Skip to content

California heat wave: When will it end?

The worst of California’s heat wave has arrived for the final day of Labor Day weekend celebrations, with temperatures expected to rise as high as 110 degrees in St. Helena and Healdsburg. The intense heat has prompted warnings about possible rolling blackouts Monday on California electric grid.

What’s behind the sizzling temperatures? It’s called a heat dome: an atmospheric lid is trapping hot air over the Western US, triggering intense heat. You can read more here about the science of California’s worsening heat waves, as explained by the Chronicle weather science team.

Our reporters are fanning out today to bring you the latest news from around the Bay Area, and our meteorologist is on hand to talk through what he’s seeing ahead.

Latest updates:

Don’t go to Stinson Beach, Marin officials warn

“If you are not already at Stinson Beach. … we’d suggest not going,” the Marin County Sheriff tweeted Sunday. There are “hours-long delays getting into the area, and the parking lots and street side parking is all full.” On Sunday, the sheriff’s office said it had issued more than 145 citations in Stinson Beach. Visitors are requested not to block driveways or park in yards, and to be respectful of residents.

California lawmakers want to rank heat waves

On the desk of Gov. Gavin Newsom is AB2238, a bill that would direct the state’s Environmental Protection Agency to create a ranking system for heat waves by 2025. Hurricanes, earthquakes and even atmospheric rivers get ranked by their severity — so why not heat waves? It’s unclear how the current heat wave would rank, but officials say its extreme temperatures and long duration make it particularly dangerous. Read more here about the heat wave ranking bill, which was passed unanimously with bipartisan support.

Parking lots at Marin Beaches and near Golden Gate Bridge area are full

The Golden Gate National Recreation Area tweeted that parking lots in Stinson Beach, Muir Beach and Rodeo Beach in Marin County are full, as are most of its lots in San Francisco. “We welcome our visitors escaping the heat, and remind them to be patient, get shade, and don’t take chances with cold ocean currents or coastal bluffs,” the park service tweeted.

Dozens of beach-goers swarmed the Bay Area coast Saturday afternoon as temperatures started heating up ahead of an anticipated heat wave that has state officials concerned about heat-related illnesses and potential wildfires.

Dozens of beach-goers swarmed the Bay Area coast Saturday afternoon as temperatures started heating up ahead of an anticipated heat wave that has state officials concerned about heat-related illnesses and potential wildfires.

Greg Griffin/The Chronicle

Even San Francisco is already experiencing ‘extreme’ heat

Heat in San Francisco is considered extreme when it surpasses 85 degrees – and shortly before noon, the downtown reading was already at 89 degrees. The city will remain cooler than most parts of the sweltering region and state, however.

California grid boss says Tuesday demand expected to be highest ever

Amid scorching temperatures across California, the state’s electrical grid operator is forecasting the highest-ever demand for power in state history. Californians burned through 50,270 megawatts of power on July 24, 2006, but California Independent System Operator President and CEO Elliot Mainzer said Monday at a news conference that the expected demand has surpassed that historic high for Tuesday. He called on Californians to conserve their power during the key hours of 4 pm to 10 pm this week and hoped that those reductions and importing power from other states could get the state through Monday and Tuesday without rolling blackouts.

California grid issues emergency stage 1 notice

In a sign of the intense stress on power supplies caused by the heat wave, the California grid operator has issued an Energy Emergency Alert 1 notice for Monday, effective from 5 pm through 9 pm This is the first level-1 emergency alert for the grid so far this heatwave, and it is designed to lower power demand from large customers and create more supply. If the grid passes through emergency stages 2 and 3 — something grid officials think could happen Monday — then it is time for rolling blackouts because demand, sent sky-high by air conditioning use, is exceeding supply. Read more here about the nearly unprecedented strain on California’s power grid.

Fire danger is high across California

Officials are warning against any activity that could start a fire, as the extreme temperatures have further dried out vegetation and made it highly vulnerable to a spark. Fire danger is rated high through Friday in most of California.

How long will the heat wave last?

What feels like an endless heatwave is peaking on this Labor Day, with widespread 105-110° F temperatures coating the North Bay, East Bay and Sacramento Valley. Even San Francisco is getting in on some of the heat wave as parts of the city climb to the 80s today. This historic heat wave isn’t done with California yet. With the heat wave expected to drag out, all excessive heat warnings and advisories for the Bay Area and the Sacramento Valley have been extended through 8 pm. Thursday.

Fans take advantage of the shade while watching San Francisco Giants play the Philadelphia Phillies at Oracle Park in San Francisco on Sunday.

Fans take advantage of the shade while watching San Francisco Giants play the Philadelphia Phillies at Oracle Park in San Francisco on Sunday.

Scott Strazzante/The Chronicle

Hiker suffering from heat exhaustion rescued from Montara Mountain

Officials rescued a hiker who had experienced heat exhaustion at Montara Mountain in San Mateo County on Sunday, according to a tweet from Cal Fire’s CZU branch. Read here about officials’ warnings about outdoor exertion this weekend, following a string of high-profile heat-related deaths over the past year.

Flex alert in effect Monday from 4 pm to 10 pm

During that time, electric grid officials are asking Californians to refrain from using energy-intensive appliances such as dryers or dishwashers and turn off unnecessary lights. They also ask people to keep their air conditioning at 78 degrees or higher during that time (pre-cooling your home before 4 pm is a good idea). This is the latest in a string of Flex Alerts during the heat wave.

A biker rides by Lake Merritt during the heat wave on Labor Day weekend in Oakland.

A biker rides by Lake Merritt during the heat wave on Labor Day weekend in Oakland.

Michaela Vatcheva/Special to The Chronicle

Rolling blackouts a possibility on Monday

Power grid conditions are expected to deteriorate late Monday afternoon as air conditioners work overtime and electricity demand soars. Grid officials anticipate emergency conditions and will ask consumers and businesses to save power from 4 to 10 pm in a bid to avert rolling blackouts. Read more here about why grid officials are so worried.

What is a heat wave?

Heat waves are typically defined as unusually hot weather lasting more than two days. But what’s considered unusual can vary across California’s distinct geographical regions. For example, a high of 95 degrees Fahrenheit may describe a normal summer day in the Central Valley. But these temperatures could be unbearable in San Francisco, where residents typically don’t have air conditioning. Weather experts consider these differences when providing warnings about extreme heat. Go here to read more about the science of heat waves.

Leave a Reply

Your email address will not be published.