Frost Dates for 60189 — Wheaton, Illinois

Half of springs at Lisle-Morton Arboretum, 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 14. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 9 20%, and after May 14 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 22% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 16 in half of years, as early as October 1 one year in ten, and holds off past October 29 one year in ten. A hard freeze of 28°F follows 10 days later, around October 26; in spring the one-in-ten date for 28°F is May 4, 10 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, shorter than at 90% of the 158 Illinois stations; it reaches 188 days one year in ten and falls short of 148 one year in ten. On average 144 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 11 days longer, to about May 9, and return around October 6. Severe cold of 16°F or below comes every winter, usually between November 28 and March 15.

July is the warmest month at Lisle-Morton Arboretum, IL, averaging 84°F by day and 62°F at night; January is the coldest at 32°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 September 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 2,957 growing degree days a year (base 50°F), fewer than at 87% of the 158 Illinois stations. 33% of them (988) have built up by the end of June, and July adds the most, 716.

The nearest other station, West Chicago Dupage Airport, IL, 10 miles northwest of Wheaton, has a last frost 3 days earlier (April 25), a first frost 3 days later (October 19), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Wheaton usually arrives around November 24, and the last of the season around March 27. Those are the middle dates across the winters of 1991–2020 at Glen Ellyn 4S, IL, 1.8 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 32 days after the last snow.

ZIP 60189 is 2 miles from Lisle-Morton Arboretum, IL, which stands at 680 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 17 other ZIP codes share the station; its figures are presented in full for 60148 (Lombard). The 2023 USDA Plant Hardiness Zone Map lists ZIP 60189 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.