Frost Dates for 06811 — Danbury, Connecticut

Half of springs at Danbury, CT see their last 32°F night by April 20; only one in ten is past it by April 7, and one in ten still has one after May 6. Planting tender crops after April 26 leaves a 30% risk of a frost on them, after May 1 20%, and after May 6 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 20 in half of years, as early as October 5 one year in ten, and holds off past November 4 one year in ten. A hard freeze of 28°F follows 12 days later, around November 1; in spring the one-in-ten date for 28°F is April 21, 15 days before the 32°F one. The freeze-free season lasts 181 days in a typical year, longer than at 57% of the 28 Connecticut stations; it reaches 202 days one year in ten and falls short of 160 one year in ten. On average 126 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 3, and return around October 9. Severe cold of 16°F or below comes every winter, usually between December 10 and March 8.

July is the warmest month at Danbury, CT, averaging 85°F by day and 64°F at night; January is the coldest at 36°F and 21°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 21% of years.

Warmth for growing adds up to 3,102 growing degree days a year (base 50°F), more than at 86% of the 28 Connecticut stations. 33% of them (1,026) have built up by the end of June, and July adds the most, 759. Precipitation totals 53.0 inches a year, most in July (5.0") and least in February (3.3"); May to September bring 45% of it.

The nearest other station, Danbury Municipal Airport, CT, 4 miles south of Danbury, has a last frost 11 days later (May 1), a first frost 6 days earlier (October 14), a season 15 days shorter.

The first measurable snow (0.1 inch or more) in Danbury usually arrives around November 24, and the last of the season around April 4. Those are the middle dates across the winters of 1991–2020 at Danbury, CT, 3.1 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 16 days after the last snow.

ZIP 06811 is 3 miles from Danbury, CT, which stands at 405 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 8 other ZIP codes share the station; its figures are presented in full for 06810 (Danbury). The 2023 USDA Plant Hardiness Zone Map lists ZIP 06811 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.