Without any wind, firefighters can tame some of the fires burning up and down the West Coast. But without wind, the smoke from those fires just sits over entire regions making the outdoors dangerous, and the built-up smoke blocking the sun's warmth is itself perpetuating the cycle by keeping breezes low.
"We’re talking five days of deteriorating air quality, lower than normal temperatures because of smoke cover, no sunlight, no appreciable winds trying to mix things out," says National Weather Service forecaster Brian Garcia, speaking to SFGate on Friday. "For it to linger around like this for five days in coastal California, I’ve never seen it before."
As we noted this morning, little motion in the current smoke mass is expected through today, and Garcia seems to suggest that nothing much will change until Sunday or Monday. The tweet below from the weather service's Portland bureau was a bit more optimistic, showing some dispersal of the smoke beginning today and suggesting that a "modest westerly breeze" would be moving in (at least over Oregon) in the "next couple of days."
Marine air begins to work inland over the next couple of days with a modest westerly breeze. This will allow air quality and visibilities to begin to improve over northwest OR and southwest WA, as seen in this computer model for today (Fri). Purples depict the densest smoke. pic.twitter.com/U7ADxX4smw— NWS Portland (@NWSPortland) September 11, 2020
And this tweet from another meteorologist also shows signs of hope over the Pacific.
Winds of change? Could see more wind toward the end of the weekend / early next week which would provide better mixing of the atmosphere / air quality as a storm system approaches the Pac NW. stay tuned. #CAwx #FireWx🤞🏻🙏 pic.twitter.com/xF7kXwleBY— Rob Mayeda (@RobMayeda) September 11, 2020
As SFist has explained to newcomers many times, the typical summer pattern in San Francisco is created by the collision of the ocean to our west, and the hot valleys to our east, just over the East Bay hills. When hot air gets hotter in the Central Valley in the summer, it rises and causes cool ocean air to be pulled inland in a steady westerly breeze. Usually that is accompanied by the marine layer that, in July and August especially, keeps San Francisco shrouded in cool gray fog well into the afternoon on many days, until it burns off. (Down on the Peninsula where the land mass is wider and there are more hills near the coast, that marine layer burns off long before reaching the Bay, leaving places like Palo Alto pretty toasty when SF is freezing.)
San Francisco gets heatwaves like the one we had last week when high pressure systems show up on the coast and temperatures suddenly even out, sometimes pulling air the opposite direction from east to west.
But now, we're stuck. The inland air is similar in temperature to the coast because the sun is being blocked out everywhere by ash and smoke, and thus it's at a standstill.
"Light overnight winds allowed smoke to seep down from above the shallow marine layer, resulting in widespread Unhealthy & Very Unhealthy conditions," explains the Bay Area Air Quality District on Twitter.
As Garcia tells SFGate, "I’ve worked in California for almost 11 years and it’s not about how bad [the air quality] is. It’s about the duration of this. If you remember 2018, we had smoke from the Camp Fire. That air quality was horrible... But that lasted only a day or two. Then we had wind come in from the east and blow it out. We have no wind right now."
Sorry, everyone! The weekend may be somewhat ruined but at least most of the Bay Area isn't on fire anymore!
The SCU Lightning Complex reached 98-percent containment as of Friday morning. The LNU Complex is at 95-percent containment; and the CZU Complex is at 85 percent. The biggest fires are now in Mendocino County — where two huge fires just merged making the August Complex the largest in state history — Butte County, and up in Oregon south of Portland.