Frost Dates for 61938 — Mattoon, Illinois

Half of springs at Mattoon, IL see their last 32°F night by April 11; only one in ten is past it by March 31, and one in ten still has one after April 28. Planting tender crops after April 18 leaves a 30% risk of a frost on them, after April 22 20%, and after April 28 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 79% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 29 in half of years, as early as October 15 one year in ten, and holds off past November 9 one year in ten. A hard freeze of 28°F follows 9 days later, around November 7; in spring the one-in-ten date for 28°F is April 17, 11 days before the 32°F one. The freeze-free season lasts 199 days in a typical year, longer than at 85% of the 158 Illinois stations; it reaches 217 days one year in ten and falls short of 177 one year in ten. On average 108 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 23, and return around October 19. Severe cold of 16°F or below comes every winter, usually between December 6 and March 4.

July is the warmest month at Mattoon, IL, averaging 86°F by day and 67°F at night; January is the coldest at 35°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 86% of years.

Warmth for growing adds up to 3,793 growing degree days a year (base 50°F), more than at 72% of the 158 Illinois stations. 36% of them (1,368) have built up by the end of June, and July adds the most, 817. Precipitation totals 41.5 inches a year, most in April (4.8") and least in February (2.2"); May to September bring 46% of it.

The nearest other station, Neoga 4NW, IL, 11 miles southwest of Mattoon, has a last frost 5 days later (April 16), a first frost 9 days earlier (October 20), a season 14 days shorter.

The first measurable snow (0.1 inch or more) in Mattoon usually arrives around December 5, and the last of the season around March 7. Those are the middle dates across the winters of 1991–2020 at Mattoon, 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 35 days after the last snow.

ZIP 61938 is 1 mile from Mattoon, IL, which stands at 701 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61938 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.