Frost Dates for 55811 — Duluth, Minnesota

Half of springs at Duluth, MN see their last 32°F night by May 13; only one in ten is past it by April 29, and one in ten still has one after May 29. Planting tender crops after May 19 leaves a 30% risk of a frost on them, after May 23 20%, and after May 29 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 77% of the 142 Minnesota 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 18 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 12 days later, around October 13; in spring the one-in-ten date for 28°F is May 16, 13 days before the 32°F one. The freeze-free season lasts 140 days in a typical year, shorter than at 78% of the 142 Minnesota stations; it reaches 161 days one year in ten and falls short of 120 one year in ten. On average 177 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 26, and return around September 23. Severe cold of 16°F or below comes every winter, usually between November 11 and April 4.

July is the warmest month at Duluth, MN, averaging 78°F by day and 56°F at night; January is the coldest at 20°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 85% of years.

Warmth for growing adds up to 1,789 growing degree days a year (base 50°F), fewer than at 89% of the 142 Minnesota stations. 28% of them (494) have built up by the end of June, and July adds the most, 525. Precipitation totals 31.3 inches a year, most in June (4.4") and least in January (1.0"); May to September bring 60% of it.

The nearest other station, Duluth NWS, MN, 2 miles northwest of Duluth, has a last frost 5 days later (May 18), the same first-frost date, a season 5 days shorter.

The first measurable snow (0.1 inch or more) in Duluth usually arrives around October 25, and the last of the season around April 27. Those are the middle dates across the winters of 1991–2020 at Duluth, MN, 1.7 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 16 days after the last snow.

ZIP 55811 is 2 miles from Duluth, MN, which stands at 1,428 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 55811 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.