Frost Dates for 62458 — Saint Elmo, Illinois

Half of springs at Brownstown 4 SW, IL see their last 32°F night by April 3; only one in ten is past it by March 19, and one in ten still has one after April 25. Planting tender crops after April 12 leaves a 30% risk of a frost on them, after April 18 20%, and after April 25 10%. The 22 days between the even-odds date and the one-in-ten date is the widest of the 158 Illinois stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by October 24 in half of years, as early as October 9 one year in ten, and holds off past November 8 one year in ten. A hard freeze of 28°F follows 11 days later, around November 4; in spring the one-in-ten date for 28°F is April 13, 12 days before the 32°F one. The freeze-free season lasts 202 days in a typical year, longer than at 90% of the 158 Illinois stations; it reaches 225 days one year in ten and falls short of 176 one year in ten. On average 105 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 15 days longer, to about April 18, and return around October 13. Severe cold of 16°F or below comes every winter, usually between December 7 and February 28.

July is the warmest month at Brownstown 4 SW, IL, averaging 87°F by day and 67°F at night; January is the coldest at 37°F and 21°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 59% of years.

Warmth for growing adds up to 3,921 growing degree days a year (base 50°F), more than at 80% of the 158 Illinois stations. 38% of them (1,478) have built up by the end of June, and July adds the most, 832. Precipitation totals 41.2 inches a year, most in May (5.3") and least in December (2.2"); May to September bring 48% of it.

The nearest other station, Vandalia, IL, 13 miles southwest of Saint Elmo, has a last frost 7 days later (April 10), the same first-frost date, a season 6 days shorter.

The first measurable snow (0.1 inch or more) in Saint Elmo usually arrives around December 10, and the last of the season around March 8. Those are the middle dates across the winters of 1991–2020 at Brownstown 4 SW, IL, 7.6 miles away: half of years saw snow earlier, half later. Snow fell in 93% of those winters. The last 32°F night of spring typically comes 26 days after the last snow.

ZIP 62458 is 8 miles from Brownstown 4 SW, IL, which stands at 530 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 62458 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.