Frost Dates for 51566 — Red Oak, Iowa

Half of springs at Red Oak, IA see their last 32°F night by April 24; only one in ten is past it by April 10, and one in ten still has one after May 8. Planting tender crops after April 30 leaves a 30% risk of a frost on them, after May 3 20%, and after May 8 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 13 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 23; in spring the one-in-ten date for 28°F is April 29, 9 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, longer than at 67% of the 132 Iowa stations; it reaches 189 days one year in ten and falls short of 149 one year in ten. On average 142 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 10 days longer, to about May 4, and return around October 3. Severe cold of 16°F or below comes every winter, usually between November 19 and March 15.

July is the warmest month at Red Oak, IA, averaging 86°F by day and 66°F at night; January is the coldest at 33°F and 13°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 30% of years.

Warmth for growing adds up to 3,441 growing degree days a year (base 50°F), more than at 92% of the 132 Iowa stations. 35% of them (1,220) have built up by the end of June, and July adds the most, 803. Precipitation totals 37.3 inches a year, most in May (6.0") and least in January (0.9"); May to September bring 61% of it.

The nearest other station, Shenandoah, IA, 18 miles southwest of Red Oak, has a last frost 4 days earlier (April 20), a first frost 4 days later (October 17), a season 10 days longer.

The first measurable snow (0.1 inch or more) in Red Oak usually arrives around November 25, and the last of the season around March 16. Those are the middle dates across the winters of 1991–2020 at Red Oak, IA, 0.9 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 51566 is under a mile from Red Oak, IA, which stands at 1,040 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51566 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.