As the Bay Area’s first heat wave of 2025 began to crank up the thermometer on Thursday, the Bay Area Air District responded in a familiar way by issuing the season’s first Spare the Air alert.

The agency announced about 11:45 a.m. that the smog level for the region is expected to be unhealthy on Friday. The alert forbids people from burning wood and urges them to avoid driving to reduce the pollution.

The first extreme hot day of 2025 is expected to arrive Friday, according to the National Weather Service. Temperatures are expected to rise into the 100s in some spots of eastern Contra Costa County and into the high 90s in Livermore, Pleasanton, the Santa Clara Valley, Walnut Creek and Concord.

A bit of a preview came Thursday. Temperatures were expected to spike in the high 80s in the hottest areas — eastern Contra Costa County had a chance to hit 90 —  and by noon, temperatures throughout the region unofficially were running about 6-8 degrees warmer than at the same time Wednesday, according to the weather service.

In San Jose, the thermometer likely will reach 90 degrees; along the Peninsula, some spots may see the 80s; in Oakland and Richmond, it will reach the high 70s.

All of it is a byproduct of high pressure that will build throughout most of the state. Underlying conditions created by a lower-pressure trough in the upper part of the atmosphere near the Mexico-California border will keep that high pressure from developing a hard edge in the Bay Area; as a result, the heat wave is likely to be over come Saturday.

So, too is the air alert.

“We expect there to be cooler temperatures along with a sea breeze,” district spokesperson Juan Romero said. “So we don’t expect this will be for more than a day.”

By the middle of next week, temperatures in the hottest spots are expected to be back in the low to mid-70s, according to the weather service.

The air district issued 17 Spare the Air alerts a year ago.