Arnold, Missouri has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.4 °C (low) to 19.3 °C (high). Annual precipitation averages 1125.5 Millimeters. Arnold is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.7 °C | 4.7 °C | 70.1 mm |
| February | -2.8 °C | 7.7 °C | 62.48 mm |
| March | 2.1 °C | 13.3 °C | 92.96 mm |
| April | 8 °C | 20.1 °C | 122.17 mm |
| May | 13.9 °C | 24.9 °C | 132.59 mm |
| June | 18.8 °C | 29.7 °C | 115.82 mm |
| July | 20.9 °C | 31.6 °C | 103.89 mm |
| August | 19.8 °C | 30.8 °C | 91.69 mm |
| September | 15.3 °C | 27.3 °C | 85.6 mm |
| October | 9 °C | 20.8 °C | 84.58 mm |
| November | 2.8 °C | 13.1 °C | 91.95 mm |
| December | -1.9 °C | 7.1 °C | 71.63 mm |
| Annual | 8.4 °C | 19.3 °C | 1125.46 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |