17-07-2025
- Climate
- San Francisco Chronicle
Maps show how the Bay Area has been unusually cold this summer
Summer in the Bay Area hasn't been this mild in decades.
As heat waves roast much of the West, the Bay Area has been spared from extreme temperatures over the course of the last two months.
San Francisco International Airport has measured its coldest first half of summer since 1965. The average maximum temperature at the airport was just 67.6 degrees from June 1 through July 15.
Summer is also off to a cooler-than-normal start in Oakland, Santa Rosa and San Jose. These cities are trending slightly warmer than 2023, which began extraordinarily chilly throughout California before a hot finish.
This summer has been a stark contrast from 2024, which shattered temperature records across the state. July was historically hot in the Bay Area. Alameda, Contra Costa, Napa, Santa Clara, Solano and Sonoma counties had their hottest month on record.
Thirty-eight of the first 45 days this summer in San Jose have been cooler compared to the same time period in 2024. That includes Independence Day, which was 93 degrees last year but just 76 degrees this year.
The big difference this summer is the lack of a persistent high-pressure system over the West, a feature generally associated with hot, dry weather. Last year, the area of high pressure was anomalously strong over Northern California, yielding many 100-degree days in the valleys. Subtle dips in the upper atmosphere this year have kept chilly ocean breezes continuously blowing into the Bay Area.
So far this summer, NorCal has been in a sort of "goldilocks zone" for synoptic (large-scale) weather patterns.
Our two sources of big summer heat, the Four Corners high and the offshore high, have stayed in their places allowing onshore winds to dominate.
— Heather Waldman (@KCRAHeather) July 15, 2025
Unlike 2023 — when the first half of summer was cool across almost all of California — the chilly conditions have been confined to the Bay Area in 2025. The upper atmospheric pattern in 2023 chipped away at the Four Corners high-pressure system and prevented heat waves from building across the Southwest.
With mid-range forecasts favoring cooler-than-normal weather through late July, it would likely require a scorching hot August for the Bay Area to catch up to average summer temperatures.
This year is an anomaly amid an era of rapid warming. Bay Area temperatures warmed by an average of 1.7 degrees from 1950 to 2005 and are predicted to increase by several more degrees by the end of the century as human-caused climate change continues.
