Chelmsford, Ontario climate data is summarized below. Average annual temperatures range from -1.3 °C (low) to 10.2 °C (high). Annual precipitation averages 605 Millimeters. Chelmsford is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -16.8 °C | -6.53 °C | 0 mm |
| February | -17.4 °C | -5.75 °C | 0 mm |
| March | -10.34 °C | 1.67 °C | 13 mm |
| April | -2.17 °C | 9.82 °C | 60 mm |
| May | 4.95 °C | 18.54 °C | 71 mm |
| June | 10.32 °C | 23.28 °C | 69 mm |
| July | 12.28 °C | 25.41 °C | 74 mm |
| August | 11.66 °C | 24.2 °C | 89 mm |
| September | 6.86 °C | 19.38 °C | 81 mm |
| October | 1.69 °C | 11.66 °C | 101 mm |
| November | -4.2 °C | 4.33 °C | 46 mm |
| December | -12.03 °C | -3.46 °C | 1 mm |
| Annual | -1.3 °C | 10.2 °C | 605 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |