St Thomas, Ontario climate data is summarized below. Average annual temperatures range from 4.5 °C (low) to 13.8 °C (high). Annual precipitation averages 511 Millimeters. St Thomas is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.72 °C | -0.66 °C | 11 mm |
| February | -9.33 °C | -1.21 °C | 1 mm |
| March | -3.17 °C | 5.81 °C | 27 mm |
| April | 2.65 °C | 13.16 °C | 37 mm |
| May | 8.63 °C | 19.96 °C | 56 mm |
| June | 13.84 °C | 24.84 °C | 70 mm |
| July | 16.39 °C | 27.16 °C | 86 mm |
| August | 15.86 °C | 26.45 °C | 85 mm |
| September | 11.84 °C | 22.5 °C | 62 mm |
| October | 6.61 °C | 15.63 °C | 39 mm |
| November | 1.18 °C | 8.86 °C | 23 mm |
| December | -3.27 °C | 2.52 °C | 14 mm |
| Annual | 4.5 °C | 13.8 °C | 511 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |