UV Index
UV Index
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Today's UV index in San Francisco, United States 
will be up to 6.1, indicating high risk of harm from the sun's UV rays for the average person. Check our tips for today to make sure you're safe in the sun.
With San Francisco's UV index reaching 6.1, protect your skin from harm by staying in shade, wearing protective clothing, and applying SPF 30+ sunscreen every 2 hours between 10 a.m. and 4 p.m., when UV rays are strongest.
Read more here about the climate and sun exposure in and around San Francisco.
The UV index in San Francisco usually ranges from moderate to high. During summer, when the sun is strongest, the UV index can reach levels of 8 or 9 (very high), meaning it takes around 15-20 minutes to get a sunburn if not properly protected. In winter, the UV index is lower, around 3-4 (moderate), which means it takes around 30-45 minutes to get a sunburn.
San Francisco experiences a mild and temperate climate throughout the year. Summers are usually cool and foggy due to the city's proximity to the cold California Current. Average temperatures range from 13-24 °C (55-75 °F) in summer and 7-14 °C (45-58 °F) in winter. The city's microclimates can bring temperature variations across different neighborhoods or even within the same area.
Compared to other regions in California, San Francisco has a cooler and foggier climate thanks to the cold ocean current. This results in fewer sunny days per year, averaging around 260-290 days, compared to California's inland areas that enjoy more sunlight. It's important to take sun protection measures even on cloudy days because the UV rays can still reach the skin and cause damage.
The chart above displays the Shortwave Radiation Sum (MJ/m²) for each day of the last year in San Francisco. It's designed to provide you with a better understanding of the yearly weather and sun exposure.