Frost Dates for 05489 — Underhill, Vermont

Half of springs at Mt Mansfield, VT see their last 32°F night by May 23; only one in ten is past it by May 5, and one in ten still has one after June 8. Planting tender crops after May 29 leaves a 30% risk of a frost on them, after June 2 20%, and after June 8 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 78% of the 41 Vermont stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 30 in half of years, as early as September 16 one year in ten, and holds off past October 12 one year in ten. A hard freeze of 28°F follows 9 days later, around October 9; in spring the one-in-ten date for 28°F is May 29, 10 days before the 32°F one. The freeze-free season lasts 130 days in a typical year, shorter than at 88% of the 41 Vermont stations; it reaches 150 days one year in ten and falls short of 109 one year in ten. On average 198 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 10 days longer, to about June 2, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 6 and April 15.

July is the warmest month at Mt Mansfield, VT, averaging 69°F by day and 55°F at night; January is the coldest at 21°F and 6°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 23% of years.

Warmth for growing adds up to 1,296 growing degree days a year (base 50°F), the fewest of the 41 Vermont stations. 28% of them (368) have built up by the end of June, and July adds the most, 379. Precipitation totals 81.2 inches a year, most in June (7.9") and least in February (5.3"); May to September bring 45% of it.

The nearest other station, Essex Junction 1 N, VT, 10 miles west of Underhill and 3,610 feet lower, has a last frost 21 days earlier (May 2), a first frost 11 days later (October 11), a season 30 days longer.

The first measurable snow (0.1 inch or more) in Underhill usually arrives around October 15, and the last of the season around May 10. Those are the middle dates across the winters of 1991–2020 at Mt Mansfield, VT, 5.7 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 13 days after the last snow.

ZIP 05489 is 6 miles from Mt Mansfield, VT, which stands at 3,950 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 05489 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.