Sarnia, Ontario climate data is summarized below. Average annual temperatures range from 39.9 °F (low) to 55.9 °F (high). Annual precipitation averages 6.4 Inches. Sarnia is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -22.2 °F | -18.3 °F | 127 in. |
| February | -22.6 °F | -18.5 °F | 0 in. |
| March | -19.4 °F | -14.6 °F | 203.2 in. |
| April | -16.5 °F | -10.9 °F | 406.4 in. |
| May | -13.3 °F | -7.3 °F | 635 in. |
| June | -10.3 °F | -4.4 °F | 558.8 in. |
| July | -8.7 °F | -3.1 °F | 660.4 in. |
| August | -8.9 °F | -3.4 °F | 660.4 in. |
| September | -11.2 °F | -5.6 °F | 381 in. |
| October | -13.9 °F | -9.2 °F | 254 in. |
| November | -17.2 °F | -13 °F | 228.6 in. |
| December | -19.8 °F | -16.6 °F | 50.8 in. |
| Annual | 39.9 °F | 55.9 °F | 6.44 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Normal |