Frost Dates for 51023 — Hawarden, Iowa

Half of springs at Hawarden, IA see their last 32°F night by May 1; 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 13 days between the even-odds date and the one-in-ten date is narrower than at 42% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 4 in half of years, as early as September 21 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 12 days later, around October 16; in spring the one-in-ten date for 28°F is May 4, 10 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 138 one year in ten. On average 166 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 7 days longer, to about May 8, and return around September 26. Severe cold of 16°F or below comes every winter, usually between November 10 and March 26.

July is the warmest month at Hawarden, IA, averaging 85°F by day and 62°F at night; January is the coldest at 27°F and 7°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 53% of years.

Warmth for growing adds up to 2,862 growing degree days a year (base 50°F), fewer than at 67% of the 132 Iowa stations. 34% of them (970) have built up by the end of June, and July adds the most, 728. Precipitation totals 30.0 inches a year, most in June (4.4") and least in January (0.7"); May to September bring 62% of it.

The nearest other station, Sioux Ctr 2 SE, IA, 16 miles east of Hawarden and 170 feet higher, has a last frost 1 day earlier (April 30), a first frost 1 day earlier (October 3), a season 1 day shorter.

The first measurable snow (0.1 inch or more) in Hawarden usually arrives around November 15, and the last of the season around March 29. Those are the middle dates across the winters of 1991–2020 at Hawarden, IA, 0.7 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 33 days after the last snow.

ZIP 51023 is under a mile from Hawarden, IA, which stands at 1,190 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51023 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.