UV Index Today in San Francisco, California
San Francisco's UV Climate
San Francisco is the city where fog and sunburn coexist: Karl the Fog may blanket the Sunset District while the Mission and Dolores Park bake under full sun a few miles east. The city's famous microclimates mean UV exposure varies block by block, and the cool air is a chronic deceiver — temperatures in the 60s convince people they're safe while UV runs high overhead. Cyclists crossing the Golden Gate and picnickers in the sunny eastern neighborhoods burn regularly in this 'cold' city.
Average Annual UV Index
6.5
Peak UV Season
April - September
Sunny Days per Year
259
Typical UV Index by Season in San Francisco
| Season | Typical Midday UV | Protection Needed |
|---|---|---|
| Summer | High to Very High (7-9) | SPF 30+, hat, sunglasses; shade from 10 AM – 4 PM |
| Spring & Fall | Moderate to High (5-8) | SPF 30+ for extended time outdoors |
| Winter | Low to Moderate (2-4) | Sunscreen for long midday exposure; more on snow |
UV Index in Nearby Cities
- UV Index in Palo Alto, CA28 mi away
- UV Index in Santa Clara, CA39 mi away
- UV Index in San Jose, CA42 mi away
- UV Index in Reno, NV186 mi away
Practical Tips for Outdoor Activities
Make the most of outdoor activities while staying safe in San Francisco County:
- Check UV index and weather radar before planning outdoor activities
- Schedule outdoor activities during low UV hours
- Use appropriate sun protection based on UV levels
- Stay hydrated during outdoor activities
- Take regular breaks in shaded areas
- Monitor weather conditions for changes
- Be prepared for sudden weather changes
- Know the signs of heat-related illness
- Wear a hat and protective clothing
- Check visibility conditions before outdoor plans
- Stay alert to weather alerts and warnings
UV and Weather in San Francisco County
Learn about San Francisco County's unique climate patterns, UV radiation levels, and how they affect your daily life. Enter your zip code for location-specific weather radar data and UV forecasts to help you make informed decisions about outdoor activities and sun protection.
Climate and UV Patterns
San Francisco's cool-summer Mediterranean climate produces high UV that rarely feels like it. Clear-day midday values reach 8-9 in summer, and even beneath thin coastal fog a majority of UV gets through — overcast mornings that burn off by noon leave the peak window fully exposed. September and October, the city's true summer, pair the warmest days with still-strong UV, catching residents at Ocean Beach and outdoor festivals.
UV Index and Health Impact
Understanding UV radiation levels is crucial for protecting your health. Typical clear-day UV index values in San Francisco through the year:
- Summer: High to Very High (7-9)
- Spring/Fall: Moderate to High (5-8)
- Winter: Low to Moderate (2-4)
- Peak UV hours: 10 AM - 4 PM
- Cloud cover can reduce UV by 20-40%, but does not eliminate it
- Clear skies bring maximum UV exposure
Local Weather Patterns
The daily fog cycle rules the west side: gray mornings, partial afternoon clearing, fog returning by evening. The eastern and southern neighborhoods — Mission, Potrero, Bernal — sit in a sun belt where UV exposure is dramatically higher than the oceanfront a couple of miles away. Fall's fog-free spells produce the year's clearest skies, and windy conditions at the beaches and headlands mask sun intensity right when reflection off water is adding to it.
Frequently Asked Questions About UV in San Francisco
What is the UV index in San Francisco today?
The live UV index for San Francisco, CA is shown at the top of this page and updates throughout the day, along with today's maximum and an hourly forecast.
When is the sun strongest in San Francisco?
UV radiation is strongest between 10 AM and 4 PM. San Francisco's peak UV season runs April - September, when the midday index typically reaches High to Very High (7-9).
How high does the UV index get in San Francisco?
Summer days in San Francisco typically reach High to Very High (7-9). Spring and fall usually bring Moderate to High (5-8), while winter values are typically Low to Moderate (2-4).
Do I need sunscreen in San Francisco during winter?
San Francisco's clear winter days reach the low-moderate range at midday; sunscreen matters most for long weekend outings, especially in the sunnier eastern neighborhoods.
How sunny is San Francisco compared to other cities?
San Francisco averages about 259 sunny days per year with an average annual UV index around 6.5.