Last updated: June 2, 2025
Understanding the UV Index in Boston is crucial for promoting skin health and preventing sunburn, especially during the warm months when UV levels can peak significantly. As a region characterized by a humid subtropical climate, Boston experiences varying UV exposure throughout the year. With UV Index levels reaching as high as 11 during midday, it's vital for residents and visitors alike to stay informed about these fluctuations. By recognizing the potential risks associated with sun exposure, Bostonians can take proactive steps to protect their skin and enjoy the sunshine safely.
At 07:00, the UV Index is a gentle 1, signaling a low level of UV radiation. As the sun climbs, it gradually rises, reaching a moderate 3 by 09:00. The intensity peaks spectacularly at 12:00 with a powerful 10, indicating a high risk of harm from unprotected sun exposure. For those brave enough to venture out, it's crucial to take precautions, especially between 13:00 and 14:00, when it hits its zenith at 11. The afternoon sees a slow decline, tapering down to 5 by 17:00 and further reducing to a mild 2 as evening approaches at 18:00. Finally, the day concludes with the UV Index dropping back to a safe 1 by 19:00, making for a relaxing end to a sun-soaked day.
| 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 | 7 | high | 25 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 | 5 | moderate | 30 min |
| 18:00 | 2 | low | 45 min |
| 19:00 | 1 | low | 45 min |
Throughout the year, UV Index levels fluctuate significantly, with the highest risk observed during the spring and summer months. From February to August, the UV Index remains at a very high to extreme level, peaking at 11 in May, June, July, and August, where the burn time is as short as 10 minutes. Visitors and residents are advised to take extra precautions during these months by wearing protective clothing, applying sunscreen regularly, and seeking shade, especially during midday hours. In contrast, January and December experience moderate UV levels, allowing for longer exposure times of 30 minutes before burning. As the UV levels decline entering the fall months, particularly in November with a high index of 6 (burn time of 25 minutes), it is still prudent to remain vigilant against UV exposure.
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 |
| Boston | 5 | 8 | 9 | 10 | 11 | 11 | 11 | 11 | 10 | 8 | 6 | 4 |
| Houston UVI | 5 | 8 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 9 | 7 | 5 |