Frost Dates for 61866 — Rantoul, Illinois

Half of springs at Rantoul, IL see their last 32°F night by April 21; 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 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 18 in half of years, as early as October 5 one year in ten, and holds off past October 31 one year in ten. A hard freeze of 28°F follows 11 days later, around October 29; in spring the one-in-ten date for 28°F is April 26, 10 days before the 32°F one. The freeze-free season lasts 179 days in a typical year, shorter than at 65% of the 158 Illinois stations; it reaches 197 days one year in ten and falls short of 159 one year in ten. On average 131 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 9 days longer, to about April 30, and return around October 8. Severe cold of 16°F or below comes every winter, usually between November 28 and March 11.

July is the warmest month at Rantoul, IL, averaging 88°F by day and 64°F at night; January is the coldest at 34°F and 16°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 20% of years.

Warmth for growing adds up to 3,623 growing degree days a year (base 50°F), more than at 60% of the 158 Illinois stations. 36% of them (1,311) have built up by the end of June, and July adds the most, 800. Precipitation totals 40.3 inches a year, most in June (4.6") and least in February (2.0"); May to September bring 51% of it.

The nearest other station, Paxton 2 WSW, IL, 10 miles north of Rantoul, has a last frost 2 days later (April 23), a first frost 6 days earlier (October 12), a season 9 days shorter.

The first measurable snow (0.1 inch or more) in Rantoul usually arrives around December 10, and the last of the season around February 27. Those are the middle dates across the winters of 1991–2020 at Rantoul, IL, 0.5 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 53 days after the last snow.

ZIP 61866 is under a mile from Rantoul, IL, which stands at 740 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61866 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.