A HEAT WAVE that blanketed Northern California over Labor Day weekend and into this week sent temperatures soaring along with the tempers of Bay Area residents forced to cope with the threat of rolling blackouts and calls to conserve electricity.

Late Wednesday, more than 525,000 PG&E customers across the region waited anxiously to find out if they would have their power interrupted as the utility worked to keep up with soaring demand.

In the Bay Area, heat-related issues with equipment had already downed electricity to about 20,300 PG&E customers in the South Bay, and another 5,100 around the region as of 5 p.m., according to PG&E.

The California Independent System Operator directed the state’s utilities to prepare for rotating power outages, PG&E spokesperson Deanna Contreras said late Wednesday afternoon.

As of 5:15 p.m., the ISO website showed capacity at 56,737 megawatts and demand at 49,585 megawatts. The grid operator hadn’t asked PG&E to implement outages as of that time.

Tips for how to save energy during a Flex Alert. (Image courtesy of California Independent System Operator/Twitter)

However, “out of an abundance of caution” PG&E gave advanced notification to approximately 525,277 customers to prepare for potential rotating outages, according to a news release.

Energy providers this week have been pleading with customers to conserve power, even as some cities have seen their all-time record high temperatures eclipsed, resulting in more people cranking up fans and air conditioners.

Cal ISO has issued a series of Flex Alerts that urge customers to conserve power from 4 to 9 p.m. During the alert period, people are asked to set their thermostat to 78 degrees or higher, avoid using of major appliances and turn off unneeded lights.

Customers can visit PG&E’s website to check to see if they might be affected by rolling outages.

It appears that the public has answered the energy-saving call — at least for now. Cal ISO said it was able to avoid rolling blackouts in the Bay Area on Tuesday evening thanks to customers voluntarily reducing their impact on grids.

“Thank you, California!” the state’s power grid operator wrote on Twitter late Tuesday after flirting with its highest-ever peak power demand. “Consumer conservation played a big part in protecting electric grid reliability,” Cal ISO wrote on Twitter.

Power grid peak demand hit 52,061 megawatts Tuesday, a new all-time record for the state, according to Cal ISO. However, a possible need for a “load-shed” of strain on the grid was still not necessary and outages were avoided.

The Governor’s Office of Emergency Services credits a cellphone alert that went out to targeted counties on Tuesday at 5:45 p.m. Reminding people conserve energy.

“Conserve energy now to protect public health and safety,” the text reads. “Extreme heat is straining the state energy grid. Power interruptions may occur unless you take action. Turn off or reduce nonessential power if health allows, now until 9 p.m.”

As a result, the state’s energy grid reflected a “significant drop in energy use,” according to the Governor’s Office of Emergency Services.

Setting records

Meanwhile, six cities in the greater Bay Area on Tuesday saw their highest temperatures ever recorded, according to the National Weather Service.

The same cities were among seven that had record highs for September and among eight that set records for Sept. 6. In all, 21 record temperatures were set or tied Tuesday.

Livermore’s high of 116 degrees tied the all-time record high set only Monday, surpassing the previous mark of 115 set in 1950. King City’s high was also 116 Tuesday and broke by one degree the record set in 2017.

Other all-time highs were recorded in Santa Rosa (115, previous 113 in 1913), Napa (114, previous 113 in 1961), Redwood City (110, tied with 110 in 1972), and San Jose (109, previous 108 in 2017.)

This same six cities set records for the month and date.

In addition, Gilroy’s high of 113 surpassed the previous record high in September of 112 set Monday, as well as setting a new mark for Sept. 6 surpassing the mark of 112 set in 2020.

Tuesday’s high of 81 in Half Moon Bay surpassed the record high for Sept. 6 of 80 set in 2004.

Cooling centers extend hours

Officials in several communities announced they were keeping cooling centers open as the current heat wave continues.

Calistoga, San Leandro, Santa Rosa and Stockton officials — along with Sonoma County — announced that their centers will remain open until at least Thursday.

The Calistoga Community Center, at 1307 Washington St., will be open Thursday from 2-8 p.m.

San Leandro’s air-conditioned main library, at 300 Estudillo Ave., will be open Thursday from 8 a.m.-10 p.m., with free Wi-Fi, water and ice and resource kits.

In Santa Rosa, the Finley Community Center, at 2060 W. College Ave., will be open Thursday from 11 a.m.-7 p.m.

In Stockton, these centers will be open from 8-5 p.m. through Friday:

• Boggs Tract Community Center, 533 S Los Angeles St.;

• Garden Acres Community Center, 607 Bird Ave.;

• Kennedy Community Center 2800 S. D St.;

• Northeast Community Center, 2855 E. Harding Way;

• Taft Community Center, 389 W. Downing Ave.;

The hours are different for these Stockton centers that will be open from 9 a.m.-8 p.m. Thursday, and from 9 a.m.-7 p.m. Friday:

• Arnold Rue Community Center, 5758 Lorraine Ave. (hours not provided);

• Stribley Community Center, 1760 E. Sonora St. (hours not provided); and

• Van Buskirk Community Center, 734 Houston Ave.

The Seifert Community Center, at 128 W. Benjamin Holt Drive, will be open from 2-8 p.m. Thursday, and from 2-7 p.m. Friday.

In Sonoma County, officials listed more than a dozen sites where residents can escape the heat, in addition to county library branches that are open from 10 a.m.-6 p.m. every day but Sunday:

• Coddingtown Mall (10 a.m.-8 p.m. Thursday through Saturday and 11 a.m.-6 p.m. on Sunday);

• Santa Rosa Plaza (10 a.m.-8 p.m. Thursday through Saturday and 11 a.m.-6 p.m. on Sunday);

• Cloverdale Senior Multi-Purpose Center, 311 N. Main St. Cloverdale (1-4 p.m. Thursday);

• Cloverdale Library, 401 N. Cloverdale Blvd. Cloverdale (11 a.m.-6 p.m. Thursday through Saturday);

• Healdsburg Senior Center, 133 Matheson St. (9 a.m.-7 p.m. Thursday, 9 a.m.-5 p.m. Friday);

• Petaluma Community Center, 320 N. McDowell Blvd. (11 a.m.-7 p.m. Thursday);

• Rohnert Park Senior Center, 6800 Hunter Drive (9 a.m.-4 p.m. Thursday);

• Rohnert Park Community Center, 5401 Snyder Lane (8 a.m.-7 p.m. Thursday);

• West County Community Services, Russian River Senior Center, 15010 Armstrong Woods Road, Guerneville (9 a.m.-3 p.m. Thursday and Friday);

• Finley Community Center, 2060 W. College Ave., Santa Rosa (11 a.m.-7 p.m. Thursday);

• Sebastopol Community Cultural Center, 390 Morris St. (10 a.m.-4 p.m. Thursday and Friday);

• Cooling Center at the Grange Hall in The Springs hosted by SOS, 18627 Highway 12, Sonoma (9 a.m.-3 p.m. Thursday and Friday); and

• Windsor Senior Recreation Center, 9231 Foxwood Drive, Windsor (9 a.m.-6p.m. Thursday and Friday).

Bay City News staff writers Katy St. Clair, Kathleen Kirkwood and Jeff Ballinger contributed to this story.