Monmouth, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.9 °F (low) to 55.1 °F (high). Annual precipitation averages 47.8 Inches. Monmouth is located in USDA Plant Hardiness Zone 5b. 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 | 10.6 °F | 29.2 °F | 3.53 in. |
| February | 12.3 °F | 32.1 °F | 3.15 in. |
| March | 22.1 °F | 40.4 °F | 3.72 in. |
| April | 33.2 °F | 52.9 °F | 4.26 in. |
| May | 44.0 °F | 64.8 °F | 3.58 in. |
| June | 53.6 °F | 73.5 °F | 4.58 in. |
| July | 59.4 °F | 79.4 °F | 3.63 in. |
| August | 57.9 °F | 78.5 °F | 3.55 in. |
| September | 50.3 °F | 71.0 °F | 3.81 in. |
| October | 39.2 °F | 58.1 °F | 5.34 in. |
| November | 29.3 °F | 46.0 °F | 4.28 in. |
| December | 18.8 °F | 35.3 °F | 4.35 in. |
| Annual | 35.9 °F | 55.1 °F | 47.78 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |