Frost Dates for 06357 — Niantic, Connecticut

Half of springs at Groton New London Airport, CT see their last 32°F night by April 16; only one in ten is past it by April 3, and one in ten still has one after April 30. Planting tender crops after April 21 leaves a 30% risk of a frost on them, after April 25 20%, and after April 30 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 28 Connecticut stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 28 in half of years, as early as October 13 one year in ten, and holds off past November 12 one year in ten. A hard freeze of 28°F follows 12 days later, around November 9; in spring the one-in-ten date for 28°F is April 17, 13 days before the 32°F one. The freeze-free season lasts 194 days in a typical year, longer than at 82% of the 28 Connecticut stations; it reaches 212 days one year in ten and falls short of 175 one year in ten. On average 107 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 13 days longer, to about April 29, and return around October 16. Severe cold of 16°F or below comes every winter, usually between December 20 and March 1.

July is the warmest month at Groton New London Airport, CT, averaging 80°F by day and 65°F at night; January is the coldest at 38°F and 23°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month.

Warmth for growing adds up to 2,786 growing degree days a year (base 50°F), fewer than at 54% of the 28 Connecticut stations. 27% of them (754) have built up by the end of June, and July adds the most, 691. Precipitation totals 39.2 inches a year, most in March (3.8") and least in February (2.2"); May to September bring 43% of it.

The nearest other station, Groton, CT, 9 miles east of Niantic, has a last frost 8 days earlier (April 8), a first frost 5 days later (November 2), a season 13 days longer.

The first measurable snow (0.1 inch or more) in Niantic usually arrives around December 13, and the last of the season around March 14. Those are the middle dates across the winters of 1991–2020 at Groton, CT, 9.2 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 33 days after the last snow.

ZIP 06357 is 8 miles from Groton New London Airport, CT, which stands at 10 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station; its figures are presented in full for 06320 (New London). The 2023 USDA Plant Hardiness Zone Map lists ZIP 06357 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.