Frost Dates for 50583 — Sac City, Iowa

Half of springs at Sac City, IA see their last 32°F night by April 30; only one in ten is past it by April 15, and one in ten still has one after May 11. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 11 10%. The 11 days between the even-odds date and the one-in-ten date is narrower than at 88% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 6 in half of years, as early as September 23 one year in ten, and holds off past October 20 one year in ten. A hard freeze of 28°F follows 11 days later, around October 17; in spring the one-in-ten date for 28°F is May 2, 9 days before the 32°F one. The freeze-free season lasts 158 days in a typical year, shorter than at 76% of the 132 Iowa stations; it reaches 179 days one year in ten and falls short of 142 one year in ten. On average 159 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 8, and return around September 28. Severe cold of 16°F or below comes every winter, usually between November 12 and March 22.

July is the warmest month at Sac City, IA, averaging 83°F by day and 62°F at night; January is the coldest at 26°F and 8°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 47% of years.

Warmth for growing adds up to 2,776 growing degree days a year (base 50°F), fewer than at 79% of the 132 Iowa stations. 34% of them (951) have built up by the end of June, and July adds the most, 696. Precipitation totals 33.1 inches a year, most in June (5.1") and least in January (0.7"); May to September bring 63% of it.

The nearest other station, Storm Lake, IA, 18 miles northwest of Sac City and 232 feet higher, has a last frost 5 days earlier (April 25), a first frost 7 days later (October 13), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Sac City usually arrives around November 19, and the last of the season around April 2. Those are the middle dates across the winters of 1991–2020 at Sac City, 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 28 days after the last snow.

ZIP 50583 is 1 mile from Sac City, IA, which stands at 1,210 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50583 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.