Frost Dates for 62471 — Vandalia, Illinois

Half of springs at Vandalia, IL see their last 32°F night by April 10; only one in ten is past it by March 28, and one in ten still has one after April 24. Planting tender crops after April 17 leaves a 30% risk of a frost on them, after April 20 20%, and after April 24 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 82% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 24 in half of years, as early as October 11 one year in ten, and holds off past November 5 one year in ten. A hard freeze of 28°F follows 10 days later, around November 3; in spring the one-in-ten date for 28°F is April 16, 8 days before the 32°F one. The freeze-free season lasts 196 days in a typical year, longer than at 81% of the 158 Illinois stations; it reaches 215 days one year in ten and falls short of 174 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 14. Severe cold of 16°F or below comes every winter, usually between December 7 and February 28.

July is the warmest month at Vandalia, 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 82% of years.

Warmth for growing adds up to 3,847 growing degree days a year (base 50°F), more than at 75% of the 158 Illinois stations. 37% of them (1,417) have built up by the end of June, and July adds the most, 828. Precipitation totals 43.9 inches a year, most in May (5.3") and least in February (2.5"); May to September bring 46% of it.

The nearest other station, Brownstown 4 SW, IL, 8 miles east of Vandalia, has a last frost 7 days earlier (April 3), the same first-frost date, a season 6 days longer.

The first measurable snow (0.1 inch or more) in Vandalia usually arrives around December 7, and the last of the season around March 1. Those are the middle dates across the winters of 1991–2020 at Vandalia, IL, 0.8 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 40 days after the last snow.

ZIP 62471 is under a mile from Vandalia, IL, which stands at 490 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 62471 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.