Frost Dates for 61115 — Machesney Park, Illinois

Half of springs at Beloit, WI see their last 32°F night by May 1; only one in ten is past it by April 17, and one in ten still has one after May 16. Planting tender crops after May 7 leaves a 30% risk of a frost on them, after May 11 20%, and after May 16 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 12 in half of years, as early as September 28 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 11 days later, around October 23; in spring the one-in-ten date for 28°F is May 4, 12 days before the 32°F one. The freeze-free season lasts 162 days in a typical year, shorter than at 97% of the 158 Illinois stations; it reaches 182 days one year in ten and falls short of 144 one year in ten. On average 142 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 11, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 22 and March 19.

July is the warmest month at Beloit, WI, averaging 80°F by day and 60°F at night; January is the coldest at 25°F and 11°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 51% of years.

Warmth for growing adds up to 2,380 growing degree days a year (base 50°F), the fewest of the 158 Illinois stations. 32% of them (771) have built up by the end of June, and July adds the most, 611. Precipitation totals 37.3 inches a year, most in June (5.6") and least in February (1.5"); May to September bring 57% of it.

The nearest other station, Rockford Gtr Rockford Airport, IL, 11 miles south of Machesney Park, has a last frost 7 days earlier (April 24), a first frost 5 days later (October 17), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Machesney Park usually arrives around November 23, and the last of the season around April 2. Those are the middle dates across the winters of 1991–2020 at Roscoe 2 SE, IL, 4.8 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 61115 is 11 miles from Beloit, WI, which stands at 788 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 5 other ZIP codes share the station; its figures are presented in full for 53511 (Beloit). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61115 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.