Frost Dates for 62561 — Riverton, Illinois

Half of springs at Springfield Capital Airport, IL see their last 32°F night by April 14; only one in ten is past it by April 1, and one in ten still has one after April 29. Planting tender crops after April 20 leaves a 30% risk of a frost on them, after April 24 20%, and after April 29 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 20 in half of years, as early as October 5 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 10 days later, around October 30; in spring the one-in-ten date for 28°F is April 18, 11 days before the 32°F one. The freeze-free season lasts 187 days in a typical year, longer than at 54% of the 158 Illinois stations; it reaches 208 days one year in ten and falls short of 165 one year in ten. On average 111 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 April 25, and return around October 9. Severe cold of 16°F or below comes every winter, usually between December 1 and March 4.

July is the warmest month at Springfield Capital Airport, IL, averaging 87°F by day and 66°F at night; January is the coldest at 36°F and 20°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 89% of years.

Warmth for growing adds up to 3,874 growing degree days a year (base 50°F), more than at 78% of the 158 Illinois stations. 37% of them (1,444) have built up by the end of June, and July adds the most, 821. Precipitation totals 38.2 inches a year, most in June (4.6") and least in February (1.9"); May to September bring 51% of it.

The nearest other station, Springfield #2, IL, 9 miles southwest of Riverton, has a last frost 1 day later (April 15), a first frost 2 days later (October 22), a season 1 day longer.

The first measurable snow (0.1 inch or more) in Riverton usually arrives around December 7, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Sherman, IL, 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 28 days after the last snow.

ZIP 62561 is 8 miles from Springfield Capital Airport, IL, which stands at 594 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 62684 (Sherman). The 2023 USDA Plant Hardiness Zone Map lists ZIP 62561 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.