Green contributed to this report.
