Alta, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.1 °C (low) to 13.8 °C (high). Annual precipitation averages 817.9 Millimeters. Alta is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -12.7 °C | -3.4 °C | 18.8 mm |
| February | -10.4 °C | -1.1 °C | 23.11 mm |
| March | -3.7 °C | 6.7 °C | 44.45 mm |
| April | 2.4 °C | 14.5 °C | 89.92 mm |
| May | 9.6 °C | 21.2 °C | 112.78 mm |
| June | 15.7 °C | 26.7 °C | 131.83 mm |
| July | 17.4 °C | 27.9 °C | 86.87 mm |
| August | 15.8 °C | 26.6 °C | 111.76 mm |
| September | 11.2 °C | 23.8 °C | 75.95 mm |
| October | 4.2 °C | 16.4 °C | 58.67 mm |
| November | -3.1 °C | 7.2 °C | 37.08 mm |
| December | -9.2 °C | -0.6 °C | 26.67 mm |
| Annual | 3.1 °C | 13.8 °C | 817.89 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |