Thunder Bay, Ontario climate data is summarized below. Average annual temperatures range from -1.6 °C (low) to 8.9 °C (high). Annual precipitation averages 546 Millimeters. Thunder Bay is located in USDA Plant Hardiness Zone 3b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -17.61 °C | -7.99 °C | 0 mm |
| February | -17.61 °C | -6.25 °C | 0 mm |
| March | -9.63 °C | 1.58 °C | 0 mm |
| April | -2.66 °C | 8.18 °C | 27 mm |
| May | 3.56 °C | 14.93 °C | 91 mm |
| June | 9.07 °C | 20.45 °C | 91 mm |
| July | 12.59 °C | 24.19 °C | 94 mm |
| August | 12.05 °C | 24.04 °C | 74 mm |
| September | 7.23 °C | 18.8 °C | 72 mm |
| October | 2.15 °C | 11.02 °C | 67 mm |
| November | -4.72 °C | 3.31 °C | 30 mm |
| December | -14.14 °C | -5.57 °C | 0 mm |
| Annual | -1.6 °C | 8.9 °C | 546 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 3b : -37.2°C to -34.4°C |
| Current Drought Conditions | Normal |