Frost Dates for 50022 — Atlantic, Iowa

Half of springs at Atlantic 1 NE, IA see their last 32°F night by April 30; only one in ten is past it by April 17, and one in ten still has one after May 15. Planting tender crops after May 6 leaves a 30% risk of a frost on them, after May 9 20%, and after May 15 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 82% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 2 in half of years, as early as September 17 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 10 days later, around October 12; in spring the one-in-ten date for 28°F is May 5, 10 days before the 32°F one. The freeze-free season lasts 153 days in a typical year, shorter than at 89% of the 132 Iowa stations; it reaches 174 days one year in ten and falls short of 134 one year in ten. On average 152 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 25. Severe cold of 16°F or below comes every winter, usually between November 8 and March 26.

July is the warmest month at Atlantic 1 NE, IA, averaging 86°F by day and 64°F at night; January is the coldest at 31°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 49% of years.

Warmth for growing adds up to 3,215 growing degree days a year (base 50°F), more than at 75% of the 132 Iowa stations. 35% of them (1,136) have built up by the end of June, and July adds the most, 769. Precipitation totals 37.1 inches a year, most in June (5.7") and least in January (0.9"); May to September bring 63% of it.

The nearest other station, Audubon, IA, 21 miles north of Atlantic, has a last frost 2 days later (May 2), a first frost 1 day later (October 3), a season 1 day longer.

The first measurable snow (0.1 inch or more) in Atlantic usually arrives around November 18, and the last of the season around March 22. Those are the middle dates across the winters of 1991–2020 at Atlantic 1 NE, IA, 0.5 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 50022 is under a mile from Atlantic 1 NE, IA, which stands at 1,152 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50022 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.