Frost Dates for 53538 — Fort Atkinson, Wisconsin

Half of springs at Fort Atkinson, WI see their last 32°F night by April 28; only one in ten is past it by April 14, and one in ten still has one after May 17. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 10 20%, and after May 17 10%. The 19 days between the even-odds date and the one-in-ten date is the widest of the 182 Wisconsin 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 26 one year in ten. A hard freeze of 28°F follows 11 days later, around October 24; in spring the one-in-ten date for 28°F is May 3, 14 days before the 32°F one. The freeze-free season lasts 166 days in a typical year, longer than at 76% of the 182 Wisconsin stations; it reaches 185 days one year in ten and falls short of 145 one year in ten. On average 146 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 10, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 24 and March 17.

July is the warmest month at Fort Atkinson, WI, averaging 83°F by day and 62°F at night; January is the coldest at 28°F and 11°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 42% of years.

Warmth for growing adds up to 2,751 growing degree days a year (base 50°F), more than at 88% of the 182 Wisconsin stations. 33% of them (920) have built up by the end of June, and July adds the most, 685. Precipitation totals 35.5 inches a year, most in June (5.0") and least in February (1.4"); May to September bring 57% of it.

The nearest other station, Jefferson Wwtp, WI, 5 miles northeast of Fort Atkinson, has a last frost 3 days earlier (April 25), a first frost 5 days later (October 18), a season 7 days longer.

The first measurable snow (0.1 inch or more) in Fort Atkinson usually arrives around November 24, and the last of the season around March 27. Those are the middle dates across the winters of 1991–2020 at Fort Atkinson, WI, 1.5 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 32 days after the last snow.

ZIP 53538 is 2 miles from Fort Atkinson, WI, which stands at 800 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 53538 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.