Frost Dates for 53549 — Jefferson, Wisconsin

Half of springs at Jefferson Wwtp, WI see their last 32°F night by April 25; only one in ten is past it by April 12, and one in ten still has one after May 9. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 4 20%, and after May 9 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 18 in half of years, as early as October 2 one year in ten, and holds off past October 31 one year in ten. A hard freeze of 28°F follows 11 days later, around October 29; in spring the one-in-ten date for 28°F is April 29, 10 days before the 32°F one. The freeze-free season lasts 173 days in a typical year, longer than at 86% of the 182 Wisconsin stations; it reaches 193 days one year in ten and falls short of 153 one year in ten. On average 143 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 6, and return around October 5. Severe cold of 16°F or below comes every winter, usually between November 24 and March 18.

July is the warmest month at Jefferson Wwtp, WI, averaging 82°F by day and 62°F at night; January is the coldest at 27°F and 11°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 31% of years.

Warmth for growing adds up to 2,769 growing degree days a year (base 50°F), more than at 90% of the 182 Wisconsin stations. 33% of them (916) have built up by the end of June, and July adds the most, 694. Precipitation totals 38.7 inches a year, most in June (5.0") and least in January (1.6"); May to September bring 57% of it.

The nearest other station, Fort Atkinson, WI, 7 miles southwest of Jefferson, has a last frost 3 days later (April 28), a first frost 5 days earlier (October 13), a season 7 days shorter.

The first measurable snow (0.1 inch or more) in Jefferson usually arrives around November 23, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Jefferson Wwtp, WI, 0.6 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 32 days after the last snow.

ZIP 53549 is under a mile from Jefferson Wwtp, WI, which stands at 783 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 53549 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.