Callao, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.8 °C (low) to 17.5 °C (high). Annual precipitation averages 1058.2 Millimeters. Callao is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.2 °C | 1.9 °C | 40.64 mm |
| February | -6.2 °C | 4.9 °C | 49.53 mm |
| March | -0.6 °C | 11.4 °C | 67.82 mm |
| April | 5.4 °C | 17.9 °C | 108.71 mm |
| May | 11.5 °C | 23.3 °C | 139.7 mm |
| June | 16.8 °C | 28.2 °C | 141.22 mm |
| July | 19.1 °C | 30.7 °C | 114.55 mm |
| August | 17.7 °C | 30.2 °C | 99.31 mm |
| September | 12.8 °C | 26.1 °C | 102.36 mm |
| October | 6.4 °C | 19.3 °C | 84.33 mm |
| November | 0.2 °C | 11.4 °C | 64.01 mm |
| December | -5.3 °C | 4.4 °C | 45.97 mm |
| Annual | 5.8 °C | 17.5 °C | 1058.15 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |