Last updated: July 2, 2025
Understanding the UV Index is essential for residents of Mercer Island, where the unique Csb climate brings varied sun exposure throughout the year. Being aware of UV levels helps prevent sunburn and protects skin health, allowing you to enjoy outdoor activities while minimizing risks. With peak UV levels reaching as high as 9 during midday, it's crucial to stay informed about daily fluctuations, especially when the sun is at its strongest. Equip yourself with this knowledge to safeguard your skin and make the most of Mercer Island's beautiful, sunny days!
As the sun rises, the UV Index begins its journey, starting low at 1 at 07:00 AM and gradually climbing. By 09:00 AM, it hits 3, but the real intensity kicks in by 12:00 PM, peaking at an impressive 8. The UV levels reach their zenith at 1:00 PM and 2:00 PM, where they maintain a high of 9, urging sun-seekers to take precautions. As the afternoon fades, the index gradually declines, dropping to 5 by 4:00 PM and further to 4 at 5:00 PM. As evening approaches, the index settles back down to a gentle 1 by 7:00 PM. It’s a vivid reminder of the sun’s strength—safety and sun protection are key during those peak hours!
| 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 | 5 | moderate | 30 min |
| 11:00 | 7 | high | 25 min |
| 12:00 | 8 | very high | 15 min |
| 13:00 | 9 | very high | 15 min |
| 14:00 | 9 | very high | 15 min |
| 15:00 | 7 | high | 25 min |
| 16:00 | 5 | moderate | 30 min |
| 17:00 | 4 | moderate | 30 min |
| 18:00 | 2 | low | 45 min |
| 19:00 | 1 | low | 45 min |
As the seasons change, so do UV levels, significantly impacting sun exposure and skin safety for visitors and residents. January to March sees a gradual increase in UV Index, peaking with a moderate level in March at 5, where the burn time decreases to 30 minutes. The high-risk months, characterized by extremely high levels of UV radiation, are May through August, with indices soaring to 9 and enforcing a burn time of just 15 minutes. Following this, September presents a moderate risk with an index of 7, and a burn time of 25 minutes, before dropping again in October with a moderate index of 5. November and December then return to lower risks, emphasizing a UV Index of 2 and 1, respectively, allowing for longer safe exposure times of 45 minutes. To minimize the risk of UV-related harm, visitors and residents should take extra precautions during the high-risk months by wearing sunscreen, protective clothing, and limiting sun exposure during peak hours.
UV Risk Categories
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mercer Island | 2 | 3 | 5 | 6 | 8 | 9 | 9 | 8 | 7 | 5 | 2 | 1 |
| 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 |
| Houston UVI | 5 | 8 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 9 | 7 | 5 |