Stanley, Iowa has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.2 °F (low) to 56.4 °F (high). Annual precipitation averages 37.3 Inches. Stanley is located in USDA Plant Hardiness Zone 4b. 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 | 8.0 °F | 25.4 °F | 1.11 in. |
| February | 11.9 °F | 29.7 °F | 1.16 in. |
| March | 24.0 °F | 43.0 °F | 1.91 in. |
| April | 35.4 °F | 57.6 °F | 3.69 in. |
| May | 47.4 °F | 69.5 °F | 4.63 in. |
| June | 58.5 °F | 79.3 °F | 5.77 in. |
| July | 61.4 °F | 81.9 °F | 5.17 in. |
| August | 59.0 °F | 79.9 °F | 3.98 in. |
| September | 50.6 °F | 74.0 °F | 3.67 in. |
| October | 38.0 °F | 60.9 °F | 2.82 in. |
| November | 25.7 °F | 44.5 °F | 1.86 in. |
| December | 14.7 °F | 31.2 °F | 1.52 in. |
| Annual | 36.2 °F | 56.4 °F | 37.29 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4b : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |