Calmar, Iowa has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2 °C (low) to 12.9 °C (high). Annual precipitation averages 958.3 Millimeters. Calmar 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 | -13.6 °C | -4.3 °C | 26.42 mm |
| February | -11.7 °C | -1.9 °C | 28.19 mm |
| March | -5 °C | 5.3 °C | 50.04 mm |
| April | 1.5 °C | 13.6 °C | 100.33 mm |
| May | 8.2 °C | 20.1 °C | 120.65 mm |
| June | 14.3 °C | 25.3 °C | 155.45 mm |
| July | 16.1 °C | 27.1 °C | 117.6 mm |
| August | 14.6 °C | 26.1 °C | 108.46 mm |
| September | 10 °C | 22.6 °C | 96.01 mm |
| October | 3.1 °C | 15.3 °C | 71.37 mm |
| November | -3.4 °C | 6.2 °C | 47.5 mm |
| December | -9.8 °C | -1.1 °C | 36.32 mm |
| Annual | 2 °C | 12.9 °C | 958.34 mm |
| 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 : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |