Newcastle, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.1 °C (low) to 12.9 °C (high). Annual precipitation averages 1265.7 Millimeters. Newcastle is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.4 °C | -0.8 °C | 97.54 mm |
| February | -10.3 °C | 0.9 °C | 89.41 mm |
| March | -5.2 °C | 5.1 °C | 109.22 mm |
| April | 0.4 °C | 11.6 °C | 112.27 mm |
| May | 6.2 °C | 17.7 °C | 96.27 mm |
| June | 11.4 °C | 22.4 °C | 113.28 mm |
| July | 14.8 °C | 25.7 °C | 88.65 mm |
| August | 14.1 °C | 25.3 °C | 81.79 mm |
| September | 10.1 °C | 21.3 °C | 101.85 mm |
| October | 4 °C | 14.6 °C | 136.91 mm |
| November | -1.3 °C | 8.4 °C | 117.09 mm |
| December | -7.2 °C | 2.5 °C | 121.41 mm |
| Annual | 2.1 °C | 12.9 °C | 1265.69 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |