Last updated: July 2, 2025
Understanding the UV Index is crucial for anyone enjoying the breathtaking beauty of Yosemite Valley. With its stunning landscapes and high elevation, this iconic destination experiences significant UV exposure, especially during summer months. Monitoring UV levels helps you take necessary precautions against sunburn and long-term skin damage, ensuring you can fully enjoy your outdoor adventures. Typical midday readings can reach a high of 12, indicating intense UV radiation that can lead to skin health risks if not managed properly. Stay informed to protect yourself and bask in the beauty of Yosemite Valley safely!
The UV Index throughout the day reveals an intensely radiant midday peak, starting gently at 1 by 7 AM. As the sun ascends, the index escalates, reaching 4 by 9 AM, before dramatically soaring to a maximum of 12 between noon and 1 PM. This indicates high UV exposure, necessitating protective measures for outdoor enthusiasts. Gradually, the index dips to 9 by 3 PM, showcasing a fading intensity as dusk approaches. By the late afternoon, it continues its descent to 1 by 7 PM, marking a significant drop in UV radiation levels. This data emphasizes the importance of being vigilant during peak hours when the sun's rays are most potent.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 2 | low | 45 min |
| 09:00 | 4 | 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 | 7 | 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 |