Frost Dates for 60420 — Dwight, Illinois

Half of springs at Dwight, IL see their last 32°F night by April 27; only one in ten is past it by April 14, and one in ten still has one after May 14. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 8 20%, and after May 14 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 79% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 15 in half of years, as early as September 30 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 10 days later, around October 25; in spring the one-in-ten date for 28°F is May 2, 12 days before the 32°F one. The freeze-free season lasts 170 days in a typical year, shorter than at 87% of the 158 Illinois stations; it reaches 188 days one year in ten and falls short of 148 one year in ten. On average 140 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 7, and return around October 3. Severe cold of 16°F or below comes every winter, usually between November 25 and March 15.

July is the warmest month at Dwight, IL, averaging 84°F by day and 62°F at night; January is the coldest at 31°F and 14°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 3,037 growing degree days a year (base 50°F), fewer than at 84% of the 158 Illinois stations. 36% of them (1,079) have built up by the end of June, and July adds the most, 707. Precipitation totals 37.9 inches a year, most in May (4.9") and least in February (1.6"); May to September bring 54% of it.

The nearest other station, Pontiac, IL, 18 miles southwest of Dwight, has a last frost 11 days earlier (April 16), a first frost 9 days later (October 24), a season 21 days longer.

The first measurable snow (0.1 inch or more) in Dwight usually arrives around December 7, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Dwight, IL, 1.5 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 49 days after the last snow.

ZIP 60420 is 2 miles from Dwight, IL, which stands at 628 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 60420 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.