Altona, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.3 °C (low) to 15.5 °C (high). Annual precipitation averages 984.7 Millimeters. Altona is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.1 °C | -0.9 °C | 42.93 mm |
| February | -8.3 °C | 1.7 °C | 49.78 mm |
| March | -2.4 °C | 8.9 °C | 61.21 mm |
| April | 3.5 °C | 16.3 °C | 99.06 mm |
| May | 10.3 °C | 22.3 °C | 132.33 mm |
| June | 15.7 °C | 27.2 °C | 119.38 mm |
| July | 17.5 °C | 28.9 °C | 99.31 mm |
| August | 16.3 °C | 28 °C | 94.23 mm |
| September | 11.6 °C | 24.8 °C | 97.03 mm |
| October | 5.2 °C | 17.8 °C | 73.15 mm |
| November | -1.2 °C | 9.3 °C | 62.48 mm |
| December | -6.8 °C | 2.2 °C | 53.85 mm |
| Annual | 4.3 °C | 15.5 °C | 984.74 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |