The hottest temperature ever recorded in San Francisco is 106°F, set on September 1, 2017 at the downtown weather station. The hottest temperature recorded in the Bay Area is 116°F in Livermore, set on September 5 and 6, 2022. The 10-degree gap between those records shows how strongly the ocean protects the coast and how hot the inland valleys can get.
What Is the Hottest Temperature Ever Recorded in San Francisco?
San Francisco's hottest temperature on record is 106°F, recorded downtown on September 1, 2017, in records that begin in 1874. That broke the previous all-time high of 103°F, set on June 14, 2000, and the heat held into the next day, when downtown reached 102°F.
Both records came during heat domes, when strong high pressure crushed the marine layer and offshore winds replaced the usual cool ocean breeze. Without the sea breeze, San Francisco heats like any other city, and warm nights let each day start hotter than the last. The September 2020 and September 2022 heat waves pushed downtown to 100°F and 98°F, short of the record.
How Often Does San Francisco Hit 90 Degrees?
San Francisco hits 90°F or hotter on about 3 days a year downtown, based on 1991-2020 records. Most of those days come in September and October, when the marine layer weakens and offshore winds can reach the coast. The average high in September, the warmest month, is 70.2°F.
The rarity makes heat waves dangerous in San Francisco. Many homes have no air conditioning, so a 95°F day downtown can be harder on residents than a 105°F day inland. See Bay Area heat waves for how these events build.
What Is the Hottest Temperature Ever Recorded in the Bay Area?
The Bay Area's record is 116°F at Livermore, set on September 5 and again on September 6, 2022. That beat Livermore's previous record of 115°F from September 3, 1950. The same 2022 heat wave set an all-time record of 109°F in San Jose and pushed Concord to 112°F.
Inland records run far higher than coastal records because the marine layer's cooling fades with distance from the ocean and with every ridge in between. On September 6, 2022, downtown San Francisco reached 98°F while Livermore hit 116°F. On the worst days, valleys deep behind the hills get none of the ocean's protection, as our Livermore guide explains.
Are Bay Area Heat Records Getting More Common?
Bay Area heat records are being broken more often: Livermore and San Jose both set all-time highs in 2022, and San Francisco set its all-time high in 2017. A warmer background climate makes each heat dome hotter than the same pattern would have been decades ago. Individual records still need careful attribution, because each one depends on where the high pressure sets up and whether the sea breeze fails.
For heat safety, watch for heat advisories and extreme heat warnings, and check on neighbors without air conditioning. Remember too that the coast can heat up fast once the marine layer disappears. For how these events build, see Bay Area heat domes.
