Frost Dates for 54840 — Grantsburg, Wisconsin

Half of springs at Grantsburg, WI see their last 32°F night by May 11; only one in ten is past it by April 27, and one in ten still has one after May 28. Planting tender crops after May 18 leaves a 30% risk of a frost on them, after May 23 20%, and after May 28 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 1 in half of years, as early as September 16 one year in ten, and holds off past October 14 one year in ten. A hard freeze of 28°F follows 10 days later, around October 11; in spring the one-in-ten date for 28°F is May 17, 11 days before the 32°F one. The freeze-free season lasts 141 days in a typical year, shorter than at 82% of the 182 Wisconsin stations; it reaches 160 days one year in ten and falls short of 117 one year in ten. On average 177 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 23, and return around September 22. Severe cold of 16°F or below comes every winter, usually between November 10 and April 2.

July is the warmest month at Grantsburg, WI, averaging 82°F by day and 58°F at night; January is the coldest at 22°F and 1°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 81% of years.

Warmth for growing adds up to 2,339 growing degree days a year (base 50°F), fewer than at 61% of the 182 Wisconsin stations. 33% of them (762) have built up by the end of June, and July adds the most, 626. Precipitation totals 34.1 inches a year, most in July (4.6") and least in January (0.9"); May to September bring 63% of it.

The nearest other station, Luck, WI, 15 miles southeast of Grantsburg and 230 feet higher, has a last frost 5 days earlier (May 6), a first frost 3 days later (October 4), a season 8 days longer.

The first measurable snow (0.1 inch or more) in Grantsburg usually arrives around November 6, and the last of the season around April 12. Those are the middle dates across the winters of 1991–2020 at Grantsburg, WI, 1.7 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 29 days after the last snow.

ZIP 54840 is 2 miles from Grantsburg, WI, which stands at 990 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 55069 (Rush City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 54840 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°C) over 1991–2020; a zone describes winter lows, not frost dates.