Frost Dates for 61455 — Macomb, Illinois

Half of springs at Prairie City 2S, IL see their last 32°F night by April 17; only one in ten is past it by April 4, and one in ten still has one after May 2. Planting tender crops after April 23 leaves a 30% risk of a frost on them, after April 28 20%, and after May 2 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 22 in half of years, as early as October 7 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 8 days later, around October 30; in spring the one-in-ten date for 28°F is April 21, 11 days before the 32°F one. The freeze-free season lasts 185 days in a typical year, longer than at 50% of the 158 Illinois stations; it reaches 203 days one year in ten and falls short of 166 one year in ten. On average 127 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 11 days longer, to about April 28, and return around October 12. Severe cold of 16°F or below comes every winter, usually between November 27 and March 12.

July is the warmest month at Prairie City 2S, IL, averaging 86°F by day and 64°F at night; January is the coldest at 33°F and 16°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 12% of years.

Warmth for growing adds up to 3,482 growing degree days a year (base 50°F), fewer than at 52% of the 158 Illinois stations. 36% of them (1,259) have built up by the end of June, and July adds the most, 776. Precipitation totals 38.5 inches a year, most in May (5.1") and least in December (1.8"); May to September bring 55% of it.

The nearest other station, La Harpe, IL, 18 miles northwest of Macomb, has a last frost 4 days later (April 21), a first frost 3 days earlier (October 19), a season 5 days shorter.

The first measurable snow (0.1 inch or more) in Macomb usually arrives around December 1, and the last of the season around March 18. Those are the middle dates across the winters of 1991–2020 at Prairie City 2S, 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 30 days after the last snow.

ZIP 61455 is 14 miles from Prairie City 2S, IL, which stands at 650 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61455 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.