Frost Dates for 61542 — Lewistown, Illinois

Half of springs at Havana, IL see their last 32°F night by April 17; only one in ten is past it by April 2, 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 16 days between the even-odds date and the one-in-ten date is narrower than at 22% 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 1 one year in ten, and holds off past October 31 one year in ten. A hard freeze of 28°F follows 10 days later, around October 29; in spring the one-in-ten date for 28°F is April 21, 12 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 202 days one year in ten and falls short of 162 one year in ten. On average 133 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 9 days longer, to about April 26, and return around October 8. Severe cold of 16°F or below comes every winter, usually between November 29 and March 8.

July is the warmest month at Havana, IL, averaging 88°F by day and 65°F at night; January is the coldest at 34°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 13% of years.

Warmth for growing adds up to 3,666 growing degree days a year (base 50°F), more than at 64% of the 158 Illinois stations. 36% of them (1,314) have built up by the end of June, and July adds the most, 824. Precipitation totals 41.1 inches a year, most in May (5.1") and least in January (2.2"); May to September bring 52% of it.

The nearest other station, Prairie City 2S, IL, 22 miles northwest of Lewistown and 187 feet higher, has the same 50% last-frost date, a first frost 3 days later (October 22).

The first measurable snow (0.1 inch or more) in Lewistown usually arrives around December 1, and the last of the season around March 15. Those are the middle dates across the winters of 1991–2020 at Havana, IL, 7.3 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 33 days after the last snow.

ZIP 61542 is 7 miles from Havana, IL, which stands at 463 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 61520 (Canton). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61542 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.