Frost Dates for 48238 — Detroit, Michigan

Half of springs at Dearborn #2, MI see their last 32°F night by April 27; only one in ten is past it by April 12, and one in ten still has one after May 11. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 6 20%, and after May 11 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 80% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 25 in half of years, as early as October 10 one year in ten, and holds off past November 7 one year in ten. A hard freeze of 28°F follows 12 days later, around November 6; in spring the one-in-ten date for 28°F is April 30, 11 days before the 32°F one. The freeze-free season lasts 181 days in a typical year, longer than at 96% of the 172 Michigan stations; it reaches 199 days one year in ten and falls short of 159 one year in ten. On average 125 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 9 days longer, to about May 6, and return around October 13. Severe cold of 16°F or below comes every winter, usually between December 11 and March 13.

July is the warmest month at Dearborn #2, MI, averaging 84°F by day and 63°F at night; January is the coldest at 33°F and 19°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 34% of years.

Warmth for growing adds up to 3,018 growing degree days a year (base 50°F), more than at 97% of the 172 Michigan stations. 32% of them (975) have built up by the end of June, and July adds the most, 736.

The nearest other station, Detroit City Airport, MI, 7 miles east of Detroit, has a last frost 6 days earlier (April 21), a first frost 6 days later (October 31), a season 9 days longer.

The first measurable snow (0.1 inch or more) in Detroit usually arrives around December 4, and the last of the season around March 26. Those are the middle dates across the winters of 1991–2020 at Dearborn, MI, 7.3 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 32 days after the last snow.

ZIP 48238 is 4 miles from Dearborn #2, MI, which stands at 605 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 17 other ZIP codes share the station; its figures are presented in full for 48228 (Detroit). The 2023 USDA Plant Hardiness Zone Map lists ZIP 48238 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.