Frost Dates for 60552 — Somonauk, Illinois

Half of springs at Chicago Aurora Municipal Airport, IL 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 11. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 11 10%. The 13 days between the even-odds date and the one-in-ten date is the narrowest of the 158 Illinois 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 27 one year in ten, and holds off past October 24 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 4, 7 days before the 32°F one. The freeze-free season lasts 166 days in a typical year, shorter than at 92% of the 158 Illinois stations; it reaches 185 days one year in ten and falls short of 145 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 8 days longer, to about May 6, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 22 and March 13.

July is the warmest month at Chicago Aurora Municipal Airport, IL, averaging 84°F by day and 62°F at night; January is the coldest at 31°F and 15°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 40% of years.

Warmth for growing adds up to 3,013 growing degree days a year (base 50°F), fewer than at 84% of the 158 Illinois stations. 35% of them (1,059) have built up by the end of June, and July adds the most, 716. Precipitation totals 33.9 inches a year, most in May (4.1") and least in January (1.3"); May to September bring 54% of it.

The nearest other station, Paw Paw 2S, IL, 15 miles west of Somonauk and 179 feet higher, has a last frost 1 day earlier (April 27), a first frost 2 days later (October 15), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Somonauk usually arrives around November 30, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Shabbona 3S, IL, 10.8 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 35 days after the last snow.

ZIP 60552 is 14 miles from Chicago Aurora Municipal Airport, IL, which stands at 710 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 60560 (Yorkville). The 2023 USDA Plant Hardiness Zone Map lists ZIP 60552 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.