Frost Dates for 50563 — Manson, Iowa

Half of springs at Rockwell City, IA see their last 32°F night by April 26; only one in ten is past it by April 11, and one in ten still has one after May 6. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 3 20%, and after May 6 10%. The 10 days between the even-odds date and the one-in-ten date is the narrowest of the 132 Iowa stations behind this site's ZIP pages, so the end of frost is fairly predictable.

In fall the first 32°F night comes by October 10 in half of years, as early as September 27 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 11 days later, around October 21; in spring the one-in-ten date for 28°F is April 29, 7 days before the 32°F one. The freeze-free season lasts 167 days in a typical year, longer than at 60% of the 132 Iowa stations; it reaches 186 days one year in ten and falls short of 148 one year in ten. On average 154 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 4, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 16 and March 21.

July is the warmest month at Rockwell City, IA, averaging 83°F by day and 63°F at night; January is the coldest at 27°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 31% of years.

Warmth for growing adds up to 2,888 growing degree days a year (base 50°F), fewer than at 64% of the 132 Iowa stations. 35% of them (998) have built up by the end of June, and July adds the most, 710. Precipitation totals 33.8 inches a year, most in May (5.0") and least in January (0.8"); May to September bring 62% of it.

The nearest other station, Pocahontas, IA, 15 miles northwest of Manson, has the same 50% last-frost date, a first frost 3 days earlier (October 7), a season 3 days shorter.

The first measurable snow (0.1 inch or more) in Manson usually arrives around November 23, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Rockwell City, IA, 10 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 25 days after the last snow.

ZIP 50563 is 10 miles from Rockwell City, IA, which stands at 1,214 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 50579 (Rockwell City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50563 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.