Frost Dates for 48118 — Chelsea, Michigan

Half of springs at Chelsea, MI see their last 32°F night by April 30; only one in ten is past it by April 18, and one in ten still has one after May 17. Planting tender crops after May 7 leaves a 30% risk of a frost on them, after May 11 20%, and after May 17 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 62% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 12 in half of years, as early as September 28 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 14 days later, around October 26; in spring the one-in-ten date for 28°F is May 6, 11 days before the 32°F one. The freeze-free season lasts 163 days in a typical year, longer than at 62% of the 172 Michigan stations; it reaches 184 days one year in ten and falls short of 140 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 11, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 29 and March 19.

July is the warmest month at Chelsea, MI, averaging 82°F by day and 61°F at night; January is the coldest at 31°F and 16°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 50% of years.

Warmth for growing adds up to 2,705 growing degree days a year (base 50°F), more than at 74% of the 172 Michigan stations. 34% of them (912) have built up by the end of June, and July adds the most, 665. Precipitation totals 34.6 inches a year, most in May (3.8") and least in February (2.0"); May to September bring 50% of it.

The nearest other station, Hell, MI, 8 miles north of Chelsea, has the same 50% last-frost date, a first frost 2 days later (October 14), a season 3 days longer.

The first measurable snow (0.1 inch or more) in Chelsea usually arrives around December 3, and the last of the season around March 31. Those are the middle dates across the winters of 1991–2020 at Chelsea, MI, 1.3 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 30 days after the last snow.

ZIP 48118 is 1 mile from Chelsea, MI, which stands at 900 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 48130 (Dexter). The 2023 USDA Plant Hardiness Zone Map lists ZIP 48118 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.