Frost Dates for 62326 — Colchester, Illinois

Half of springs at La Harpe, IL see their last 32°F night by April 21; only one in ten is past it by April 6, and one in ten still has one after May 5. Planting tender crops after April 27 leaves a 30% risk of a frost on them, after May 1 20%, and after May 5 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 82% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 19 in half of years, as early as October 4 one year in ten, and holds off past October 31 one year in ten. A hard freeze of 28°F follows 9 days later, around October 28; in spring the one-in-ten date for 28°F is April 25, 10 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 134 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 10 days longer, to about May 1, and return around October 8. Severe cold of 16°F or below comes every winter, usually between November 25 and March 12.

July is the warmest month at La Harpe, IL, averaging 85°F by day and 65°F at night; January is the coldest at 32°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 22% of years.

Warmth for growing adds up to 3,336 growing degree days a year (base 50°F), fewer than at 61% of the 158 Illinois stations. 36% of them (1,189) have built up by the end of June, and July adds the most, 764. Precipitation totals 38.9 inches a year, most in May (5.2") and least in January (1.6"); May to September bring 55% of it.

The nearest other station, Bentley, IL, 17 miles west of Colchester, has a last frost 8 days earlier (April 13), a first frost 3 days later (October 22), a season 11 days longer.

The first measurable snow (0.1 inch or more) in Colchester usually arrives around November 24, and the last of the season around March 20. Those are the middle dates across the winters of 1991–2020 at La Harpe, IL, 14.2 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 32 days after the last snow.

ZIP 62326 is 14 miles from La Harpe, IL, which stands at 690 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 62326 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.