Last updated: June 2, 2025
Understanding the UV Index is crucial for anyone exploring the stunning landscapes of Yosemite Valley. This awareness not only helps in preventing sunburn but also plays a vital role in maintaining long-term skin health. With a Csb climate characterized by warm summers and cool winters, Yosemite Valley experiences varying UV levels throughout the day, peaking at a high of 12 around noon. Being informed about these levels empowers visitors to enjoy their adventures safely while minimizing their risk of overexposure to harmful ultraviolet radiation. Whether you're hiking beneath majestic granite cliffs or wandering through lush meadows, knowing the UV Index is an essential part of your outdoor experience.
As the sun rises, the UV Index begins its ascent, starting at a mild 1 at 07:00 and gradually climbing throughout the morning. By 09:00, it reaches a moderate 5, signaling the need for some sun protection. The intensity peaks around 12:00, with a high of 12, which indicates very high levels of UV radiation. Hereafter, the index gently declines, tapering off to 9 by 15:00, before easing down to 4 by 17:00. As the evening unfolds, the UV risk diminishes, dropping to 2 by 18:00 and finally returning to 1 at 19:00. This hourly UVI data underscores the importance of being mindful of sun exposure, especially during the midday hours when UV levels are at their highest.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 2 | low | 45 min |
| 09:00 | 5 | moderate | 30 min |
| 10:00 | 7 | high | 25 min |
| 11:00 | 10 | very high | 15 min |
| 12:00 | 12 | extreme | 10 min |
| 13:00 | 12 | extreme | 10 min |
| 14:00 | 11 | extreme | 10 min |
| 15:00 | 9 | 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 |
Throughout the year, UV Index levels experience significant fluctuations, with the highest risk months occurring from April to August, where the UV Index reaches an extreme level of 12. During these months, the recommended burn time is as brief as 10 minutes, emphasizing the importance of protective measures against harmful UV radiation. Notably, March and September also present very high UV levels of 9 and 10, respectively, with a burn time of 15 minutes. In the winter months (January, November, December), UV exposure is less intense, categorized as moderate to high with burn times ranging from 25 to 30 minutes. Visitors and residents are advised to take extra precautions during high-risk months, such as wearing sunscreen, protective clothing, and seeking shade to minimize sun damage.
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 |
| Yosemite Valley | 4 | 6 | 9 | 11 | 12 | 12 | 12 | 11 | 10 | 7 | 5 | 4 |
| Houston UVI | 5 | 8 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 9 | 7 | 5 |