Frost Dates for 48108 — Ann Arbor, Michigan

Half of springs at Ann Arbor Municipal Airport, MI see their last 32°F night by May 8; only one in ten is past it by April 23, and one in ten still has one after May 26. Planting tender crops after May 16 leaves a 30% risk of a frost on them, after May 22 20%, and after May 26 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 81% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 4 in half of years, as early as September 20 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 12 days later, around October 16; in spring the one-in-ten date for 28°F is May 15, 11 days before the 32°F one. The freeze-free season lasts 147 days in a typical year, shorter than at 69% of the 172 Michigan stations; it reaches 167 days one year in ten and falls short of 124 one year in ten. On average 150 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 16 days longer, to about May 24, and return around September 24. Severe cold of 16°F or below comes every winter, usually between November 22 and March 21.

July is the warmest month at Ann Arbor Municipal Airport, MI, averaging 84°F by day and 57°F at night; January is the coldest at 32°F and 15°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 73% of years.

Warmth for growing adds up to 2,545 growing degree days a year (base 50°F), more than at 57% of the 172 Michigan stations. 33% of them (844) have built up by the end of June, and July adds the most, 635. Precipitation totals 29.9 inches a year, most in June (3.6") and least in February (1.5"); May to September bring 53% of it.

The nearest other station, Ann Arbor SE, MI, 2 miles east of Ann Arbor, has a last frost 3 days earlier (May 5), a first frost 6 days later (October 10), a season 10 days longer.

The first measurable snow (0.1 inch or more) in Ann Arbor usually arrives around November 12, and the last of the season around April 16. Those are the middle dates across the winters of 1991–2020 at Ann Arbor SE, MI, 1.8 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 22 days after the last snow.

ZIP 48108 is 1 mile from Ann Arbor Municipal Airport, MI, which stands at 839 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 48103 (Ann Arbor). The 2023 USDA Plant Hardiness Zone Map lists ZIP 48108 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.