Frost Dates for 49707 — Alpena, Michigan

Half of springs at Alpena Wwtp, 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 21. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 17 20%, and after May 21 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 38% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 17 in half of years, as early as September 30 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 14 days later, around October 31; in spring the one-in-ten date for 28°F is May 13, 8 days before the 32°F one. The freeze-free season lasts 163 days in a typical year, longer than at 62% of the 172 Michigan stations; it reaches 184 days one year in ten and falls short of 142 one year in ten. On average 149 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 12 days longer, to about May 17, and return around October 4. Severe cold of 16°F or below comes every winter, usually between December 1 and March 25.

July is the warmest month at Alpena Wwtp, MI, averaging 77°F by day and 59°F at night; January is the coldest at 27°F and 13°F. A freezing night is all but certain in every month from November 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 64% of years.

Warmth for growing adds up to 2,001 growing degree days a year (base 50°F), fewer than at 78% of the 172 Michigan stations. 26% of them (517) have built up by the end of June, and July adds the most, 566. Precipitation totals 32.0 inches a year, most in August (3.5") and least in February (1.7"); May to September bring 49% of it.

The nearest other station, Alpena Co Regional Airport, MI, 5 miles west of Alpena, has a last frost 12 days later (May 17), a first frost 16 days earlier (October 1), a season 27 days shorter.

The first measurable snow (0.1 inch or more) in Alpena usually arrives around November 23, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Alpena Wwtp, MI, 2.5 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 34 days after the last snow.

ZIP 49707 is 3 miles from Alpena Wwtp, MI, which stands at 590 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 49707 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.