Frost Dates for 52591 — Sigourney, Iowa

Half of springs at Sigourney, IA see their last 32°F night by April 24; only one in ten is past it by April 9, and one in ten still has one after May 9. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 4 20%, and after May 9 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 82% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 15 in half of years, as early as September 30 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 9 days later, around October 24; in spring the one-in-ten date for 28°F is April 30, 9 days before the 32°F one. The freeze-free season lasts 172 days in a typical year, longer than at 73% of the 132 Iowa stations; it reaches 191 days one year in ten and falls short of 152 one year in ten. On average 142 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 10 days longer, to about May 4, and return around October 5. Severe cold of 16°F or below comes every winter, usually between November 21 and March 15.

July is the warmest month at Sigourney, IA, averaging 85°F by day and 63°F at night; January is the coldest at 30°F and 12°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 31% of years.

Warmth for growing adds up to 3,046 growing degree days a year (base 50°F), more than at 54% of the 132 Iowa stations. 34% of them (1,049) have built up by the end of June, and July adds the most, 733. Precipitation totals 37.5 inches a year, most in June (5.1") and least in January (1.2"); May to September bring 59% of it.

The nearest other station, Ottumwa Industrial Airport, IA, 20 miles southwest of Sigourney, has a last frost 1 day earlier (April 23), a first frost 1 day earlier (October 14).

The first measurable snow (0.1 inch or more) in Sigourney usually arrives around November 28, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Sigourney, IA, 1.7 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 38 days after the last snow.

ZIP 52591 is 2 miles from Sigourney, IA, which stands at 732 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 52591 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.