Jefferson, New York has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.1 °C (low) to 12.7 °C (high). Annual precipitation averages 1151.9 Millimeters. Jefferson is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.4 °C | -1.3 °C | 75.95 mm |
| February | -10.7 °C | -0.2 °C | 61.98 mm |
| March | -6.7 °C | 4.4 °C | 89.41 mm |
| April | -0.7 °C | 12.3 °C | 93.22 mm |
| May | 5.2 °C | 19.1 °C | 98.81 mm |
| June | 10.4 °C | 23.3 °C | 117.35 mm |
| July | 12.8 °C | 25.4 °C | 114.55 mm |
| August | 12.2 °C | 24.9 °C | 110.74 mm |
| September | 8.4 °C | 21.3 °C | 106.17 mm |
| October | 2.7 °C | 14.6 °C | 114.3 mm |
| November | -2.3 °C | 7 °C | 83.82 mm |
| December | -6.8 °C | 1.5 °C | 85.6 mm |
| Annual | 1.1 °C | 12.7 °C | 1151.9 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |