UV index in San Francisco
The UV index measures the sun's ultraviolet strength on a 0-11+ scale. Protection is recommended once it reaches 3 — in much of the US that is most midday hours from spring through early fall.
☀️ Right now
036811+
Guidance:
No protection needed for most people.
UV across the country today
The strongest sun among the cities we track today is over San Antonio, TX, where the index peaks near 5. None of them reach the very-high band today. The index tracks the sun's angle, not the heat: it peaks within an hour of solar noon, runs higher at altitude and roughly doubles off snow or water.