Newcastle, Ontario climate data is summarized below. Average annual temperatures range from 3.9 °C (low) to 12 °C (high). Annual precipitation averages 898 Millimeters. Newcastle is located in USDA Plant Hardiness Zone 6a. 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 | -8.02 °C | -0.91 °C | 30 mm |
| February | -9.35 °C | -1.42 °C | 26 mm |
| March | -3.81 °C | 4.2 °C | 73 mm |
| April | 2.1 °C | 10.48 °C | 110 mm |
| May | 7.66 °C | 16.75 °C | 92 mm |
| June | 13.04 °C | 21.66 °C | 88 mm |
| July | 15.82 °C | 24.81 °C | 91 mm |
| August | 15.6 °C | 24.54 °C | 88 mm |
| September | 11.57 °C | 20.57 °C | 65 mm |
| October | 6.47 °C | 14.06 °C | 81 mm |
| November | 0.63 °C | 7.79 °C | 78 mm |
| December | -4.37 °C | 1.71 °C | 76 mm |
| Annual | 3.9 °C | 12 °C | 898 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |