Frost Dates for 61920 — Charleston, Illinois

Half of springs at Charleston, IL see their last 32°F night by April 15; only one in ten is past it by April 1, and one in ten still has one after May 3. Planting tender crops after April 22 leaves a 30% risk of a frost on them, after April 26 20%, and after May 3 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 92% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 23 in half of years, as early as October 9 one year in ten, and holds off past November 4 one year in ten. A hard freeze of 28°F follows 10 days later, around November 2; in spring the one-in-ten date for 28°F is April 20, 13 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 209 days one year in ten and falls short of 163 one year in ten. On average 105 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 12 days longer, to about April 27, and return around October 12. Severe cold of 16°F or below comes every winter, usually between December 4 and March 5.

July is the warmest month at Charleston, IL, averaging 88°F by day and 66°F at night; January is the coldest at 38°F and 21°F. A freezing night is all but certain in every month from November 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 13% of years.

Warmth for growing adds up to 4,056 growing degree days a year (base 50°F), more than at 86% of the 158 Illinois stations. 38% of them (1,522) have built up by the end of June, and July adds the most, 842. Precipitation totals 43.6 inches a year, most in April (5.1") and least in January (2.5"); May to September bring 45% of it.

The nearest other station, Mattoon, IL, 10 miles west of Charleston, has a last frost 4 days earlier (April 11), a first frost 6 days later (October 29), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Charleston usually arrives around December 5, and the last of the season around March 8. Those are the middle dates across the winters of 1991–2020 at Charleston, IL, 1.5 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 38 days after the last snow.

ZIP 61920 is 2 miles from Charleston, IL, which stands at 700 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61920 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.