Frost Dates for 62522 — Decatur, Illinois

Half of springs at Decatur Wtp, IL see their last 32°F night by April 14; only one in ten is past it by April 1, and one in ten still has one after May 1. Planting tender crops after April 20 leaves a 30% risk of a frost on them, after April 24 20%, and after May 1 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 24 in half of years, as early as October 11 one year in ten, and holds off past November 5 one year in ten. A hard freeze of 28°F follows 10 days later, around November 3; in spring the one-in-ten date for 28°F is April 17, 14 days before the 32°F one. The freeze-free season lasts 192 days in a typical year, longer than at 75% of the 158 Illinois stations; it reaches 211 days one year in ten and falls short of 171 one year in ten. On average 110 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 26, and return around October 14. Severe cold of 16°F or below comes every winter, usually between December 2 and March 6.

July is the warmest month at Decatur Wtp, IL, averaging 85°F by day and 67°F at night; January is the coldest at 34°F and 20°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 90% of years and May still brings one in 11% of years.

Warmth for growing adds up to 3,664 growing degree days a year (base 50°F), more than at 63% of the 158 Illinois stations. 36% of them (1,331) have built up by the end of June, and July adds the most, 794. Precipitation totals 40.4 inches a year, most in May (5.0") and least in February (2.0"); May to September bring 50% of it.

The nearest other station, Decatur Airport, IL, 7 miles east of Decatur, has a last frost 2 days later (April 16), a first frost 2 days earlier (October 22), a season 5 days shorter.

The first measurable snow (0.1 inch or more) in Decatur 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 Decatur Wtp, IL, 3 miles away: half of years saw snow earlier, half later. Snow fell in 95% of those winters. The last 32°F night of spring typically comes 38 days after the last snow.

ZIP 62522 is 3 miles from Decatur Wtp, IL, which stands at 639 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 5 other ZIP codes share the station; its figures are presented in full for 62521 (Decatur). The 2023 USDA Plant Hardiness Zone Map lists ZIP 62522 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.