San Francisco's July fog keeps the city cool while heat waves scorch the rest of the country, but neighborhoods like the Mission run up to 15°F hotter than the Sunset due to geography and urban heat island effects.

On the 2400 block of Mission Street, the afternoon sun hits hard. Down the coast in the Outer Sunset, the same July afternoon means jackets and Karl the Fog rolling through the Golden Gate.

The split isn't just atmospheric—it's measurable. While a massive heat dome baked over 200 million people across the central and eastern United States in late June and early July 2026, with cities from Philadelphia to Chicago hitting 90°F to 100°F, San Francisco International Airport averaged 66.9°F for the full month of July. That's barely a degree warmer than the historical average, according to WeatherSpark data.

But the city isn't one climate zone. The Mission District runs 8 to 15°F warmer than the Outer Sunset on summer afternoons, thanks to geography and urban heat island effects. The Twin Peaks ridge rises to 922 feet and functions as a geographic barrier that blocks marine air flowing from the Pacific, while the Mission sits in the fog shadow. The neighborhood logged 2,317 311 requests in the last week—many likely related to heat conditions—while the fog belt stayed comfortably cool, according to DataSF's Neighborhood Pulse.

The contrast shows up in the city's planning documents, too. San Francisco has the lowest air conditioning rate in the U.S., yet extreme heat days (over 85°F) are projected to rise from an average of 3 per year to 15 by century's end. The city's Heat and Air Quality Resilience Plan outlines over 30 strategies, though funding for the Environment Department dropped from nearly $3 million in 2022-2023 to about $600,000 for FY 2026-2027, according to reporting by Audrey Mei Yi Brown in the San Francisco Public Press. Mayor Daniel Lurie's recommended budget would eliminate general fund dollars for the Climate Equity Hub, a program that helps low-income households with energy efficiency retrofits.

The fog that some complain about is actually climate moderation in action. Long-term trends show it's declining by 33% between 1950 and 2010, based on airport weather records compiled by the Public Policy Institute of California. That shift means fewer of those cool summer afternoons and more days when the Mission's heat spreads citywide.