Frost Dates for 53809 — Fennimore, Wisconsin

Half of springs at Boscobel Airport, 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 18. Planting tender crops after May 10 leaves a 30% risk of a frost on them, after May 13 20%, and after May 18 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 30% of the 182 Wisconsin stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 7 in half of years, as early as September 25 one year in ten, and holds off past October 20 one year in ten. A hard freeze of 28°F follows 10 days later, around October 17; in spring the one-in-ten date for 28°F is May 8, 10 days before the 32°F one. The freeze-free season lasts 155 days in a typical year, shorter than at 51% of the 182 Wisconsin stations; it reaches 176 days one year in ten and falls short of 138 one year in ten. On average 152 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 29. Severe cold of 16°F or below comes every winter, usually between November 18 and March 19.

July is the warmest month at Boscobel Airport, WI, averaging 84°F by day and 61°F at night; January is the coldest at 29°F and 10°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 58% of years.

Warmth for growing adds up to 2,891 growing degree days a year (base 50°F), more than at 95% of the 182 Wisconsin stations. 34% of them (990) have built up by the end of June, and July adds the most, 707. Precipitation totals 34.1 inches a year, most in June (5.2") and least in January (1.0"); May to September bring 61% of it.

The nearest other station, Lancaster 4 WSW, WI, 14 miles southwest of Fennimore and 368 feet higher, has a last frost 6 days earlier (April 27), a first frost 4 days later (October 11), a season 11 days longer.

The first measurable snow (0.1 inch or more) in Fennimore 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, 13.6 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 23 days after the last snow.

ZIP 53809 is 12 miles from Boscobel Airport, WI, which stands at 672 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 53805 (Boscobel). The 2023 USDA Plant Hardiness Zone Map lists ZIP 53809 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.