Frost Dates for 50659 — New Hampton, Iowa

Half of springs at New Hampton, IA see their last 32°F night by May 2; only one in ten is past it by April 17, 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 9 20%, and after May 14 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 5 in half of years, as early as September 23 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 10 days later, around October 15; in spring the one-in-ten date for 28°F is May 5, 9 days before the 32°F one. The freeze-free season lasts 155 days in a typical year, shorter than at 82% of the 132 Iowa stations; it reaches 173 days one year in ten and falls short of 137 one year in ten. On average 158 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 10, and return around September 28. Severe cold of 16°F or below comes every winter, usually between November 12 and March 24.

July is the warmest month at New Hampton, IA, averaging 81°F by day and 60°F at night; January is the coldest at 23°F and 6°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 55% of years.

Warmth for growing adds up to 2,499 growing degree days a year (base 50°F), fewer than at 98% of the 132 Iowa stations. 34% of them (847) have built up by the end of June, and July adds the most, 635. Precipitation totals 40.8 inches a year, most in June (6.6") and least in January (1.3"); May to September bring 61% of it.

The nearest other station, Charles City, IA, 18 miles west of New Hampton and 155 feet lower, has a last frost 2 days earlier (April 30), a first frost 1 day later (October 6), a season 2 days longer.

The first measurable snow (0.1 inch or more) in New Hampton usually arrives around November 20, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at New Hampton, IA, 1.9 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 39 days after the last snow.

ZIP 50659 is 2 miles from New Hampton, IA, which stands at 1,148 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50659 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.