Cool air will prevail for most of this week, as the marine layer off the San Francisco coast gathers some strength after remaining pretty weak for two days.
Saturday and Sunday saw some declining air quality thanks to wildfire smoke blowing down from the north and settling closer to ground level. But that is changing by Monday afternoon, as the National Weather Service forecasts, with the marine breeze set to push the current smoke back further inland. By late afternoon, most of the North Bay and East Bay should see the haze clear out as well as the smoke gets "advected," as the meteorologists say.
(And, P.S., this is the 21st day in September, made holy by the Earth, Wind & Fire song "September.")
Did you remember to look at our smoke forecast for the 21st of September? 🎶— NWS Bay Area (@NWSBayArea) September 21, 2020
Smoke from the August Complex that has recently settled across the Bay Area, especially in the North Bay, will get advected (transported out) throughout the day by onshore flow.#CaWx #CaFire pic.twitter.com/72vspOmGFO
Later in the week, though, temperatures are going to start to go up again, with that typical-for-late-September pattern that often brings a heatwave to San Francisco the same weekend as Folsom Street Fair — which this is, but the fair is of course a virtual event this year.
A warming pattern looks to be beginning on Friday and Saturday, as Weather Underground tells us, with Sunday likely being the peak for high temperatures around the Bay Area.
The National Weather Service also forecasts a late-week heatwave, with temperatures potentially to hit 80-ish in San Francisco on Sunday, and 98 in places like Santa Rosa and Livermore.
Look into the future with me...🔮— NWS Bay Area (@NWSBayArea) September 20, 2020
Sunday 27 Sept 2020 High Temp Forecast
After cooling through the week, we may see the development of a late season heat event a week from now.
Keep the #sunscreen handy and watch the forecast closely.#cawx #caheat pic.twitter.com/AU3sx7UqWz
The warm temps are likely to stretch through Tuesday, September 29, which is potentially the day that San Francisco could restart indoor dining at limited capacity. But it looks like there will be nice nights for eating outdoors from about Friday through next Wednesday.