Frost Dates for 53228 — Greenfield, Wisconsin

Half of springs at Hales Corners/Whitnall Park/Bo, WI see their last 32°F night by May 3; only one in ten is past it by April 18, and one in ten still has one after May 19. Planting tender crops after May 9 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 14 in half of years, as early as September 30 one year in ten, and holds off past October 26 one year in ten. A hard freeze of 28°F follows 10 days later, around October 24; 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 162 days in a typical year, longer than at 65% of the 182 Wisconsin stations; it reaches 181 days one year in ten and falls short of 142 one year in ten. On average 159 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 October 3. Severe cold of 16°F or below comes every winter, usually between November 24 and March 20.

July is the warmest month at Hales Corners/Whitnall Park/Bo, WI, averaging 83°F by day and 61°F at night; January is the coldest at 30°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 56% of years.

Warmth for growing adds up to 2,635 growing degree days a year (base 50°F), more than at 75% of the 182 Wisconsin stations. 31% of them (816) have built up by the end of June, and July adds the most, 671. Precipitation totals 38.6 inches a year, most in June (5.6") and least in January (1.8"); May to September bring 55% of it.

The nearest other station, West Allis, WI, 4 miles northeast of Greenfield, has a last frost 7 days earlier (April 26), a first frost 8 days later (October 22), a season 15 days longer.

The first measurable snow (0.1 inch or more) in Greenfield usually arrives around December 1, and the last of the season around March 25. Those are the middle dates across the winters of 1991–2020 at Hales Corners/Whitnall Park/Bo, WI, 2.1 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 39 days after the last snow.

ZIP 53228 is 2 miles from Hales Corners/Whitnall Park/Bo, WI, which stands at 774 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 53132 (Franklin). The 2023 USDA Plant Hardiness Zone Map lists ZIP 53228 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.