Frost Dates for 48818 — Crystal, Michigan

Half of springs at Alma, MI see their last 32°F night by May 1; only one in ten is past it by April 17, and one in ten still has one after May 19. Planting tender crops after May 8 leaves a 30% risk of a frost on them, after May 13 20%, and after May 19 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 13 in half of years, as early as September 29 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 15 days later, around October 28; in spring the one-in-ten date for 28°F is May 6, 13 days before the 32°F one. The freeze-free season lasts 164 days in a typical year, longer than at 65% of the 172 Michigan stations; it reaches 184 days one year in ten and falls short of 141 one year in ten. On average 156 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 13 days longer, to about May 14, and return around October 2. Severe cold of 16°F or below comes every winter, usually between December 1 and March 20.

July is the warmest month at Alma, MI, averaging 82°F by day and 59°F at night; January is the coldest at 29°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 53% of years.

Warmth for growing adds up to 2,519 growing degree days a year (base 50°F), more than at 53% of the 172 Michigan stations. 33% of them (824) have built up by the end of June, and July adds the most, 643. Precipitation totals 34.5 inches a year, most in May (3.7") and least in February (1.8"); May to September bring 49% of it.

The nearest other station, Greenville 2 NNE, MI, 17 miles west of Crystal and 153 feet higher, has a last frost 17 days later (May 18), a first frost 15 days earlier (September 28), a season 31 days shorter.

The first measurable snow (0.1 inch or more) in Crystal usually arrives around November 22, and the last of the season around April 7. Those are the middle dates across the winters of 1991–2020 at Alma, MI, 15.3 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 24 days after the last snow.

ZIP 48818 is 15 miles from Alma, MI, which stands at 729 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 7 other ZIP codes share the station; its figures are presented in full for 48801 (Alma). The 2023 USDA Plant Hardiness Zone Map lists ZIP 48818 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.