Gresham, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.9 °C (low) to 17.3 °C (high). Annual precipitation averages 1255.3 Millimeters. Gresham is located in USDA Plant Hardiness Zone 9a. 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 | 2.1 °C | 8.2 °C | 174.75 mm |
| February | 2.4 °C | 10.3 °C | 127.25 mm |
| March | 3.7 °C | 13.1 °C | 141.48 mm |
| April | 5.4 °C | 16.3 °C | 104.14 mm |
| May | 8.4 °C | 20.4 °C | 83.06 mm |
| June | 10.7 °C | 23.2 °C | 57.15 mm |
| July | 12.7 °C | 27.6 °C | 15.75 mm |
| August | 12.9 °C | 27.9 °C | 16.26 mm |
| September | 10.7 °C | 24.3 °C | 47.24 mm |
| October | 7.4 °C | 17.4 °C | 119.13 mm |
| November | 4.2 °C | 11.4 °C | 176.78 mm |
| December | 1.9 °C | 7.8 °C | 192.28 mm |
| Annual | 6.9 °C | 17.3 °C | 1255.27 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 30-40 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |