Air quality in San Francisco and the Bay Area is predicted to slide into potentially unhealthy territory by Sunday, as an area of high pressure puts an end to the nice marine breeze we've been having for a couple of days that's pushed wildfire smoke away to the north and east.
It's been a lovely Friday so far around the Bay, and looks to be a pleasant and cool night as well, but things begin to change on Saturday. And after an end to a historic 30-day Spare the Air streak earlier this week, Saturday has been declared another Spare the Air day, as NBC Bay Area reports.
That high-pressure system is expected to push air quality into "yellow" or "moderate" territory by late Saturday, and that's expected to last into Wednesday, with "orange" or "unhealthy for sensitive groups" ratings possible as well.
"While the last two days brought a much-needed respite from the poor air quality the Bay Area has endured for the past month, air quality is again expected to be unhealthy due to continued impacts from wildfires," says Jack Broadbent, an executive officer for the air quality district, in a statement today about the Spare the Air announcement. "Residents should stay vigilant, track air quality conditions in their communities and head indoors if air pollution reaches unhealthy levels to protect their health."
Northerly winds are expected to begin pushing more of the Mendocino and Butte County wildfire smoke down toward the Bay, and the area of high pressure will keep it from mixing out quickly, according to meteorologist Kari Hall.
"It doesn't look like they'll be strong winds," says National Weather Service forecaster Brayden Murdock, speaking to SFGate. "Not looking at anything to transport that smoke too quickly. Hopefully nothing like what we had before."
The National Weather Service Bay Area desk continues to post helpful GIF animations of smoke forecasts every day, and below was the latest from Thursday.
Latest Smoke Model indicates generally light concentrations of near surface smoke across the #BayArea and Central Coast through Friday, except in the vicinity of the #DolanFire in southwest #MontereyCounty. #CAwx #CAFires pic.twitter.com/kAfZxWZKN9— NWS Bay Area (@NWSBayArea) September 18, 2020