As heat wave eases, stagnant air mass could trap smoke

A day after record heat melted much of the Bay Area, the thermometer went down a bit and the wind was barely more than a ripple.

Now about the smoke. “As we have this high pressure over us, it’s going to do very little for our winds, both at the surface and above us,” National Weather Service meteorologist Roger Gass said Tuesday. “So we’re going to have a pretty stagnant air mass with smoke settling in.”

How quickly and severely remains to be seen, forecasters said.

A Spare the Air alert remained in effect through Friday — the total for the year is a record 37 — and the air quality readings from the Bay Area Air Quality Management District were expected to get worse as Tuesday progressed.

At 11 a.m., Concord (74),

Livermore (72), Pleasanton (64) Napa (55) and San Jose (54) had official air- quality index readings between 51100, considered moderately unhealthy to breathe. The rest of the region, from Sebastopol in the North Bay to Gilroy in the South Bay to Oakland and Berkeley near the coast, the air was good.

Still, Gass and air quality forecasters said that the fine particulate matter probably would increase gradually, especially with smoke from fires starting to drift this way because of what small wind pattern there is.

Smoke from the Glass Fire burning in Napa County and the Zogg Fire in Shasta County continued to billow over the region as the fires roared out of control Tuesday. Areas in the North Bay were expected eventually to have unhealthy air later Tuesday, according to the district.

The hourly AQI readings did get as high 174 in Livermore on Monday night, a figure considered unhealthy for everyone.

Temperatures reversed course, going down dramatically along the coast after a marine layer settled in, Gass said. Temperatures were in the 50s and 60s throughout the region Tuesday morning, and by 2 p.m., they remained mild almost everywhere.

The region’s high spot was 95 degrees in Livermore, where it reached triple digits Monday, and Concord wasn’t far behind at 89 degrees. But in San Jose, the mercury read 83 a day after it hit a record 101. The temperature in Oakland at 2 p.m. was 83, and it was 68 in San Francisco.

Redwood City (98 degrees) and Oakland (96) also had record heat Monday, as did the San Francisco International Airport (96). All broke previous records high- temperature marks set in 2010.