Last updated: July 2, 2025
In Tamalpais-Homestead Valley, staying informed about the UV Index is crucial for protecting your skin and maintaining overall health. Understanding UV levels not only helps prevent painful sunburns but also plays a vital role in reducing long-term skin damage and the risk of skin cancer. With its Csb climate, this picturesque region experiences distinct seasonal variations, leading to fluctuating UV exposure risks throughout the year. During peak hours, especially between 10 AM and 2 PM, UV Index values can soar to 10 and 11, indicating a very high risk of harm from unprotected sun exposure. Being aware of these levels allows residents and visitors alike to enjoy the great outdoors while taking the necessary precautions for their skin's safety.
As the sun rises, the UV Index starts off gently at 1 by 7:00 AM, gradually climbing as the day progresses. By 10:00 AM, it reaches 6, signaling a notable increase in solar radiation. The intensity peaks at 12:00 PM with a striking 10 and continues to soar to a maximum of 11 at 1:00 PM, marking the hour of greatest exposure. As the afternoon unfolds, the index begins to taper off—dropping to 10 at 2:00 PM and 8 by 3:00 PM. By late afternoon, the UV Index gracefully descends to 4 at 5:00 PM, settling back to 2 by 6:00 PM and finally returning to a gentle 1 by 7:00 PM. This highlights the importance of sun protection during mid-day when UV rays are at their most intense.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 2 | low | 45 min |
| 09:00 | 3 | 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 | 10 | very high | 15 min |
| 15:00 | 8 | 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 |
| Tamalpais-Homestead 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 |