Duration of Heat and Smoky Skies: An Overview – Update

Highs will range from the 70s at the beaches, 80s in San Francisco and Oakland, to 90s and lower 100s in Wine Country, the Tri-Valley and the Santa Clara Valley. Wildfire smoke is expected to impact air quality and visibility throughout the day, particularly in the northern and eastern portions of the Bay Area. Aside from the haze, cloud-free skies are forecast overnight for the supermoon.

Bay-wide heat

During the final days of August, it’s fitting that Wednesday’s heat has a taste of autumn to it. Winds down the Sacramento Valley will resemble an early autumn pattern, stomping out the marine fog deck for cloud-free skies all the way to the coast. A damaged marine layer will allow San Francisco and Oakland to warm up more than 10 degrees above normal.

Unlike last Wednesday, though, when San Francisco reached 85 degrees and Oakland hit 90, ocean temperatures are about 5 degrees cooler, which will keep some natural air conditioning intact. Haze from wildfire smoke could also knock a degree or two off what is expected on a clear day. High temperatures in downtown San Francisco are forecast to reach the lower 80s, with upper 80s in Oakland.

Widespread 90s are expected inland. Healdsburg, Fairfield, Vacaville and Concord could approach or surpass 100 degrees.

The heat isn’t expected to last long. Thursday’s Temperatures will be about 5 degrees cooler region-wide as onshore breezes and some fog return to the coast. Friday’s highs will drop 5 to 15 more degrees from Thursday, with partly cloudy skies across the Bay Area.

Hazy skies

Wildfire smoke from Northern California is expected to drift into the Bay Area on Wednesday, some of which is expected to reach the surface. Weather models predict locally higher smoke concentrations in the North Bay and East Bay. Ground-level ozone is expected to increase, prompting the Bay Area Air Quality Management District to issue a Spare the Air alert. Air quality is expected to be moderate to unhealthy for sensitive groups.

In addition to the incoming wildfire smoke, fire weather conditions are raised across Northern California due to low humidity and wind gusts up to 35 mph. A red flag warning is in effect for portions of the Sacramento Valley, North Coast and interior North Bay mountains until 8 p.m. Wednesday. Planned safety power shutoffs from Pacific Gas and Electric Co. are possible in places like Napa County, according to the company’s website.

Air quality is expected to gradually improve Thursday before completely clearing out Friday as a cold front sweeps through the area. Rain is also expected to fall on where the Happy Camp Complex fire is burning on Friday, accumulating around a tenth of an inch.

Wednesday breakdown

San Francisco: A cloud-free, yet hazy, morning is expected across the city. Temperatures will peak in the upper 70s in the Sunset and Richmond districts around 1 p.m. and lower 80s in downtown and South of Market around 2 p.m. Noe Valley, Glen Park, the Mission District and the Dogpatch could reach the mid-80s.

The air quality index is forecast to be moderate, but light ocean breezes in the afternoon should reel in some fresh air. Cloud-free skies are expected to persist into the evening. The supermoon should be visible over the Oakland Hills when it rises at 7:57 p.m. Overnight lows are expected to be near 60 degrees.

East Bay: Hot temperatures and poor air quality is forecast across the East Bay on Wednesday. Highs will reach the mid- to upper 90s for Walnut Creek, Dublin and Livermore. Haze and smog is expected to be exceptionally thick along the I-680 corridor. Air quality is expected to be unhealthy for sensitive groups across the East Bay.

Richmond, Alameda, Berkeley and Oakland will also experience their hottest day of the week, with highs in the lower 80s along the bay to upper 80s closer to the hills. Overnight lows will stay elevated in the lower 60s, with gradual air quality improvement into Thursday morning.