San Francisco is entering the three-week stretch that’s historically its warmest of the year, with average highs normally at or above 70.5 degrees. Instead, the city spent the weekend stuck in the upper 50s and low 60s under thick fog and drizzle. Sunday’s high of just 60 degrees tied for the coolest September day the city has seen since 2016.
What’s driving the chill
A slow-moving low-pressure system parked over Central California is the culprit. Because it’s cut off from the jet stream that normally steers weather systems through quickly, this one is taking its time crossing the state, keeping clouds thick enough that San Francisco’s usual fog isn’t burning off during the day the way it typically would. Onshore winds are also picking up through the afternoons and evenings, with gusts of 20 to 30 mph possible through gaps, passes and the northern Salinas Valley.
A small but real fire weather risk
The same system has pushed some convective activity toward the Central Coast, and forecasters are watching for isolated lightning early today, especially near the Santa Lucia Range. The National Weather Service has called the risk very small this time, but the setup is worth understanding regardless…