Lake Oswego, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 7.3 °C (low) to 17.5 °C (high). Annual precipitation averages 1120.1 Millimeters. Lake Oswego is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Mar. 1 - Mar. 10 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2.4 °C | 8.6 °C | 164.08 mm |
| February | 2.7 °C | 10.7 °C | 115.06 mm |
| March | 3.9 °C | 13.4 °C | 127.76 mm |
| April | 5.8 °C | 16.4 °C | 98.81 mm |
| May | 8.8 °C | 20.4 °C | 68.33 mm |
| June | 11.2 °C | 23.2 °C | 42.67 mm |
| July | 13.4 °C | 27.5 °C | 10.41 mm |
| August | 13.5 °C | 27.8 °C | 12.95 mm |
| September | 11.2 °C | 24.6 °C | 42.16 mm |
| October | 7.7 °C | 17.9 °C | 98.81 mm |
| November | 4.6 °C | 11.7 °C | 167.64 mm |
| December | 2.2 °C | 8.1 °C | 171.45 mm |
| Annual | 7.3 °C | 17.5 °C | 1120.13 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 1 - Mar. 10 |
| Average Days With Frost | 20-30 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 |