Frost Dates for 51201 — Sheldon, Iowa

Half of springs at Sheldon, IA see their last 32°F night by May 5; only one in ten is past it by April 24, and one in ten still has one after May 18. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 13 20%, and after May 18 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 42% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 28 in half of years, as early as September 14 one year in ten, and holds off past October 12 one year in ten. A hard freeze of 28°F follows 8 days later, around October 6; in spring the one-in-ten date for 28°F is May 9, 9 days before the 32°F one. The freeze-free season lasts 145 days in a typical year, the shortest of the 132 Iowa stations; it reaches 162 days one year in ten and falls short of 128 one year in ten. On average 171 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 8 days longer, to about May 13, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 4 and March 31.

July is the warmest month at Sheldon, IA, averaging 83°F by day and 60°F at night; January is the coldest at 25°F and 5°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 71% of years.

Warmth for growing adds up to 2,576 growing degree days a year (base 50°F), fewer than at 95% of the 132 Iowa stations. 34% of them (881) have built up by the end of June, and July adds the most, 668. Precipitation totals 31.1 inches a year, most in June (4.7") and least in January (0.9"); May to September bring 61% of it.

The nearest other station, Sanborn, IA, 10 miles east of Sheldon, has a last frost 4 days earlier (May 1), a first frost 9 days later (October 7), a season 15 days longer.

The first measurable snow (0.1 inch or more) in Sheldon usually arrives around November 4, and the last of the season around April 12. Those are the middle dates across the winters of 1991–2020 at Sheldon, IA, 0.4 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 23 days after the last snow.

ZIP 51201 is under a mile from Sheldon, IA, which stands at 1,420 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51201 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.