Frost Dates for 50662 — Oelwein, Iowa

Half of springs at Oelwein 1E, IA see their last 32°F night by April 27; only one in ten is past it by April 12, and one in ten still has one after May 10. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 5 20%, and after May 10 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 13 in half of years, as early as September 30 one year in ten, and holds off past October 26 one year in ten. A hard freeze of 28°F follows 9 days later, around October 22; in spring the one-in-ten date for 28°F is May 2, 8 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 188 days one year in ten and falls short of 150 one year in ten. On average 156 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 5, and return around October 3. Severe cold of 16°F or below comes every winter, usually between November 17 and March 19.

July is the warmest month at Oelwein 1E, IA, averaging 83°F by day and 63°F at night; January is the coldest at 27°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 39% of years.

Warmth for growing adds up to 2,989 growing degree days a year (base 50°F), fewer than at 52% of the 132 Iowa stations. 35% of them (1,035) have built up by the end of June, and July adds the most, 716. Precipitation totals 35.4 inches a year, most in June (5.4") and least in January (1.1"); May to September bring 63% of it.

The nearest other station, Oelwein 2 S, IA, 3 miles south of Oelwein and 155 feet lower, has a last frost 3 days later (April 30), a first frost 4 days earlier (October 9), a season 6 days shorter.

The first measurable snow (0.1 inch or more) in Oelwein usually arrives around November 13, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Oelwein 2 S, IA, 2.5 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 41 days after the last snow.

ZIP 50662 is 2 miles from Oelwein 1E, IA, which stands at 1,165 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50662 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.