Frost Dates for 53901 — Portage, Wisconsin

Half of springs at Portage Wwtp, WI see their last 32°F night by April 28; only one in ten is past it by April 14, and one in ten still has one after May 12. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 7 20%, and after May 12 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 10 in half of years, as early as September 26 one year in ten, and holds off past October 23 one year in ten. A hard freeze of 28°F follows 12 days later, around October 22; in spring the one-in-ten date for 28°F is April 30, 12 days before the 32°F one. The freeze-free season lasts 164 days in a typical year, longer than at 71% of the 182 Wisconsin stations; it reaches 184 days one year in ten and falls short of 145 one year in ten. On average 148 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 10 days longer, to about May 8, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 23 and March 20.

July is the warmest month at Portage Wwtp, WI, averaging 82°F by day and 62°F at night; January is the coldest at 26°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 37% of years.

Warmth for growing adds up to 2,641 growing degree days a year (base 50°F), more than at 76% of the 182 Wisconsin stations. 34% of them (888) have built up by the end of June, and July adds the most, 670. Precipitation totals 38.4 inches a year, most in June (5.6") and least in January (1.4"); May to September bring 58% of it.

The nearest other station, Baraboo, WI, 14 miles southwest of Portage, has a last frost 7 days later (May 5), a first frost 5 days earlier (October 5), a season 12 days shorter.

The first measurable snow (0.1 inch or more) in Portage usually arrives around November 23, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Portage Wwtp, WI, 2.2 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 27 days after the last snow.

ZIP 53901 is 2 miles from Portage Wwtp, WI, which stands at 785 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 53901 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.