Frost Dates for 48197 — Ypsilanti, Michigan

Half of springs at Ann Arbor SE, MI see their last 32°F night by May 5; only one in ten is past it by April 21, and one in ten still has one after May 20. Planting tender crops after May 11 leaves a 30% risk of a frost on them, after May 15 20%, and after May 20 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 55% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 10 in half of years, as early as September 28 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 13 days later, around October 23; in spring the one-in-ten date for 28°F is May 11, 9 days before the 32°F one. The freeze-free season lasts 157 days in a typical year, shorter than at 53% of the 172 Michigan stations; it reaches 176 days one year in ten and falls short of 138 one year in ten. On average 147 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 10 days longer, to about May 15, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 29 and March 20.

July is the warmest month at Ann Arbor SE, MI, averaging 84°F by day and 59°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 65% of years.

Warmth for growing adds up to 2,659 growing degree days a year (base 50°F), more than at 67% of the 172 Michigan stations. 33% of them (874) have built up by the end of June, and July adds the most, 666. Precipitation totals 37.8 inches a year, most in June (4.3") and least in February (2.4"); May to September bring 48% of it.

The nearest other station, Detroit Willow Run Airport, MI, 5 miles east of Ypsilanti, has a last frost 11 days earlier (April 24), a first frost 14 days later (October 24), a season 22 days longer.

The first measurable snow (0.1 inch or more) in Ypsilanti 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, 3.3 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 19 days after the last snow.

ZIP 48197 is 3 miles from Ann Arbor SE, MI, which stands at 832 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 48197 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.