Frost Dates for 60827 — Riverdale, Illinois

Half of springs at Chicago Midway Airport 3SW, IL see their last 32°F night by April 10; only one in ten is past it by March 30, and one in ten still has one after April 26. Planting tender crops after April 17 leaves a 30% risk of a frost on them, after April 20 20%, and after April 26 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 November 1 in half of years, as early as October 21 one year in ten, and holds off past November 16 one year in ten. A hard freeze of 28°F follows 10 days later, around November 11; in spring the one-in-ten date for 28°F is April 14, 12 days before the 32°F one. The freeze-free season lasts 203 days in a typical year, longer than at 92% of the 158 Illinois stations; it reaches 224 days one year in ten and falls short of 183 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 22, and return around October 22. Severe cold of 16°F or below comes every winter, usually between December 7 and March 3.

July is the warmest month at Chicago Midway Airport 3SW, IL, averaging 85°F by day and 68°F at night; January is the coldest at 33°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 3,592 growing degree days a year (base 50°F), more than at 59% of the 158 Illinois stations. 33% of them (1,201) have built up by the end of June, and July adds the most, 826. Precipitation totals 40.9 inches a year, most in May (4.8") and least in February (2.1"); May to September bring 51% of it.

The nearest other station, Park Forest, IL, 11 miles south of Riverdale, has a last frost 13 days later (April 23), a first frost 12 days earlier (October 20), a season 24 days shorter.

The first measurable snow (0.1 inch or more) in Riverdale usually arrives around November 21, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Chicago Midway Airport 3SW, IL, 9.6 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 9 days after the last snow.

ZIP 60827 is 10 miles from Chicago Midway Airport 3SW, IL, which stands at 620 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 19 other ZIP codes share the station; its figures are presented in full for 60628 (Chicago). The 2023 USDA Plant Hardiness Zone Map lists ZIP 60827 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.