Amid a sea of purple and red dots last week, the air quality index readings on the coast stood out, showing yellow and green numbers in the 50s and below. That’s because coastal conditions often counter the worst of drifting smoke, local weather forecaster Jan Null said.
By the weekend, the whole Bay Area was showing moderate smoke levels on the AirNow Fire and Smoke Map, which are considered unhealthy only for people who are sensitive to smoke. The map, built by the U.S. Environmental Protection Agency, the National Weather Service, and other federal and local partners, shows a live view of air quality readings across North America.
Null, who founded Golden Gate Weather Services and lives on the Coastside, said most of the smoke from nearby fires that have recently exploded out of control has stayed above 5,000 feet. That’s why the sunsets last week glowed orange, even as on-the-ground air quality remained tolerable. And even as the Caldor Fire grew on Tuesday morning, the air conditions didn’t change much on the coast.
The Coastside advantage, Null said, is its position adjacent to the ocean. Offshore breezes, which are more prevalent during the summer and fall, push clean air from the ocean inland. Most of the time, that air is free of pollutants like smoke or industrial smog.
“It just never gets to us,” Null said.
But sometimes, winds come from the other direction, blowing south from Northern California, where the historic Dixie Fire is still raging, and toward the Bay Area. Air quality conditions on the ground can simply be a matter of which wind prevails.
Last week’s PG&E shut-offs, affecting 13 California counties and 50,000 customers outside of San Mateo County, were a result of dry offshore winds, which greatly increase the risk that a spark could ignite an uncontrollable blaze.
Although smoke hasn’t been a hazard so far locally, the coast is far from out of the woods this fire season. The Dixie Fire is just 35 percent contained after burning more than 700,000 acres over the past month. And closer to home, the Caldor Fire remains entirely uncontained, having grown to more than 80,000 acres. As fall approaches, high winds that have the potential to spark new fires will only become a greater concern.
“The Wine Country fires last year happened in October, and the Camp Fire in Paradise was in early November,” Null said. “That’s typically when we see those bigger fires.”