Calais, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.9 °C (low) to 12.4 °C (high). Annual precipitation averages 1208.3 Millimeters. Calais is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -12.9 °C | -2.1 °C | 103.12 mm |
| February | -12.3 °C | -0.4 °C | 82.55 mm |
| March | -6.7 °C | 4.2 °C | 100.58 mm |
| April | -0.4 °C | 10.7 °C | 94.49 mm |
| May | 5.1 °C | 17.3 °C | 96.27 mm |
| June | 10.3 °C | 22.6 °C | 93.73 mm |
| July | 13.6 °C | 25.9 °C | 86.61 mm |
| August | 12.6 °C | 25.7 °C | 83.57 mm |
| September | 8.6 °C | 21.4 °C | 89.92 mm |
| October | 3.1 °C | 14.4 °C | 132.08 mm |
| November | -1.8 °C | 7.7 °C | 121.92 mm |
| December | -8.2 °C | 1.4 °C | 123.44 mm |
| Annual | 0.9 °C | 12.4 °C | 1208.28 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |