Frost Dates for 61342 — Mendota, Illinois

Half of springs at Paw Paw 2S, IL see their last 32°F night by April 27; only one in ten is past it by April 12, and one in ten still has one after May 12. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 6 20%, and after May 12 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 15 in half of years, as early as September 30 one year in ten, and holds off past October 26 one year in ten. A hard freeze of 28°F follows 10 days later, around October 25; in spring the one-in-ten date for 28°F is May 1, 11 days before the 32°F one. The freeze-free season lasts 171 days in a typical year, shorter than at 84% of the 158 Illinois stations; it reaches 189 days one year in ten and falls short of 151 one year in ten. On average 148 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 May 6, and return around October 5. Severe cold of 16°F or below comes every winter, usually between November 24 and March 15.

July is the warmest month at Paw Paw 2S, IL, averaging 82°F by day and 62°F at night; January is the coldest at 28°F and 12°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 38% of years.

Warmth for growing adds up to 2,824 growing degree days a year (base 50°F), fewer than at 92% of the 158 Illinois stations. 35% of them (978) have built up by the end of June, and July adds the most, 676. Precipitation totals 36.6 inches a year, most in May (4.8") and least in January (1.6"); May to September bring 56% of it.

The nearest other station, Peru, IL, 13 miles south of Mendota and 269 feet lower, has a last frost 3 days earlier (April 24), a first frost 3 days later (October 18), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Mendota usually arrives around November 30, and the last of the season around March 23. Those are the middle dates across the winters of 1991–2020 at Mendota 2 SE, IL, 1.4 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 35 days after the last snow.

ZIP 61342 is 11 miles from Paw Paw 2S, IL, which stands at 889 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61342 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.