Last updated: July 2, 2025
Understanding the UV Index in Thunder Bay, Canada is essential for safeguarding your skin against harmful UV radiation. With summer days frequently bringing elevated UV levels, awareness can help you prevent sunburn and long-term skin damage. Thunder Bay's Dfb climate often features clear skies and reflective surfaces like water and snow, which can amplify UV exposure, particularly during peak hours when the index reaches as high as 8 between 1 PM and 3 PM. Staying informed about the UV Index is a simple yet powerful way to protect your skin and enjoy the beautiful outdoors safely.
The UV Index rises dramatically as the day unfolds, starting with a mild 1 at 07:00 and escalating to a peak of 8 between 13:00 and 15:00. This midday sun intensity signals a critical time for sun protection, with optimal caution advised given the 7 at 12:00 and the 8 that follows. As the afternoon wanes, the index gradually declines, dropping to 5 by 17:00 and tapering to below 3 by 19:00. It's a day characterized by a significant UV presence, underscoring the importance of vigilance in sun safety during those peak afternoon hours.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 1 | low | 45 min |
| 09:00 | 2 | low | 45 min |
| 10:00 | 3 | moderate | 30 min |
| 11:00 | 5 | moderate | 30 min |
| 12:00 | 7 | high | 25 min |
| 13:00 | 8 | very high | 15 min |
| 14:00 | 8 | very high | 15 min |
| 15:00 | 8 | very high | 15 min |
| 16:00 | 7 | high | 25 min |
| 17:00 | 5 | moderate | 30 min |
| 18:00 | 3 | moderate | 30 min |
| 19:00 | 2 | low | 45 min |
Throughout the year, UV exposure varies significantly, with key changes occurring as seasons shift. The high-risk months for UV exposure are from April to August, where the UV Index reaches very high levels (8-9) in May, June, July, and August, with a burn time as brief as 15 minutes. As summer transitions into fall, UV levels decrease, dropping to moderate categories in October and low levels during the winter months of November and December. Visitors and residents are advised to take extra precautions during the high-risk months by wearing protective clothing, applying sunscreen frequently, and seeking shade to minimize the risk of UV-related harm.
UV Risk Categories
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Edmonton UVI | 2 | 3 | 5 | 6 | 7 | 7 | 8 | 7 | 6 | 4 | 2 | 1 |
| Calgary UVI | 2 | 3 | 4 | 6 | 8 | 8 | 9 | 8 | 7 | 4 | 2 | 1 |
| Thunder Bay | 2 | 3 | 5 | 7 | 8 | 9 | 8 | 8 | 7 | 4 | 2 | 1 |
| Montreal UVI | 2 | 4 | 5 | 7 | 9 | 9 | 8 | 8 | 7 | 5 | 3 | 2 |
| Ottawa UVI | 2 | 4 | 5 | 8 | 9 | 9 | 8 | 8 | 7 | 5 | 3 | 2 |
| Toronto UVI | 2 | 4 | 5 | 8 | 9 | 9 | 9 | 9 | 7 | 5 | 3 | 2 |