Frost Dates for 53586 — Shullsburg, Wisconsin

Half of springs at Darlington Wwtp, WI see their last 32°F night by May 3; only one in ten is past it by April 19, and one in ten still has one after May 19. Planting tender crops after May 10 leaves a 30% risk of a frost on them, after May 13 20%, and after May 19 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 70% of the 182 Wisconsin stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 4 in half of years, as early as September 20 one year in ten, and holds off past October 19 one year in ten. A hard freeze of 28°F follows 12 days later, around October 16; in spring the one-in-ten date for 28°F is May 9, 10 days before the 32°F one. The freeze-free season lasts 153 days in a typical year, shorter than at 57% of the 182 Wisconsin stations; it reaches 172 days one year in ten and falls short of 135 one year in ten. On average 158 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 11 days longer, to about May 14, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 17 and March 20.

July is the warmest month at Darlington Wwtp, WI, averaging 82°F by day and 60°F at night; January is the coldest at 27°F and 8°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 60% of years.

Warmth for growing adds up to 2,578 growing degree days a year (base 50°F), more than at 68% of the 182 Wisconsin stations. 34% of them (882) have built up by the end of June, and July adds the most, 649. Precipitation totals 37.7 inches a year, most in June (5.3") and least in January (1.3"); May to September bring 59% of it.

The nearest other station, Galena, IL, 14 miles southwest of Shullsburg, has a last frost 7 days earlier (April 26), a first frost 11 days later (October 15), a season 17 days longer.

The first measurable snow (0.1 inch or more) in Shullsburg usually arrives around November 23, and the last of the season around March 28. Those are the middle dates across the winters of 1991–2020 at Darlington Wwtp, WI, 9.9 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 36 days after the last snow.

ZIP 53586 is 10 miles from Darlington Wwtp, WI, which stands at 854 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 53530 (Darlington). The 2023 USDA Plant Hardiness Zone Map lists ZIP 53586 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.