Northumberland, New York has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37.6 °F (low) to 58.3 °F (high). Annual precipitation averages 45 Inches. Northumberland is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.5 °F | 31.5 °F | 3.32 in. |
| February | 14.5 °F | 34.6 °F | 2.5 in. |
| March | 23.5 °F | 43.6 °F | 3.29 in. |
| April | 35.4 °F | 57.9 °F | 3.72 in. |
| May | 46.7 °F | 70.2 °F | 3.63 in. |
| June | 55.8 °F | 78.3 °F | 4.56 in. |
| July | 60.1 °F | 83.0 °F | 4.53 in. |
| August | 58.8 °F | 80.9 °F | 4.25 in. |
| September | 51.2 °F | 73.8 °F | 3.84 in. |
| October | 40.3 °F | 60.8 °F | 4.31 in. |
| November | 30.4 °F | 48.1 °F | 3.35 in. |
| December | 21.5 °F | 36.6 °F | 3.74 in. |
| Annual | 37.6 °F | 58.3 °F | 45.04 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |