Last updated: July 2, 2025
In Sunnyvale, United States, being aware of the UV Index is crucial for protecting your skin from harmful rays. Understanding UV levels can significantly reduce the risk of sunburn and long-term skin damage, making it an essential consideration for residents and visitors alike. With Sunnyvale’s Cfa climate—known for its warm summers and mild winters—UV exposure can peak dramatically, particularly during midday hours when the index reaches a maximum of 11. By staying informed about UV levels throughout the day, you can enjoy the sun safely while prioritizing your skin health.
The UV Index for the day showcases a dramatic increase in intensity as the sun climbs higher in the sky. Starting at a mild 1 at 07:00, it remains low throughout the morning, only reaching 3 by 09:00. However, by 11:00, the index skyrockets to 8, peaking at an intense 11 from 13:00 to 14:00. As the afternoon wanes, the UV levels gradually decrease, dropping to 4 by 17:00 and tapering off to 1 once again by 19:00. It's clear that midday hours pose the greatest risk for sun exposure, making it crucial to take precautions during the peak hours from 11:00 to 14:00.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 1 | low | 45 min |
| 09:00 | 3 | moderate | 30 min |
| 10:00 | 5 | moderate | 30 min |
| 11:00 | 8 | very high | 15 min |
| 12:00 | 10 | very high | 15 min |
| 13:00 | 11 | extreme | 10 min |
| 14:00 | 11 | extreme | 10 min |
| 15:00 | 10 | very high | 15 min |
| 16:00 | 7 | high | 25 min |
| 17:00 | 4 | moderate | 30 min |
| 18:00 | 2 | low | 45 min |
| 19:00 | 1 | low | 45 min |
Throughout the year, the UV Index shows significant seasonal changes, particularly peaking during the summer months. From January to February, the UV Index rises from a moderate level of 4 to a high 7, indicating the need for increased sun protection. The months of March through August are notably high-risk, as the UV Index remains in the very high to extreme category, reaching a peak of 11 in May through August, with a burn time of only 10 minutes; therefore, individuals should practice stringent sun safety, including wearing protective clothing and using sunscreen frequently. As we move into September and October, the UV Index decreases but remains a concern, especially in September with a UV of 10. By November and December, the levels drop back to moderate (4) and high (6), allowing for a temporary respite. Visitors and residents should remain vigilant during the high-risk months and adopt protective measures against harmful UV exposure, particularly from March through October.
UV Risk Categories
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chicago UVI | 3 | 4 | 6 | 8 | 9 | 10 | 10 | 9 | 8 | 6 | 4 | 2 |
| Brooklyn UVI | 3 | 5 | 6 | 8 | 10 | 10 | 9 | 9 | 8 | 6 | 4 | 2 |
| New York City UVI | 3 | 5 | 6 | 8 | 10 | 10 | 9 | 9 | 8 | 6 | 4 | 2 |
| Los Angeles UVI | 4 | 6 | 8 | 9 | 10 | 11 | 11 | 10 | 10 | 7 | 5 | 4 |
| Sunnyvale | 4 | 7 | 8 | 10 | 11 | 11 | 11 | 11 | 10 | 8 | 6 | 4 |
| Houston UVI | 5 | 8 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 9 | 7 | 5 |