Onslow, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 37.1 °F (low) to 57.6 °F (high). Annual precipitation averages 38.3 Inches. Onslow is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 10.1 °F | 27.2 °F | 1.31 in. |
| February | 13.8 °F | 31.6 °F | 1.54 in. |
| March | 25.3 °F | 44.8 °F | 2.27 in. |
| April | 36.2 °F | 59.0 °F | 3.78 in. |
| May | 47.9 °F | 70.2 °F | 4.48 in. |
| June | 58.3 °F | 79.6 °F | 5.44 in. |
| July | 61.6 °F | 82.6 °F | 4.52 in. |
| August | 59.2 °F | 80.9 °F | 4.33 in. |
| September | 50.4 °F | 74.5 °F | 3.65 in. |
| October | 38.7 °F | 61.6 °F | 3.05 in. |
| November | 27.1 °F | 45.9 °F | 2.23 in. |
| December | 16.8 °F | 32.9 °F | 1.73 in. |
| Annual | 37.1 °F | 57.6 °F | 38.33 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |