Frost Dates for 61254 — Geneseo, Illinois

Half of springs at Geneseo, IL see their last 32°F night by April 20; only one in ten is past it by April 6, and one in ten still has one after May 6. Planting tender crops after April 26 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 20 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 10 days later, around October 30; in spring the one-in-ten date for 28°F is April 25, 11 days before the 32°F one. The freeze-free season lasts 180 days in a typical year, shorter than at 60% of the 158 Illinois stations; it reaches 199 days one year in ten and falls short of 161 one year in ten. On average 126 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 9. Severe cold of 16°F or below comes every winter, usually between November 27 and March 11.

July is the warmest month at Geneseo, IL, averaging 86°F by day and 65°F at night; January is the coldest at 31°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 21% of years.

Warmth for growing adds up to 3,426 growing degree days a year (base 50°F), fewer than at 56% of the 158 Illinois stations. 36% of them (1,231) have built up by the end of June, and July adds the most, 787. Precipitation totals 39.1 inches a year, most in May (4.9") and least in January (1.6"); May to September bring 54% of it.

The nearest other station, Le Claire L&D 14, IA, 15 miles northwest of Geneseo, has a last frost 4 days earlier (April 16), a first frost 5 days later (October 25), a season 10 days longer.

The first measurable snow (0.1 inch or more) in Geneseo usually arrives around December 1, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Geneseo, IL, 1.1 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 34 days after the last snow.

ZIP 61254 is 1 mile from Geneseo, IL, which stands at 639 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61254 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.