Frost Dates for 05458 — Grand Isle, Vermont

Half of springs at S Hero, VT see their last 32°F night by April 28; only one in ten is past it by April 19, and one in ten still has one after May 10. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 5 20%, and after May 10 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 20 in half of years, as early as October 4 one year in ten, and holds off past November 2 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 29, 11 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, the longest of the 41 Vermont stations; it reaches 192 days one year in ten and falls short of 154 one year in ten. On average 141 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 11 days longer, to about May 9, and return around October 7. Severe cold of 16°F or below comes every winter, usually between November 29 and March 26.

July is the warmest month at S Hero, VT, averaging 82°F by day and 62°F at night; January is the coldest at 28°F and 11°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 38% of years.

Warmth for growing adds up to 2,576 growing degree days a year (base 50°F), more than at 93% of the 41 Vermont stations. 30% of them (778) have built up by the end of June, and July adds the most, 673. Precipitation totals 35.1 inches a year, most in June (4.1") and least in February (1.6"); May to September bring 52% of it.

The nearest other station, Plattsburgh International Airport, NY, 9 miles southwest of Grand Isle, has a last frost 8 days later (May 6), a first frost 15 days earlier (October 5), a season 22 days shorter.

The first measurable snow (0.1 inch or more) in Grand Isle usually arrives around November 18, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at S Hero, VT, 6 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 20 days after the last snow.

ZIP 05458 is 6 miles from S Hero, VT, which stands at 110 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 05468 (Milton). The 2023 USDA Plant Hardiness Zone Map lists ZIP 05458 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.