Newcastle, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 43.5 °F (low) to 60.1 °F (high). Annual precipitation averages 48.5 Inches. Newcastle is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 11 - Mar. 20 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 35.3 °F | 45.9 °F | 6.7 in. |
| February | 35.2 °F | 48.7 °F | 4.62 in. |
| March | 37.3 °F | 52.6 °F | 5.12 in. |
| April | 40.6 °F | 58.4 °F | 4.18 in. |
| May | 46.2 °F | 65.9 °F | 2.65 in. |
| June | 50.4 °F | 69.9 °F | 2.33 in. |
| July | 54.2 °F | 76.5 °F | 0.89 in. |
| August | 54.5 °F | 77.1 °F | 1.26 in. |
| September | 50.6 °F | 71.0 °F | 1.96 in. |
| October | 44.2 °F | 60.0 °F | 4.89 in. |
| November | 38.6 °F | 50.5 °F | 7.18 in. |
| December | 34.8 °F | 44.8 °F | 6.68 in. |
| Annual | 43.5 °F | 60.1 °F | 48.46 in. |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 11 - Mar. 20 |
| Average Days With Frost | 30-40 Days |
| Plant Hardiness Zone | Zone 8b : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |