Frost Dates for 60448 — Mokena, Illinois

Half of springs at Park Forest, IL see their last 32°F night by April 23; only one in ten is past it by April 9, and one in ten still has one after May 11. Planting tender crops after April 30 leaves a 30% risk of a frost on them, after May 5 20%, and after May 11 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 20 in half of years, as early as October 6 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 10 days later, around October 30; in spring the one-in-ten date for 28°F is April 27, 14 days before the 32°F one. The freeze-free season lasts 179 days in a typical year, shorter than at 65% of the 158 Illinois stations; it reaches 198 days one year in ten and falls short of 159 one year in ten. On average 126 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 May 5, and return around October 10. Severe cold of 16°F or below comes every winter, usually between December 1 and March 12.

July is the warmest month at Park Forest, IL, averaging 84°F by day and 64°F at night; January is the coldest at 31°F and 15°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 29% of years.

Warmth for growing adds up to 3,114 growing degree days a year (base 50°F), fewer than at 77% of the 158 Illinois stations. 33% of them (1,040) have built up by the end of June, and July adds the most, 739. Precipitation totals 42.2 inches a year, most in June (4.9") and least in February (2.2"); May to September bring 51% of it.

The nearest other station, Romeoville WFO, IL, 11 miles northwest of Mokena, has a last frost 3 days earlier (April 20), a first frost 2 days later (October 22), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Mokena usually arrives around November 29, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Park Forest, IL, 11 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 60448 is 11 miles from Park Forest, IL, which stands at 710 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 38 other ZIP codes share the station; its figures are presented in full for 60411 (Chicago Heights). The 2023 USDA Plant Hardiness Zone Map lists ZIP 60448 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.