For Bay Area, haze expected for at least the next few days

A gray cloud cover mixed with a brownish hue of haze coated the Bay Area horizon Friday and was expected to do so through at least part of the weekend, according to the National Weather Service.

By Friday afternoon, air quality had sunk to “moderate” levels in parts of the Bay Area, with other areas showing readings that indicated the air was unhealthful for sensitive groups.

The phenomenon was being created by smoke from the Dixie fire in Butte and Plumas counties, as well as wildfires burning in Shasta and Siskiyou counties, mixing with a marine layer that often covers the Bay Area.

“The marine layer came in with the usual low clouds,” NWS meteorologist Drew Peterson said. “And then the smoke from the fires moved to the south, but they stayed above the marine layer.”

The result, Peterson said, is that the smoke was hanging low enough in the atmosphere to block out blue sky but not so low as to create unhealthful air conditions for most people.

Air readings by the Bay Area Air Management District for the Bay Area were mostly in the “healthy” tier Friday morning, but many locations in the East and South Bays were showing worse readings by the afternoon. Residents were advised to close windows and doors if they smelled smoke.

There was no such luck in other areas such as Lake Tahoe, where the air quality index measured by IQAir was as high as 220 on Friday afternoon.

IQAir is an air quality company that monitors particulate matter throughout the world, and any reading above 200 is very unhealthful.

The air quality also was bad in Sacramento, where the air quality index as measured by Sacramento Metropolitan Air Quality District hovered between 150 and 160 Friday afternoon, a reading that is unhealthful.

That area is being hit harder by smoky air than the Bay Area because onshore flow is influencing the smoke, as it is expected to do into today and perhaps longer, according to forecasters.

“An increase in the onshore flow on Saturday will push a lot of that smoke to the east into the Central Valley,” Peterson said. “That said, some of that smoke will linger, and more may come.”

Forecasters expect cooler weather today after a spike in the temperatures Friday.

The smoke itself was creating some condensation that could occasionally result in tiny amounts of measurable rain, forecasters said.

San Francisco received .05 of an inch overnight Wednesday into Thursday.

Mostly, the pattern simply created an odd-looking sky that at times appeared to shift color depending upon where you looked.

“Until we see a significant shift in the pattern, we’re going to continue to see this,” Peterson said. “And there’s just too much going on to see a clear longterm outlook.”