Frost Dates for 61704 — Bloomington, Illinois

Half of springs at Normal 4NE, IL see their last 32°F night by April 25; only one in ten is past it by April 11, and one in ten still has one after May 11. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 5 20%, and after May 11 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 16 in half of years, as early as October 2 one year in ten, and holds off past October 29 one year in ten. A hard freeze of 28°F follows 11 days later, around October 27; in spring the one-in-ten date for 28°F is May 1, 10 days before the 32°F one. The freeze-free season lasts 172 days in a typical year, shorter than at 82% of the 158 Illinois stations; it reaches 192 days one year in ten and falls short of 152 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 May 4, and return around October 5. Severe cold of 16°F or below comes every winter, usually between November 26 and March 15.

July is the warmest month at Normal 4NE, IL, averaging 86°F by day and 63°F at night; January is the coldest at 33°F and 16°F. A freezing night is all but certain in every month from October 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 32% of years.

Warmth for growing adds up to 3,354 growing degree days a year (base 50°F), fewer than at 60% of the 158 Illinois stations. 36% of them (1,191) have built up by the end of June, and July adds the most, 759. Precipitation totals 39.3 inches a year, most in May (4.8") and least in February (2.0"); May to September bring 51% of it.

The nearest other station, Bloomington 5W, IL, 6 miles west of Bloomington, has a last frost 4 days earlier (April 21), a first frost 4 days later (October 20), a season 9 days longer.

The first measurable snow (0.1 inch or more) in Bloomington usually arrives around December 1, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Normal 4NE, IL, 6.3 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 39 days after the last snow.

ZIP 61704 is 6 miles from Normal 4NE, IL, which stands at 790 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 61761 (Normal). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61704 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.