Frost Dates for 49905 — Atlantic Mine, Michigan

Half of springs at Hancock Houghton Co Airport, MI see their last 32°F night by May 17; only one in ten is past it by May 1, and one in ten still has one after June 3. Planting tender crops after May 24 leaves a 30% risk of a frost on them, after May 30 20%, and after June 3 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 1 in half of years, as early as September 16 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 13 days later, around October 14; in spring the one-in-ten date for 28°F is May 20, 14 days before the 32°F one. The freeze-free season lasts 138 days in a typical year, shorter than at 75% of the 172 Michigan stations; it reaches 159 days one year in ten and falls short of 116 one year in ten. On average 175 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 15 days longer, to about June 1, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 20 and April 5.

July is the warmest month at Hancock Houghton Co Airport, MI, averaging 75°F by day and 55°F at night; January is the coldest at 22°F and 10°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 89% of years and June still brings one in 16% of years.

Warmth for growing adds up to 1,605 growing degree days a year (base 50°F), fewer than at 96% of the 172 Michigan stations. 27% of them (428) have built up by the end of June, and July adds the most, 467.

The nearest other station, Jacobsville, MI, 15 miles southeast of Atlantic Mine and 413 feet lower, has a last frost 15 days later (June 1), a first frost 8 days earlier (September 23), a season 23 days shorter.

The first measurable snow (0.1 inch or more) in Atlantic Mine usually arrives around October 30, and the last of the season around April 18. Those are the middle dates across the winters of 1991–2020 at Ontonagon 6 SE, MI, 29.5 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 29 days after the last snow.

ZIP 49905 is 12 miles from Hancock Houghton Co Airport, MI, which stands at 1,063 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station; its figures are presented in full for 49931 (Houghton). The 2023 USDA Plant Hardiness Zone Map lists ZIP 49905 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.