Last updated: June 2, 2025
In Boulder, Colorado, awareness of the UV Index is essential for safeguarding your skin against harmful ultraviolet rays. Understanding UV levels helps in preventing sunburn and maintaining overall skin health, especially because Boulder’s high-altitude climate amplifies UV exposure. With peak UV Index values reaching as high as 11 during midday hours, residents and visitors alike should stay informed and take precautions to protect themselves from the sun's powerful rays. Always remember, whether you're hiking in the picturesque foothills or relaxing outdoors, keeping an eye on the UV Index can make all the difference in your sun safety.
The UV Index shows a dramatic rise as the morning unfolds, starting at a low of 1 at 07:00. By 08:00, it gently climbs to 2, and by 09:00, it reaches 3. The mid-morning reveals a surge, peaking at 5 by 10:00. As the sun reaches its zenith, the UVI soars to a staggering 10 at noon, with a climb to 11 at 13:00, marking the highest point of the day. Just after, it gradually dips, but remains considerable at 10 by 14:00 and 9 at 15:00. The afternoon sees a striking decrease to 7 at 16:00 and continues to fall, landing at 3 by 18:00, before tapering off to 1 by 19:00. It's a clear reminder to stay sun-safe 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 | 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 | 9 | very high | 15 min |
| 16:00 | 7 | high | 25 min |
| 17:00 | 5 | moderate | 30 min |
| 18:00 | 3 | moderate | 30 min |
| 19:00 | 1 | low | 45 min |
Throughout the year, the UV Index experiences significant fluctuations, with the highest risk typically occurring from March to September. Visitors and residents should be particularly cautious during the high-risk months of April (UV Index 8), May (UV Index 9), June (UV Index 11), and July (UV Index 10), where the potential for skin damage is at its peak. During these months, burn times decrease dramatically, with the extreme risk in June allowing for only 10 minutes of unprotected sun exposure. As a guideline, it's advisable to wear protective clothing, apply broad-spectrum sunscreen, and seek shade during peak sun hours to minimize UV exposure. In contrast, October to February sees much lower UV levels, allowing for greater sun safety with recommended burn times ranging from 30 to 45 minutes.
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 |
| Boulder | 3 | 4 | 6 | 8 | 9 | 11 | 10 | 9 | 8 | 5 | 3 | 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 |