St. Mary's, Newfoundland and Labrador climate data is summarized below. Average annual temperatures range from 37.1 °F (low) to 47.3 °F (high). Annual precipitation averages 48.3 Inches. St. Mary's is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -20.8 °F | -17.6 °F | 2260.6 in. |
| February | -21.3 °F | -18.2 °F | 2260.6 in. |
| March | -20.4 °F | -17.7 °F | 2108.2 in. |
| April | -18.5 °F | -15.4 °F | 2540 in. |
| May | -16.2 °F | -12.7 °F | 2336.8 in. |
| June | -14 °F | -10.3 °F | 2184.4 in. |
| July | -11.2 °F | -7.7 °F | 2438.4 in. |
| August | -10.4 °F | -7 °F | 2235.2 in. |
| September | -12.1 °F | -8.6 °F | 2794 in. |
| October | -14.2 °F | -11.4 °F | 3403.6 in. |
| November | -16.5 °F | -13.8 °F | 3505.2 in. |
| December | -18.9 °F | -16.1 °F | 3073.4 in. |
| Annual | 37.1 °F | 47.3 °F | 48.26 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |