About UV Warden
UV Warden shows the daily peak UV index published by the EPA for U.S. ZIP codes and cities, then adds sunrise, sunset and a rough hourly curve so you can plan the day.
Data and method
| Daily peak UV | EPA Envirofacts UV Index forecast, by ZIP code. Fetched when you view a page and cached for up to 30 minutes. |
|---|---|
| Sunrise, sunset, solar noon | Calculated from the city’s latitude and longitude with the standard sunrise equation. Expect accuracy within a few minutes. |
| Hourly bars | An estimate: the EPA peak scaled by the sun’s height at each hour. It is not a measurement or an official hourly forecast. |
| City pages | Each city uses one representative ZIP code, shown in the page’s FAQ. |
What this site is not
It is not affiliated with the EPA, and it is not medical advice. See a clinician about skin concerns.
Last reviewed 2026-10-27.