Frost Dates for 53149 — Mukwonago, Wisconsin

Half of springs at Waukesha Wwtp, WI see their last 32°F night by May 1; only one in ten is past it by April 18, and one in ten still has one after May 18. Planting tender crops after May 7 leaves a 30% risk of a frost on them, after May 12 20%, and after May 18 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 90% 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 25 one year in ten. A hard freeze of 28°F follows 10 days later, around October 23; in spring the one-in-ten date for 28°F is May 5, 13 days before the 32°F one. The freeze-free season lasts 162 days in a typical year, longer than at 65% of the 182 Wisconsin stations; it reaches 183 days one year in ten and falls short of 144 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 12 days longer, to about May 13, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 22 and March 19.

July is the warmest month at Waukesha Wwtp, WI, averaging 81°F by day and 60°F at night; January is the coldest at 28°F and 12°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 53% of years.

Warmth for growing adds up to 2,535 growing degree days a year (base 50°F), more than at 63% of the 182 Wisconsin stations. 31% of them (798) have built up by the end of June, and July adds the most, 646. Precipitation totals 36.1 inches a year, most in June (4.9") and least in January (1.6"); May to September bring 57% of it.

The nearest other station, Rochester Wwtp, WI, 12 miles southeast of Mukwonago, has a last frost 4 days later (May 5), a first frost 3 days earlier (October 10), a season 6 days shorter.

The first measurable snow (0.1 inch or more) in Mukwonago usually arrives around November 24, and the last of the season around March 25. Those are the middle dates across the winters of 1991–2020 at Waukesha Wwtp, 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 37 days after the last snow.

ZIP 53149 is 10 miles from Waukesha Wwtp, WI, which stands at 789 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 53188 (Waukesha). The 2023 USDA Plant Hardiness Zone Map lists ZIP 53149 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.