Lake Oswego, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 45.1 °F (low) to 63.5 °F (high). Annual precipitation averages 44.1 Inches. 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 | 36.4 °F | 47.4 °F | 6.46 in. |
| February | 36.8 °F | 51.2 °F | 4.53 in. |
| March | 39.1 °F | 56.1 °F | 5.03 in. |
| April | 42.5 °F | 61.5 °F | 3.89 in. |
| May | 47.9 °F | 68.7 °F | 2.69 in. |
| June | 52.2 °F | 73.8 °F | 1.68 in. |
| July | 56.2 °F | 81.5 °F | 0.41 in. |
| August | 56.3 °F | 82.1 °F | 0.51 in. |
| September | 52.1 °F | 76.2 °F | 1.66 in. |
| October | 45.8 °F | 64.2 °F | 3.89 in. |
| November | 40.2 °F | 53.1 °F | 6.6 in. |
| December | 36.0 °F | 46.6 °F | 6.75 in. |
| Annual | 45.1 °F | 63.5 °F | 44.1 in. |
| 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 : 20°F to 25°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |