Frost Dates for 53820 — Potosi, Wisconsin

Half of springs at Lancaster 4 WSW, WI see their last 32°F night by April 27; only one in ten is past it by April 11, and one in ten still has one after May 11. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 6 20%, and after May 11 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 58% of the 182 Wisconsin stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 11 in half of years, as early as September 27 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 11 days later, around October 22; in spring the one-in-ten date for 28°F is May 1, 10 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 187 days one year in ten and falls short of 146 one year in ten. On average 150 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 9 days longer, to about May 6, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 20 and March 19.

July is the warmest month at Lancaster 4 WSW, WI, averaging 81°F by day and 62°F at night; January is the coldest at 25°F and 9°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 38% of years.

Warmth for growing adds up to 2,650 growing degree days a year (base 50°F), more than at 77% of the 182 Wisconsin stations. 34% of them (898) have built up by the end of June, and July adds the most, 662. Precipitation totals 38.5 inches a year, most in June (5.9") and least in January (1.2"); May to September bring 60% of it.

The nearest other station, Dubuque L&D 11, IA, 11 miles south of Potosi and 420 feet lower, has a last frost 8 days earlier (April 19), a first frost 10 days later (October 21), a season 18 days longer.

The first measurable snow (0.1 inch or more) in Potosi usually arrives around November 14, and the last of the season around April 10. Those are the middle dates across the winters of 1991–2020 at Lancaster 4 WSW, WI, 10.4 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 17 days after the last snow.

ZIP 53820 is 10 miles from Lancaster 4 WSW, WI, which stands at 1,040 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 53813 (Lancaster). The 2023 USDA Plant Hardiness Zone Map lists ZIP 53820 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.