Last updated: July 2, 2025
Understanding the UV Index in Greybull, United States, is crucial for protecting your skin and overall health. As the sun's rays can be particularly intense here, especially during peak hours when indices soar to 11, being aware of UV levels helps you take proactive measures against sunburn and long-term skin damage. This high desert climate, characterized by its BWk classification, brings unique exposure risks, making it even more important to stay informed about daily UV variations. Whether you’re planning outdoor activities or just enjoying a sunny day, knowing the UV Index is key to ensuring your safety under the sun.
At dawn, the UV Index starts off gentle, peaking at 1 by 7:00 AM. As the sun climbs higher, the index rises steadily, hitting 2 by 8:00 AM, then surging to 4 at 9:00 AM. The intensity escalates, reaching a robust 6 by 10:00 AM, and striking its peak at 10 by noon. The highest values occur between 1:00 PM and 2:00 PM, where it boldly stands at 11. As the afternoon progresses, the index begins to wane, falling to 9 at 3:00 PM, then dropping further to 7 by 4:00 PM. By 5:00 PM, the UV Index returns to a more manageable 4, before tapering off to 2 at 6:00 PM and concluding at 1 by 7:00 PM. It's essential to stay protected during those peak hours for safe sun exposure!
| 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 | 6 | high | 25 min |
| 11:00 | 8 | very high | 15 min |
| 12:00 | 10 | very high | 15 min |
| 13:00 | 11 | 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, ultraviolet (UV) radiation levels fluctuate significantly, impacting the risk of sunburn and skin damage. Higher UV Index values are observed from March to September, with the highest risks occurring in June and July (UV Index 11, extreme), where the recommended burn time is just 10 minutes. As spring transitions into summer, the UV Index escalates from a moderate level of 3 in January to very high levels of 8 in April and 10 in May. Visitors and residents are strongly advised to take precautions during these high-risk months, particularly from April through August, by using sunscreen, wearing protective clothing, and seeking shade during peak hours. In contrast, the UV Index decreases in the fall and winter, dropping to a low of 2 in December, where the burn time extends to 45 minutes. Remaining aware of these seasonal changes is essential for maintaining skin health year-round.
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 |
| Greybull | 3 | 5 | 6 | 8 | 10 | 11 | 11 | 10 | 9 | 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 |