Frost Dates for 06850 — Norwalk, Connecticut

Half of springs at Stamford 5 N, CT see their last 32°F night by April 17; only one in ten is past it by April 3, and one in ten still has one after May 2. Planting tender crops after April 23 leaves a 30% risk of a frost on them, after April 27 20%, and after May 2 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 50% of the 28 Connecticut stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 23 in half of years, as early as October 8 one year in ten, and holds off past November 6 one year in ten. A hard freeze of 28°F follows 10 days later, around November 2; in spring the one-in-ten date for 28°F is April 19, 13 days before the 32°F one. The freeze-free season lasts 188 days in a typical year, longer than at 64% of the 28 Connecticut stations; it reaches 208 days one year in ten and falls short of 168 one year in ten. On average 119 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 30, and return around October 12. Severe cold of 16°F or below comes every winter, usually between December 15 and March 4.

July is the warmest month at Stamford 5 N, CT, averaging 85°F by day and 64°F at night; January is the coldest at 38°F and 22°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 12% of years.

Warmth for growing adds up to 3,227 growing degree days a year (base 50°F), more than at 93% of the 28 Connecticut stations. 33% of them (1,055) have built up by the end of June, and July adds the most, 762. Precipitation totals 51.5 inches a year, most in September (5.2") and least in February (3.1"); May to September bring 42% of it.

The nearest other station, Westchester Co Airport, NY, 15 miles west of Norwalk and 189 feet higher, has a last frost 5 days earlier (April 12), a first frost 8 days later (October 31), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Norwalk usually arrives around December 8, and the last of the season around March 21. Those are the middle dates across the winters of 1991–2020 at Stamford 5 N, CT, 5.8 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 27 days after the last snow.

ZIP 06850 is 6 miles from Stamford 5 N, CT, which stands at 190 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 20 other ZIP codes share the station; its figures are presented in full for 06902 (Stamford). The 2023 USDA Plant Hardiness Zone Map lists ZIP 06850 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.