Putnam, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.4 °C (low) to 15.8 °C (high). Annual precipitation averages 1268.7 Millimeters. Putnam is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.6 °C | 2.5 °C | 98.81 mm |
| February | -7.9 °C | 3.8 °C | 86.11 mm |
| March | -3.7 °C | 8.1 °C | 113.03 mm |
| April | 1.8 °C | 15.2 °C | 113.28 mm |
| May | 7.3 °C | 21.1 °C | 87.88 mm |
| June | 12.4 °C | 25.5 °C | 108.97 mm |
| July | 15.9 °C | 28.4 °C | 100.08 mm |
| August | 14.6 °C | 27.4 °C | 108.2 mm |
| September | 10.8 °C | 23.6 °C | 108.46 mm |
| October | 4.7 °C | 17.2 °C | 122.68 mm |
| November | -0.9 °C | 11.1 °C | 102.36 mm |
| December | -5.4 °C | 5.4 °C | 118.87 mm |
| Annual | 3.4 °C | 15.8 °C | 1268.73 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |