Eureka, Missouri has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 7.5 °C (low) to 19 °C (high). Annual precipitation averages 1114.8 Millimeters. Eureka 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. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.7 °C | 4.2 °C | 70.36 mm |
| February | -3.7 °C | 7.4 °C | 60.96 mm |
| March | 1.2 °C | 13 °C | 93.47 mm |
| April | 7.1 °C | 19.8 °C | 120.9 mm |
| May | 13.1 °C | 24.7 °C | 131.83 mm |
| June | 18.1 °C | 29.3 °C | 114.05 mm |
| July | 20.3 °C | 31.4 °C | 101.09 mm |
| August | 19.1 °C | 30.7 °C | 92.2 mm |
| September | 14.3 °C | 27.1 °C | 86.61 mm |
| October | 7.6 °C | 20.6 °C | 84.58 mm |
| November | 1.6 °C | 13.1 °C | 90.17 mm |
| December | -3.2 °C | 6.8 °C | 68.58 mm |
| Annual | 7.5 °C | 19 °C | 1114.8 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 6b : -20.6°C to -17.8°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 |