weather for boulder.

A chinook is a warm, dry downslope wind that develops on the lee side of mountain ranges when stable air flows over the ridges and descends. As the air sinks down the eastern slope of the Front Range, it warms adiabatically (about 5.5°F per 1,000 feet of descent) and dries dramatically. Boulder can experience chinook events that raise the temperature 30–40°F in a few hours, melting snow within minutes and producing humidity readings in the single digits. The events are most common in winter and early spring.

Boulder sits at the boundary between continental polar air masses descending from Canada and warmer Pacific-modified air pushing east over the Rockies. In spring, when the upper-level pattern produces strong cold-air advection from the north, the polar air can collide with surface moisture from the south and produce rapid snow events. The 2003 Boulder blizzard dropped over 30 inches of snow on the city in 36 hours — a snow event followed days of mild temperatures.

At 5,430 feet of elevation, Boulder receives roughly 25% more UV radiation than sea-level cities at the same latitude. The combination of thin atmosphere (less Rayleigh scattering), low humidity, and clear skies for ~300 days per year produces UV index values in the 9–11+ range from May through September. UV burns happen faster at altitude, and the cumulative dose is meaningful for long-term skin health — a daily concern in the city’s outdoor culture.

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.