Altamont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 44 °F (low) to 64.4 °F (high). Annual precipitation averages 43.3 Inches. Altamont is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 20.8 °F | 37.0 °F | 2.91 in. |
| February | 24.0 °F | 41.9 °F | 2.4 in. |
| March | 33.0 °F | 52.8 °F | 3.21 in. |
| April | 43.2 °F | 65.3 °F | 4.72 in. |
| May | 54.1 °F | 75.1 °F | 4.87 in. |
| June | 63.1 °F | 84.1 °F | 4.83 in. |
| July | 66.1 °F | 87.3 °F | 4.18 in. |
| August | 63.7 °F | 86.1 °F | 3.16 in. |
| September | 55.6 °F | 80.3 °F | 3.12 in. |
| October | 44.3 °F | 68.1 °F | 3.45 in. |
| November | 34.0 °F | 53.3 °F | 3.69 in. |
| December | 25.8 °F | 41.6 °F | 2.8 in. |
| Annual | 44 °F | 64.4 °F | 43.34 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |