Frost Dates for 61734 — Delavan, Illinois

Half of springs at Mason City 4SE, IL see their last 32°F night by April 17; only one in ten is past it by April 4, and one in ten still has one after May 4. Planting tender crops after April 23 leaves a 30% risk of a frost on them, after April 28 20%, and after May 4 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 79% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 18 in half of years, as early as October 4 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 11 days later, around October 29; in spring the one-in-ten date for 28°F is April 20, 14 days before the 32°F one. The freeze-free season lasts 182 days in a typical year, shorter than at 56% of the 158 Illinois stations; it reaches 202 days one year in ten and falls short of 161 one year in ten. On average 122 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 11 days longer, to about April 28, and return around October 7. Severe cold of 16°F or below comes every winter, usually between November 24 and March 10.

July is the warmest month at Mason City 4SE, IL, averaging 85°F by day and 65°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 15% of years.

Warmth for growing adds up to 3,481 growing degree days a year (base 50°F), fewer than at 53% of the 158 Illinois stations. 37% of them (1,275) have built up by the end of June, and July adds the most, 772. Precipitation totals 39.3 inches a year, most in July (5.1") and least in December (1.7"); May to September bring 53% of it.

The nearest other station, Lincoln, IL, 18 miles southeast of Delavan, has a last frost 3 days later (April 20), a first frost 2 days earlier (October 16), a season 3 days shorter.

The first measurable snow (0.1 inch or more) in Delavan usually arrives around December 3, and the last of the season around March 15. Those are the middle dates across the winters of 1991–2020 at Mackinaw 3WSW, IL, 12.5 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 33 days after the last snow.

ZIP 61734 is 15 miles from Mason City 4SE, IL, which stands at 600 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 62664 (Mason City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61734 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.