Frost Dates for 05495 — Williston, Vermont

Half of springs at Burlington International Airport, VT see their last 32°F night by April 29; only one in ten is past it by April 17, and one in ten still has one after May 11. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 6 20%, and after May 11 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 85% of the 41 Vermont stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 15 in half of years, as early as October 2 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 13 days later, around October 28; in spring the one-in-ten date for 28°F is April 30, 11 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, longer than at 98% of the 41 Vermont stations; it reaches 187 days one year in ten and falls short of 149 one year in ten. On average 145 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 9 days longer, to about May 8, and return around October 4. Severe cold of 16°F or below comes every winter, usually between November 30 and March 22.

July is the warmest month at Burlington International Airport, VT, averaging 82°F by day and 62°F at night; January is the coldest at 29°F and 13°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 41% of years.

Warmth for growing adds up to 2,724 growing degree days a year (base 50°F), more than at 98% of the 41 Vermont stations. 32% of them (868) have built up by the end of June, and July adds the most, 694. Precipitation totals 37.6 inches a year, most in June (4.3") and least in February (1.8"); May to September bring 52% of it.

The nearest other station, Essex Junction 1 N, VT, 4 miles north of Williston, has a last frost 3 days later (May 2), a first frost 4 days earlier (October 11), a season 9 days shorter.

The first measurable snow (0.1 inch or more) in Williston usually arrives around November 7, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Burlington International Airport, VT, 3 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 05495 is 3 miles from Burlington International Airport, VT, which stands at 330 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 05401 (Burlington). The 2023 USDA Plant Hardiness Zone Map lists ZIP 05495 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.