Griswold, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4 °C (low) to 16 °C (high). Annual precipitation averages 888.7 Millimeters. Griswold is located in USDA Plant Hardiness Zone 5b. 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 | -10.9 °C | -0.4 °C | 21.08 mm |
| February | -8.7 °C | 2.3 °C | 27.94 mm |
| March | -2.5 °C | 9.7 °C | 48.51 mm |
| April | 3.3 °C | 16.8 °C | 88.9 mm |
| May | 10.2 °C | 22.5 °C | 138.68 mm |
| June | 16.1 °C | 27.8 °C | 130.05 mm |
| July | 18.2 °C | 29.7 °C | 99.06 mm |
| August | 16.7 °C | 28.8 °C | 99.82 mm |
| September | 11.3 °C | 25.3 °C | 85.85 mm |
| October | 4.6 °C | 18.3 °C | 72.39 mm |
| November | -2.4 °C | 9.4 °C | 43.18 mm |
| December | -7.9 °C | 2.3 °C | 33.27 mm |
| Annual | 4 °C | 16 °C | 888.73 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 5b : -26.1°C to -23.3°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 |