Last updated: June 2, 2025
Understanding the UV Index is crucial for residents of Mill Valley, California, where the stunning natural beauty comes with the responsibility of protecting our skin from harmful UV rays. With a typical Mediterranean climate (Csb), Mill Valley experiences significant sun exposure, particularly during the midday hours when UV levels peak. By staying informed about local UV levels, you can take proactive measures against sunburn and long-term skin damage, ensuring that your outdoor adventures are both enjoyable and safe. As the UV Index climbs to 11 around noon, awareness becomes your best defense against the risks associated with high sun exposure in this picturesque region.
The UV Index paints a vivid picture of sun intensity throughout the day. Starting off at a low 1 at 7:00 AM, the sun begins to rise, prompting a gradual increase as it climbs higher in the sky. By 9:00 AM, the index reaches 4, indicating moderate exposure. The intensity peaks sharply at 12:00 PM with a notable 10 and hits its zenith at 1:00 PM, boasting an impressive 11. As the afternoon wears on, this extreme UV exposure begins to taper off, dropping to 9 by 3:00 PM and then descending further to 2 by 6:00 PM. Finally, as twilight approaches, the index falls back to a gentle 1 by 7:00 PM. It’s a vivid reminder of the sun’s power, urging us to take precautions during those peak hours!
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 2 | low | 45 min |
| 09:00 | 4 | moderate | 30 min |
| 10:00 | 6 | high | 25 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 | 9 | very high | 15 min |
| 16:00 | 6 | high | 25 min |
| 17:00 | 4 | moderate | 30 min |
| 18:00 | 2 | low | 45 min |
| 19:00 | 1 | low | 45 min |
The UV Index exhibits significant seasonal variation, peaking during the summer months and dramatically declining in winter. From January to February, the UV Index ranges from 3 to 5, classified as moderate, allowing for around 30 minutes of safe sun exposure. However, March to June sees a sharp increase, reaching an extreme level of 11 in both June and July, where unprotected skin can burn in just 10 minutes. The high-risk months for UV exposure are therefore March through August, where the index remains predominantly high to extreme. As a result, it is crucial for visitors and residents to take protective measures during these months, such as wearing sunscreen, protective clothing, and seeking shade, especially during peak hours. From September to December, while the UV Index decreases, users should still remain vigilant, as moderate levels persist late in the year.
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 |
| Mill Valley | 3 | 5 | 8 | 9 | 10 | 11 | 11 | 10 | 9 | 6 | 4 | 3 |
| Los Angeles UVI | 4 | 6 | 8 | 9 | 10 | 11 | 11 | 10 | 10 | 7 | 5 | 4 |
| Houston UVI | 5 | 8 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 9 | 7 | 5 |