Washington, Oklahoma has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.4 °C (low) to 22.9 °C (high). Annual precipitation averages 955.8 Millimeters. Washington is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -2.9 °C | 10.6 °C | 36.58 mm |
| February | -0.8 °C | 13.1 °C | 44.7 mm |
| March | 4.1 °C | 18.1 °C | 68.83 mm |
| April | 8.7 °C | 22.7 °C | 96.27 mm |
| May | 14.4 °C | 26.7 °C | 139.45 mm |
| June | 19.3 °C | 31.4 °C | 111.51 mm |
| July | 21.4 °C | 34.5 °C | 84.84 mm |
| August | 20.7 °C | 34.5 °C | 74.93 mm |
| September | 16.3 °C | 30.1 °C | 101.85 mm |
| October | 9.7 °C | 23.9 °C | 89.15 mm |
| November | 3.5 °C | 17.2 °C | 54.1 mm |
| December | -1.4 °C | 11.4 °C | 53.59 mm |
| Annual | 9.4 °C | 22.9 °C | 955.8 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |