Frost Dates for 48191 — Willis, Michigan

Half of springs at Milan 4 ESE, MI see their last 32°F night by May 3; only one in ten is past it by April 17, and one in ten still has one after May 25. Planting tender crops after May 12 leaves a 30% risk of a frost on them, after May 18 20%, and after May 25 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 98% of the 172 Michigan stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by October 10 in half of years, as early as September 25 one year in ten, and holds off past October 25 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 12, 13 days before the 32°F one. The freeze-free season lasts 158 days in a typical year, shorter than at 50% of the 172 Michigan stations; it reaches 179 days one year in ten and falls short of 133 one year in ten. On average 143 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 14 days longer, to about May 17, 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 Milan 4 ESE, MI, averaging 83°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 56% of years.

Warmth for growing adds up to 2,790 growing degree days a year (base 50°F), more than at 83% of the 172 Michigan stations. 33% of them (935) have built up by the end of June, and July adds the most, 679.

The nearest other station, Milan Wwtp, MI, 6 miles southwest of Willis, has a last frost 7 days earlier (April 26), a first frost 9 days later (October 19), a season 17 days longer.

The first measurable snow (0.1 inch or more) in Willis usually arrives around December 6, and the last of the season around March 18. Those are the middle dates across the winters of 1991–2020 at Milan 4 ESE, MI, 4.5 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 46 days after the last snow.

ZIP 48191 is 5 miles from Milan 4 ESE, MI, which stands at 670 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 48191 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.