Frost Dates for 50140 — Lamoni, Iowa

Half of springs at Lamoni, IA 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 1. Planting tender crops after April 23 leaves a 30% risk of a frost on them, after April 27 20%, and after May 1 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 58% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 21 in half of years, as early as October 6 one year in ten, and holds off past November 2 one year in ten. A hard freeze of 28°F follows 9 days later, around October 30; in spring the one-in-ten date for 28°F is April 23, 8 days before the 32°F one. The freeze-free season lasts 184 days in a typical year, longer than at 89% of the 132 Iowa stations; it reaches 204 days one year in ten and falls short of 165 one year in ten. On average 132 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 29, and return around October 10. Severe cold of 16°F or below comes every winter, usually between November 25 and March 10.

July is the warmest month at Lamoni, IA, averaging 87°F by day and 66°F at night; January is the coldest at 33°F and 14°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 11% of years.

Warmth for growing adds up to 3,581 growing degree days a year (base 50°F), more than at 98% of the 132 Iowa stations. 35% of them (1,258) have built up by the end of June, and July adds the most, 828. Precipitation totals 41.2 inches a year, most in May (5.9") and least in January (1.1"); May to September bring 59% of it.

The nearest other station, Mt Ayr, IA, 16 miles west of Lamoni, has a last frost 8 days later (April 25), a first frost 9 days earlier (October 12), a season 15 days shorter.

The first measurable snow (0.1 inch or more) in Lamoni usually arrives around November 29, and the last of the season around March 18. Those are the middle dates across the winters of 1991–2020 at Lamoni, IA, 0.9 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 30 days after the last snow.

ZIP 50140 is under a mile from Lamoni, IA, which stands at 1,128 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50140 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.