Ayer, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 38.2 °F (low) to 59.8 °F (high). Annual precipitation averages 48.3 Inches. Ayer 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. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.1 °F | 34.4 °F | 3.55 in. |
| February | 16.9 °F | 37.3 °F | 3.37 in. |
| March | 24.9 °F | 45.1 °F | 4.28 in. |
| April | 35.5 °F | 58.4 °F | 4.0 in. |
| May | 46.2 °F | 69.3 °F | 3.74 in. |
| June | 55.7 °F | 78.1 °F | 4.51 in. |
| July | 61.4 °F | 83.9 °F | 3.72 in. |
| August | 59.8 °F | 82.3 °F | 3.94 in. |
| September | 51.6 °F | 75.0 °F | 4.0 in. |
| October | 39.8 °F | 62.4 °F | 4.84 in. |
| November | 30.3 °F | 50.7 °F | 3.86 in. |
| December | 21.7 °F | 40.1 °F | 4.48 in. |
| Annual | 38.2 °F | 59.8 °F | 48.29 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |