Frost Dates for 50658 — Nashua, Iowa

Half of springs at Charles 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 14. Planting tender crops after May 6 leaves a 30% risk of a frost on them, after May 10 20%, and after May 14 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 58% 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 21 one year in ten, and holds off past October 19 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 6, 8 days before the 32°F one. The freeze-free season lasts 157 days in a typical year, shorter than at 77% of the 132 Iowa stations; it reaches 178 days one year in ten and falls short of 140 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 9 days longer, to about May 9, and return around September 27. Severe cold of 16°F or below comes every winter, usually between November 14 and March 21.

July is the warmest month at Charles City, IA, averaging 82°F by day and 62°F at night; January is the coldest at 25°F and 9°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 50% of years.

Warmth for growing adds up to 2,754 growing degree days a year (base 50°F), fewer than at 81% of the 132 Iowa stations. 35% of them (956) have built up by the end of June, and July adds the most, 683. Precipitation totals 37.6 inches a year, most in June (6.1") and least in January (1.0"); May to September bring 64% of it.

The nearest other station, New Hampton, IA, 13 miles northeast of Nashua and 155 feet higher, has a last frost 2 days later (May 2), a first frost 1 day earlier (October 5), a season 2 days shorter.

The first measurable snow (0.1 inch or more) in Nashua 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 Ionia 2 W, IA, 5.8 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 50658 is 10 miles from Charles City, IA, which stands at 993 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 50616 (Charles City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50658 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.