Marshalltown, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.2 °F (low) to 58.4 °F (high). Annual precipitation averages 36.6 Inches. Marshalltown 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 | 10.8 °F | 27.7 °F | 1.03 in. |
| February | 14.6 °F | 32.4 °F | 1.15 in. |
| March | 25.8 °F | 45.4 °F | 2.04 in. |
| April | 37.1 °F | 59.7 °F | 3.8 in. |
| May | 49.6 °F | 70.9 °F | 5.08 in. |
| June | 60.3 °F | 80.6 °F | 5.41 in. |
| July | 63.5 °F | 83.8 °F | 4.29 in. |
| August | 60.7 °F | 81.7 °F | 4.23 in. |
| September | 51.9 °F | 75.8 °F | 3.51 in. |
| October | 39.7 °F | 62.2 °F | 2.61 in. |
| November | 27.6 °F | 46.6 °F | 1.93 in. |
| December | 17.0 °F | 33.4 °F | 1.47 in. |
| Annual | 38.2 °F | 58.4 °F | 36.55 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |