Frost Dates for 06255 — North Grosvenordale, Connecticut

Half of springs at W Thompson Lake, CT see their last 32°F night by May 1; only one in ten is past it by April 20, and one in ten still has one after May 17. Planting tender crops after May 7 leaves a 30% risk of a frost on them, after May 11 20%, and after May 17 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 82% of the 28 Connecticut stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 9 in half of years, as early as September 30 one year in ten, and holds off past October 26 one year in ten. A hard freeze of 28°F follows 12 days later, around October 21; in spring the one-in-ten date for 28°F is May 2, 15 days before the 32°F one. The freeze-free season lasts 161 days in a typical year, shorter than at 86% of the 28 Connecticut stations; it reaches 181 days one year in ten and falls short of 140 one year in ten. On average 156 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 May 14, and return around October 1. Severe cold of 16°F or below comes every winter, usually between December 1 and March 16.

July is the warmest month at W Thompson Lake, CT, averaging 82°F by day and 60°F at night; January is the coldest at 35°F and 15°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 52% of years.

Warmth for growing adds up to 2,489 growing degree days a year (base 50°F), fewer than at 82% of the 28 Connecticut stations. 30% of them (756) have built up by the end of June, and July adds the most, 654. Precipitation totals 50.1 inches a year, most in October (4.8") and least in May (3.4"); May to September bring 40% of it.

The nearest other station, Buffumville Lake, MA, 9 miles north of North Grosvenordale and 160 feet higher, has the same 50% last-frost date, a first frost 1 day later (October 10), a season 1 day longer.

The first measurable snow (0.1 inch or more) in North Grosvenordale usually arrives around December 9, and the last of the season around March 20. Those are the middle dates across the winters of 1991–2020 at W Thompson Lake, CT, 3.2 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 42 days after the last snow.

ZIP 06255 is 3 miles from W Thompson Lake, CT, which stands at 360 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 06260 (Putnam). The 2023 USDA Plant Hardiness Zone Map lists ZIP 06255 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.