Plymouth, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 35.9 °F (low) to 55.4 °F (high). Annual precipitation averages 36.4 Inches. Plymouth 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.2 °F | 23.9 °F | 0.96 in. |
| February | 11.2 °F | 28.5 °F | 1.1 in. |
| March | 23.4 °F | 41.0 °F | 1.98 in. |
| April | 35.1 °F | 56.5 °F | 3.92 in. |
| May | 47.4 °F | 68.6 °F | 5.22 in. |
| June | 58.0 °F | 78.7 °F | 5.5 in. |
| July | 61.6 °F | 81.8 °F | 4.62 in. |
| August | 58.9 °F | 79.5 °F | 3.96 in. |
| September | 50.2 °F | 73.4 °F | 3.41 in. |
| October | 37.7 °F | 59.9 °F | 2.61 in. |
| November | 25.4 °F | 43.4 °F | 1.74 in. |
| December | 14.2 °F | 29.7 °F | 1.33 in. |
| Annual | 35.9 °F | 55.4 °F | 36.35 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |