Oswego, Kansas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.4 °C (low) to 19.9 °C (high). Annual precipitation averages 1170.4 Millimeters. Oswego 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 | -4.6 °C | 6.4 °C | 42.93 mm |
| February | -2.4 °C | 9.2 °C | 46.48 mm |
| March | 2.4 °C | 14.6 °C | 81.28 mm |
| April | 7.7 °C | 19.9 °C | 125.22 mm |
| May | 13.6 °C | 24.4 °C | 179.83 mm |
| June | 18.7 °C | 29.4 °C | 141.48 mm |
| July | 21 °C | 31.9 °C | 104.14 mm |
| August | 19.9 °C | 31.9 °C | 100.84 mm |
| September | 15.3 °C | 27.4 °C | 115.57 mm |
| October | 8.7 °C | 21.3 °C | 99.06 mm |
| November | 2.4 °C | 14.2 °C | 73.91 mm |
| December | -2.4 °C | 8.2 °C | 59.69 mm |
| Annual | 8.4 °C | 19.9 °C | 1170.43 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |