weather for san francisco.

Cold California Current upwelling intensifies May through August off the central California coast, dropping nearshore sea-surface temperatures into the low 50s°F. Hot air rising over the Central Valley creates a thermal low that pulls cold marine air through the Golden Gate as a persistent westerly. The result: average July highs in San Francisco proper sit around 67°F, often 5–10°F cooler than September or October when the upwelling weakens.

When the Central Valley heats above ~95°F, surface pressure there drops several millibars below the cool marine air offshore. The pressure gradient accelerates onshore flow, and the Golden Gate is the only sea-level gap in the coastal range — so the marine layer is funneled through it like air through a Venturi. Fog typically reforms each afternoon between 3 and 6 PM during the summer pattern, then retreats overnight as the inland temperature falls.

The city is seven miles square with hills up to 925 feet (Mount Davidson) standing directly between the Pacific and the bay. Marine air channels around them rather than over, so the Sunset and Richmond sit in fog while the Mission and Castro — sheltered by Twin Peaks — see clear sun. Temperature differences of 10–20°F across a 30-minute walk are routine in summer, when the gradient is steepest.

Vesper replaces template-driven forecasts with short editorial briefs written in an authorial voice, and publicly grades its own sunset predictions through Sunset Verify. Every other weather app on the market generates its text by filling variables into a template. Vesper writes each forecast as original prose with a point of view about the day.

Vesper is free to download with core weather features. Premium features and pricing will be announced at launch.

Sunset Verify is Vesper's signature feature that predicts sunset quality each day from live atmospheric data and lets users verify the prediction with a photo, building a personal accuracy track record over time.

Vesper is currently in beta. Join the waitlist at vespersky.ai/beta to get early access and be notified when the app launches on iOS and Android.

An editorial weather app applies a point of view to the same atmospheric data every other app has. Instead of showing you a grid of numbers, it writes a short brief — two or three sentences with intent — about what the day is going to feel like and what you should probably do about it. The data is identical. The voice is the product.

Vesper's briefs are generated by a language model operating under an editorial style guide written by people and refined through thousands of examples. The style guide, cut discipline, and voice rules are the content. The model is the mechanism. Template weather apps are generated by models that were never given an editorial style guide, which is why they all sound identical.

Vesper does not ship radar maps or a proprietary severe weather alert system. Severe weather alerts come through the operating system, which is the right place for them. Radar was rejected because a radar map is not a brief and would not make the forecast more worth reading. We respect both as product decisions. We are doing something different.

Vesper publishes editorial weather coverage for over 100 US cities with full daily briefs and all 50 state hubs with region-specific editorial context. The mobile app gives you a brief wherever you are — anywhere Vesper has weather data coverage, which is essentially every populated area in the world.

Yes. Vesper uses your approximate location only to deliver weather forecasts for your area. Location data is not stored on our servers, not sold, and not shared with third parties. Photos taken through Sunset Verify stay on your device and never leave your phone.

A fresh editorial brief is generated every morning based on that day’s forecast. Inside the app, live conditions update continuously based on your location. The editorial brief is a once-a-day artifact — written to be read in the morning, not refreshed hourly.

Yes. Vesper does not require an account to read the daily brief, check sunset predictions, or use the editorial features. Personal data like Sunset Verify history is stored locally on your device, so there is no cloud account to create.