Merwin, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7 °C (low) to 18.8 °C (high). Annual precipitation averages 1075.7 Millimeters. Merwin 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 | -6.5 °C | 4.4 °C | 36.58 mm |
| February | -4.5 °C | 6.9 °C | 45.97 mm |
| March | 0.8 °C | 13 °C | 69.09 mm |
| April | 6.4 °C | 18.8 °C | 109.73 mm |
| May | 12.4 °C | 23.9 °C | 151.38 mm |
| June | 17.8 °C | 28.9 °C | 140.21 mm |
| July | 20.2 °C | 31.6 °C | 111.51 mm |
| August | 18.9 °C | 31 °C | 99.57 mm |
| September | 14.1 °C | 26.9 °C | 112.78 mm |
| October | 7.3 °C | 20.3 °C | 87.38 mm |
| November | 1.1 °C | 12.9 °C | 63.25 mm |
| December | -4.2 °C | 6.4 °C | 48.26 mm |
| Annual | 7 °C | 18.8 °C | 1075.71 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |