The latest heatwave headed our way is coming with an "excessive heat warning" covering much of the Bay Area that begins on Saturday morning. And while smoke in the air seems to be clearing around most of the region on Thursday, a high pressure system combined with fires that aren't fully extinguished means we could have more hazy, choky days to come.
The National Weather Service upgraded its "excessive heat advisory" to an "excessive heat warning" for just about every Bay Area county besides San Francisco starting at 11 a.m. on Saturday. The immediate coast may see highs of 85 degrees this weekend, but just inland those temperatures are expected to rise higher — with possible max inland temps hitting a desert-like 115 degrees.
UPGRADE: the Heat Watch has been upgraded to an Excessive Heat Warning: w/ adding the N. Salinas Valley. Little heat relief will be near the coast. A Heat Advisory has been issued for coastal areas— NWS Bay Area (@NWSBayArea) September 3, 2020
Valid from Saturday at 11 AM to Monday at 9PM PDT#CAwx #LaborDayWeekend pic.twitter.com/BGhGbmIlX8
According to Weather Underground, SF is only going to see highs of 79 on Sunday and 81 on Monday, though that's not accounting for microclimates, etc.
Head to Napa, Sonoma, Contra Costa, or Alameda County, particularly over the hills and into inland valleys, and it is looking to be a real scorcher — made all the more unpleasant if our air quality goes back into unhealthy zones.
ABC 7 reports that a heat watch goes into effect Saturday morning and extends through Monday night, with the towns of Fairfield and Livermore likeliest to see highs over 100 degrees.
If you look back to Labor Day weekend 2017, a similar hot weekend was predicted with San Francisco exempted from the extremes of the heatwave. But in actuality, SF's highs set records that weekend due to unpredicted shifts in wind patterns, hitting 106 degrees downtown on September 1 — 20 degrees higher than was forecast. So, anything can happen!
The radar image below shows most of the smoke from the remaining fires in the region getting blown to the north and west of us today, with Sacramento seeing some of the worst of it. But as the National Weather Service notes, things may not look so great as we get into Friday and Saturday when those onshore breezes die down and/or become offshore breezes.
Updated Near Surface Smoke graphic shows modest improvement, but with fires still burning and high pressure building, expect it to linger. pic.twitter.com/76u22J4qmX— NWS Bay Area (@NWSBayArea) September 3, 2020
San Francisco's air quality is either "yellow" or moderately bad right now, or "orange" meaning "unhealthy for sensitive groups," depending on where you look.
Photo: Scott Goodwill