A cool, breezy outlook brings the bonus of better air quality

If September was a weather rollercoaster, then last week was the peak rise of extremely hot temperatures, and today is the giant downfall.

Unusually cool temperatures are coming to North Bay and East Bay

The cooling trend kicks into high gear on Thursday as the sea breeze propels another round of 15-20 mph winds towards the SF peninsula. These winds will bleed quickly into SF Bay and travel to the delta where they disperse to towns like Walnut Creek, Fairfield and Livermore.

A few of these names should sound familiar given that they broke daytime high temperature records even as last week’s heat wave ended. Instead, those same towns can expect a cool, windy Thursday afternoon with temperatures hovering in the mid-70s.

Not only are these temperatures comfortable, but they are also about 5-10 degrees cooler than the average for this time of year in the East Bay. This means that these temperatures and winds are more like mid-spring than mid-September.

Air quality is also improving, after a week of smoke impacts. The Bay Air Quality Management District is forecasting low air quality index (AQI) readings for Thursday.

The smoke plume from the Mosquito Fire is expected to be carried away from central California by prevailing westerly winds on Thursday.

Gerry Diaz

The latest runs of the High Resolution Rapid Refreshment (HRRR) model clear smoke from the California coast as prevailing delta winds inject clean air from the Pacific into the East Bay and the rest of the Sacramento Valley. This breeze will help ease the hazy skies and make way for much more comfortable AQI levels on Thursday than seen in the previous days.

Enjoy the March, Bay Area weather!

Thursday Breakdown

• San Francisco: Another day with shallow fog on the west side followed by 15-20 mph gusts taking over most of the city by lunchtime. Look for highs in the mid upper 60s.

Another slight chance of drizzle is on the way in the morning for the Sunset and Richmond neighborhoods thanks to this cozy fog bank and then again in the evening.

• The Pacific coast: Patchy morning fog and a chance of drizzle are in store for residents along Highway 1 between Half Moon Bay and Pescadero on Thursday. Look for highs in the mid 60s and windy gusts of 15-20 mph before the fog returns tonight.

• North Bay: After days of dealing with a pesky haze, residents of Napa, Santa Rosa and Petaluma are in for a treat Thursday afternoon, with sunny skies, blustery gusts of 10 to 15 mph and 70s thanks to the breeze from San Pablo Bay.

The best part? Models are keeping the smoke out of the area this afternoon.

Similar conditions are forecast for residents south of Novato, with temperatures along the bay and the Sonoma coast approaching the low 70s this afternoon. Hold on to your hats as winds can blow up to 25 mph along the shore.

• East Bay: Low 70s, gusty bay winds and sunny afternoon skies all arrive in Oakland and all cities along the I-880 corridor Thursday afternoon.

Inland towns east of the I-680 corridor like Walnut Creek and Fairfield can expect similar temperatures. Look for daytime highs in the mid-70s and clear skies thanks to the cool, clean Pacific breeze entering the delta.

• South Bay and Santa Cruz: Whether you’re in the Santa Clara Valley or along Highway 17, a comfortable bay breeze will blow into every corner of the South Bay Pass and Santa Cruz Mountain this afternoon, keeping temperatures in the mid-1990s. 70.

Expect temperatures on the Santa Cruz coast to be closer to 70 degrees as patchy fog hangs over the coast in the morning. Otherwise, clear skies and occasional 10-20 mph gusts will be the main drivers of the weather from Capitola to Bonny Doon.

gerry Díaz (he/they) is an editorial meteorologist for the San Francisco Chronicle. Email: [email protected] Twitter @geravitywave

Dale D. Schrum