Frost Dates for 48105 — Ann Arbor, Michigan

Half of springs at Ann Arbor U Of Mich, MI see their last 32°F night by May 3; only one in ten is past it by April 20, and one in ten still has one after May 20. Planting tender crops after May 10 leaves a 30% risk of a frost on them, after May 14 20%, and after May 20 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 13 in half of years, as early as September 29 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 13 days later, around October 26; in spring the one-in-ten date for 28°F is May 9, 11 days before the 32°F one. The freeze-free season lasts 160 days in a typical year, longer than at 51% of the 172 Michigan stations; it reaches 179 days one year in ten and falls short of 138 one year in ten. On average 130 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 13 days longer, to about May 16, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 28 and March 21.

July is the warmest month at Ann Arbor U Of Mich, MI, averaging 84°F by day and 60°F at night; January is the coldest at 32°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 59% of years.

Warmth for growing adds up to 2,801 growing degree days a year (base 50°F), more than at 84% of the 172 Michigan stations. 33% of them (936) have built up by the end of June, and July adds the most, 679. Precipitation totals 38.2 inches a year, most in June (3.9") and least in February (2.5"); May to September bring 47% of it.

The nearest other station, Ann Arbor SE, MI, 5 miles south of Ann Arbor, has a last frost 2 days later (May 5), a first frost 3 days earlier (October 10), a season 3 days shorter.

The first measurable snow (0.1 inch or more) in Ann Arbor usually arrives around November 10, and the last of the season around April 15. Those are the middle dates across the winters of 1991–2020 at Ann Arbor U Of Mich, MI, 2.2 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 18 days after the last snow.

ZIP 48105 is 2 miles from Ann Arbor U Of Mich, MI, which stands at 813 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 48105 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.