Frost Dates for 60585 — Plainfield, Illinois

Half of springs at Romeoville WFO, IL see their last 32°F night by April 20; only one in ten is past it by April 7, and one in ten still has one after May 6. Planting tender crops after April 27 leaves a 30% risk of a frost on them, after May 1 20%, and after May 6 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 22 in half of years, as early as October 7 one year in ten, and holds off past November 3 one year in ten. A hard freeze of 28°F follows 10 days later, around November 1; in spring the one-in-ten date for 28°F is April 23, 13 days before the 32°F one. The freeze-free season lasts 184 days in a typical year, shorter than at 51% of the 158 Illinois stations; it reaches 202 days one year in ten and falls short of 162 one year in ten. On average 123 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 1, and return around October 12. Severe cold of 16°F or below comes every winter, usually between November 29 and March 9.

July is the warmest month at Romeoville WFO, IL, averaging 85°F by day and 65°F at night; January is the coldest at 32°F and 16°F. A freezing night is all but certain in every month from November 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 21% of years.

Warmth for growing adds up to 3,305 growing degree days a year (base 50°F), fewer than at 64% of the 158 Illinois stations. 35% of them (1,144) have built up by the end of June, and July adds the most, 763. Precipitation totals 41.3 inches a year, most in May (4.8") and least in February (2.0"); May to September bring 53% of it.

The nearest other station, Aurora, IL, 10 miles northwest of Plainfield, has a last frost 1 day earlier (April 19), a first frost 1 day later (October 23), a season 1 day longer.

The first measurable snow (0.1 inch or more) in Plainfield usually arrives around December 2, and the last of the season around March 28. Those are the middle dates across the winters of 1991–2020 at Plainfield 3 NE, IL, 1.9 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 23 days after the last snow.

ZIP 60585 is 8 miles from Romeoville WFO, IL, which stands at 660 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 7 other ZIP codes share the station; its figures are presented in full for 60440 (Bolingbrook). The 2023 USDA Plant Hardiness Zone Map lists ZIP 60585 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.