Frost Dates for 52653 — Wapello, Iowa

Half of springs at New Boston Dam 17, IL see their last 32°F night by April 14; only one in ten is past it by April 1, and one in ten still has one after May 2. Planting tender crops after April 21 leaves a 30% risk of a frost on them, after April 27 20%, and after May 2 10%. The 18 days between the even-odds date and the one-in-ten date is the widest of the 132 Iowa 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 9 one year in ten, and holds off past November 4 one year in ten. A hard freeze of 28°F follows 8 days later, around November 1; in spring the one-in-ten date for 28°F is April 21, 11 days before the 32°F one. The freeze-free season lasts 190 days in a typical year, longer than at 96% of the 132 Iowa stations; it reaches 209 days one year in ten and falls short of 169 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 13 days longer, to about April 27, and return around October 14. Severe cold of 16°F or below comes every winter, usually between December 1 and March 8.

July is the warmest month at New Boston Dam 17, IL, averaging 86°F by day and 65°F at night; January is the coldest at 32°F and 15°F. A freezing night is all but certain in every month from November 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 12% of years.

Warmth for growing adds up to 3,439 growing degree days a year (base 50°F), more than at 90% of the 132 Iowa stations. 36% of them (1,223) have built up by the end of June, and July adds the most, 795. Precipitation totals 36.3 inches a year, most in May (5.1") and least in January (1.3"); May to September bring 56% of it.

The nearest other station, Columbus Junction, IA, 12 miles northwest of Wapello, has a last frost 12 days later (April 26), a first frost 14 days earlier (October 10), a season 23 days shorter.

The first measurable snow (0.1 inch or more) in Wapello usually arrives around December 1, and the last of the season around March 25. Those are the middle dates across the winters of 1991–2020 at Wapello, IA, 1.2 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 20 days after the last snow.

ZIP 52653 is 6 miles from New Boston Dam 17, IL, which stands at 548 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 52653 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.