Last updated: May 3, 2025
Understanding the UV Index is crucial for residents and visitors in Guerneville, United States, where the beautiful scenery comes with a unique sun exposure challenge. With typical Csb climate conditions, the UV levels can soar—reaching a peak index of 10 during midday hours. Awareness of these levels is essential for preventing sunburn and protecting skin health. By keeping an eye on the UV Index, you can enjoy the sun safely while ensuring you're taking the necessary precautions to shield yourself from potential damage.
As the sun rises, the UV Index begins its gradual ascent, starting at a mild 1 at 07:00. By 08:00, it reaches 2, indicating a low risk, perfect for morning strolls. The intensity picks up at 09:00, hitting 3, and then surges to 6 by 10:00. From 11:00 to 13:00, the index escalates dramatically, peaking at an intense 10, marking the hours when sun protection is crucial. The afternoon maintains this peak, with 10 persisting until 14:00. As the day progresses, the evening brings relief; the index drops to 8 at 15:00, and gradually declines to 3 by 17:00, and finally retreats to 1 by 19:00. This hourly data highlights the importance of seeking shade and using sunscreen during midday hours to ensure safety under the sun.
| 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 | 10 | very high | 15 min |
| 14:00 | 10 | very high | 15 min |
| 15:00 | 8 | very high | 15 min |
| 16:00 | 6 | high | 25 min |
| 17:00 | 3 | moderate | 30 min |
| 18:00 | 2 | low | 45 min |
| 19:00 | 1 | low | 45 min |
As the seasons change, so does the UV Index, reflecting the risk of UV exposure throughout the year. January and December see a moderate UV Index of 3, allowing for a burn time of 30 minutes. However, from February to March, the UV levels rise significantly, peaking at 11 during the summer months of June and July, categorized as extreme, with the shortest burn time of only 10 minutes in peak months like June. The high-risk months for UV exposure are clearly April to August, when the UV Index reaches very high to extreme levels. It is advisable for visitors and residents to take necessary precautions, such as wearing sunscreen, protective clothing, and limiting sun exposure during peak hours, especially from late spring to mid-summer. As fall approaches, the risk decreases, with the UV Index dropping back to moderate levels by November.
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 |
| Guerneville | 3 | 5 | 7 | 8 | 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 |