Bethalto, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 46.3 °F (low) to 65.1 °F (high). Annual precipitation averages 43.5 Inches. Bethalto 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 Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 22.7 °F | 38.6 °F | 2.61 in. |
| February | 26.1 °F | 44.0 °F | 2.35 in. |
| March | 34.9 °F | 54.2 °F | 3.38 in. |
| April | 45.6 °F | 65.9 °F | 4.82 in. |
| May | 56.5 °F | 75.2 °F | 5.18 in. |
| June | 65.4 °F | 83.9 °F | 4.52 in. |
| July | 69.0 °F | 86.8 °F | 4.15 in. |
| August | 67.0 °F | 86.0 °F | 3.77 in. |
| September | 58.6 °F | 80.1 °F | 3.22 in. |
| October | 47.0 °F | 68.3 °F | 3.31 in. |
| November | 36.0 °F | 54.4 °F | 3.52 in. |
| December | 27.3 °F | 43.3 °F | 2.67 in. |
| Annual | 46.3 °F | 65.1 °F | 43.5 in. |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 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 |