Frost Dates for 50161 — Maxwell, Iowa

Half of springs at Ames 5 SE, 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 8. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 4 20%, and after May 8 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 67% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 12 in half of years, as early as September 26 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 10 days later, around October 22; in spring the one-in-ten date for 28°F is April 30, 8 days before the 32°F one. The freeze-free season lasts 168 days in a typical year, longer than at 62% of the 132 Iowa stations; it reaches 187 days one year in ten and falls short of 147 one year in ten. On average 151 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 9 days longer, to about May 5, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 18 and March 16.

July is the warmest month at Ames 5 SE, IA, averaging 84°F by day and 63°F at night; January is the coldest at 28°F and 10°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 34% of years.

Warmth for growing adds up to 2,949 growing degree days a year (base 50°F), fewer than at 58% of the 132 Iowa stations. 35% of them (1,022) have built up by the end of June, and July adds the most, 719. Precipitation totals 38.1 inches a year, most in June (5.4") and least in January (1.0"); May to September bring 62% of it.

The nearest other station, Colo, IA, 11 miles north of Maxwell, has a last frost 2 days earlier (April 24), the same first-frost date, a season 2 days longer.

The first measurable snow (0.1 inch or more) in Maxwell usually arrives around November 24, and the last of the season around March 20. Those are the middle dates across the winters of 1991–2020 at Ames 5 SE, IA, 10.3 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 37 days after the last snow.

ZIP 50161 is 10 miles from Ames 5 SE, IA, which stands at 870 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 50124 (Huxley). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50161 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.