Frost Dates for 56557 — Mahnomen, Minnesota

Half of springs at Mahnomen, MN see their last 32°F night by May 7; only one in ten is past it by April 27, and one in ten still has one after May 24. Planting tender crops after May 14 leaves a 30% risk of a frost on them, after May 18 20%, and after May 24 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 89% of the 142 Minnesota stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 28 in half of years, as early as September 15 one year in ten, and holds off past October 13 one year in ten. A hard freeze of 28°F follows 10 days later, around October 8; in spring the one-in-ten date for 28°F is May 12, 12 days before the 32°F one. The freeze-free season lasts 143 days in a typical year, shorter than at 71% of the 142 Minnesota stations; it reaches 161 days one year in ten and falls short of 122 one year in ten. On average 185 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 19, and return around September 19. Severe cold of 16°F or below comes every winter, usually between November 6 and April 4.

July is the warmest month at Mahnomen, MN, averaging 79°F by day and 58°F at night; January is the coldest at 15°F and -2°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 77% of years.

Warmth for growing adds up to 2,046 growing degree days a year (base 50°F), fewer than at 78% of the 142 Minnesota stations. 32% of them (652) have built up by the end of June, and July adds the most, 559.

The nearest other station, Fosston 1 E, MN, 18 miles northeast of Mahnomen, has a last frost 8 days later (May 15), a first frost 2 days earlier (September 26), a season 11 days shorter.

The first measurable snow (0.1 inch or more) in Mahnomen usually arrives around November 5, and the last of the season around April 11. Those are the middle dates across the winters of 1991–2020 at Tamarac Wildlife Re, MN, 27.8 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 26 days after the last snow.

ZIP 56557 is 4 miles from Mahnomen, MN, which stands at 1,212 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 56557 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°C) over 1991–2020; a zone describes winter lows, not frost dates.