Frost Dates for 04578 — Wiscasset, Maine

Half of springs at Wiscasset Airport, ME see their last 32°F night by May 8; only one in ten is past it by April 26, and one in ten still has one after May 20. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 16 20%, and after May 20 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 67% of the 52 Maine stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 7 in half of years, as early as September 24 one year in ten, and holds off past October 21 one year in ten. A hard freeze of 28°F follows 14 days later, around October 21; in spring the one-in-ten date for 28°F is May 6, 14 days before the 32°F one. The freeze-free season lasts 151 days in a typical year, shorter than at 48% of the 52 Maine stations; it reaches 168 days one year in ten and falls short of 135 one year in ten. On average 160 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 12 days longer, to about May 20, and return around September 27. Severe cold of 16°F or below comes every winter, usually between November 26 and March 21.

July is the warmest month at Wiscasset Airport, ME, averaging 79°F by day and 58°F at night; January is the coldest at 32°F and 12°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 76% of years.

Warmth for growing adds up to 2,067 growing degree days a year (base 50°F), more than at 56% of the 52 Maine stations. 27% of them (554) have built up by the end of June, and July adds the most, 578. Precipitation totals 46.8 inches a year, most in October (5.1") and least in February (3.1"); May to September bring 40% of it.

The nearest other station, Newcastle, ME, 9 miles northeast of Wiscasset, has a last frost 11 days earlier (April 27), a first frost 11 days later (October 18), a season 21 days longer.

The first measurable snow (0.1 inch or more) in Wiscasset usually arrives around November 19, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Newcastle, ME, 8.7 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 25 days after the last snow.

ZIP 04578 is 2 miles from Wiscasset Airport, ME, which stands at 68 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 04578 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.