Armstrong, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.3 °C (low) to 13.2 °C (high). Annual precipitation averages 819.7 Millimeters. Armstrong 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 | -13.7 °C | -4.4 °C | 20.07 mm |
| February | -11.6 °C | -2.1 °C | 22.86 mm |
| March | -4.8 °C | 5.1 °C | 44.7 mm |
| April | 1.8 °C | 13.8 °C | 86.11 mm |
| May | 8.8 °C | 20.8 °C | 114.55 mm |
| June | 15 °C | 26.4 °C | 125.73 mm |
| July | 16.8 °C | 28 °C | 103.12 mm |
| August | 15.3 °C | 26.7 °C | 95.25 mm |
| September | 10.6 °C | 23.6 °C | 81.03 mm |
| October | 3.3 °C | 15.7 °C | 60.96 mm |
| November | -3.9 °C | 6.3 °C | 35.31 mm |
| December | -10.2 °C | -1.5 °C | 29.97 mm |
| Annual | 2.3 °C | 13.2 °C | 819.66 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |