Bay Area Experiences Record-Breaking Cool Summer; Wildfire Risk Temporarily Reduced
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SAN FRANCISCO, CA – August 15, 2025 – The San Francisco Bay Area is experiencing an exceptionally cool summer, with numerous cities reporting their lowest maximum temperatures in recent history. This unprecedented chill,lasting throughout June and July,has significantly impacted regional weather patterns and temporarily lowered wildfire risks.
Record Low Temperatures Across the bay Area
A widespread cool spell has affected the entire Bay Area, with maximum temperatures failing to reach typical summer highs. The following cities have reported their lowest maximum temperatures stretching back to at least 1940:
- Concord
- Calistoga
- Santa Rosa
- Graton
- Kentfield
- San Jose
- Redwood City
- Fremont
- Hollister
- Napa
- Hayward
- Big Sur
- Oakland
- Monterey
Ancient Context: When Was It Last This Chilly?
The prolonged cool conditions haven’t been seen in decades. Petaluma Airport recorded its coldest June and July combined as record-keeping began in 1902. Oakland International Airport (OAK) experienced its 10th coldest first two months of summer on record, while San Jose International Airport (SJC) saw its 8th, and San Francisco International Airport (SFO) its 7th. The majority of Bay Area residents have not experienced such a sustained period of cool summer weather this century.
Specifically, 2025 marks SFO’s coldest summer as 1965, OAK’s sence 1975, and SJC’s coldest since 1999. Data from the National Weather Service indicates average temperatures in June were 8-12 degrees Fahrenheit below normal across much of the region.
The Cause: A Disrupted Jet Stream
Normally, high-pressure systems over the Four Corners region and the Pacific Ocean dominate Bay Area summers, deflecting the jet stream northward and ensuring warm, dry conditions. Though, this year, these high-pressure systems failed to develop as was to be expected.
The absence of these high-pressure zones allowed the jet stream to dip further south, bringing increased moisture and cooler temperatures to California. This southward shift resulted in persistent cloud cover and frequent marine layer intrusions, suppressing daytime heating. The jet stream’s position was influenced by a larger-scale atmospheric pattern known as the Pacific Decadal Oscillation (PDO), currently in a cool phase.
Meteorologists now report the Four Corners High is beginning to strengthen, signaling a return to more typical summer temperatures, though not expected to reach extreme levels.
Impact on Wildfire Season
The cooler, wetter conditions have provided a temporary reprieve from wildfire threats during California’s peak fire season.Increased fog and cloud cover have significantly boosted fuel moisture levels in vegetation.
Higher fuel moisture makes it more tough for fires to ignite and slows their spread.However,forecasters predict fuel moisture will decrease as the high-pressure system establishes itself,potentially increasing fire risk in the coming weeks. CAL FIRE spokesperson, Jonathan Cox, stated on August 14th that while the current conditions are favorable, vigilance remains crucial.
For Bay Area weather inquiries, contact CBS News Bay Area meteorologist Zoe Mintz at zoe.mintz@cbs.com.
