Monmouth, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.3 °C (low) to 14.6 °C (high). Annual precipitation averages 950.2 Millimeters. Monmouth is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.7 °C | -2.3 °C | 34.04 mm |
| February | -9.7 °C | 0.2 °C | 39.88 mm |
| March | -3.4 °C | 7.5 °C | 56.9 mm |
| April | 2.7 °C | 15.3 °C | 93.47 mm |
| May | 9.3 °C | 21.6 °C | 111.25 mm |
| June | 15 °C | 26.8 °C | 132.33 mm |
| July | 16.8 °C | 28.4 °C | 108.97 mm |
| August | 15.6 °C | 27.5 °C | 106.93 mm |
| September | 10.7 °C | 24.1 °C | 92.2 mm |
| October | 4.2 °C | 16.8 °C | 75.95 mm |
| November | -2.3 °C | 8.2 °C | 54.36 mm |
| December | -8 °C | 0.9 °C | 43.94 mm |
| Annual | 3.3 °C | 14.6 °C | 950.22 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |