Old Washington, Ohio has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.1 °C (low) to 16.4 °C (high). Annual precipitation averages 1043.2 Millimeters. Old Washington is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.7 °C | 2.5 °C | 78.49 mm |
| February | -5.7 °C | 4.4 °C | 58.17 mm |
| March | -1.6 °C | 9.8 °C | 86.36 mm |
| April | 4.2 °C | 17.2 °C | 94.74 mm |
| May | 9.8 °C | 22.2 °C | 101.85 mm |
| June | 14.7 °C | 26.4 °C | 120.4 mm |
| July | 16.9 °C | 28.4 °C | 102.62 mm |
| August | 15.8 °C | 27.8 °C | 92.2 mm |
| September | 11.8 °C | 24.4 °C | 85.85 mm |
| October | 5.6 °C | 17.9 °C | 72.39 mm |
| November | 0.3 °C | 11.2 °C | 74.93 mm |
| December | -3.6 °C | 5.1 °C | 75.18 mm |
| Annual | 5.1 °C | 16.4 °C | 1043.18 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 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 |