Frost Dates for 50669 — Reinbeck, Iowa

Half of springs at Grundy Ctr, IA see their last 32°F night by April 29; only one in ten is past it by April 15, and one in ten still has one after May 12. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 12 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 9 in half of years, as early as September 25 one year in ten, and holds off past October 20 one year in ten. A hard freeze of 28°F follows 9 days later, around October 18; in spring the one-in-ten date for 28°F is May 3, 9 days before the 32°F one. The freeze-free season lasts 160 days in a typical year, shorter than at 71% of the 132 Iowa stations; it reaches 180 days one year in ten and falls short of 142 one year in ten. On average 155 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 7, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 15 and March 21.

July is the warmest month at Grundy Ctr, IA, averaging 83°F by day and 62°F at night; January is the coldest at 26°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 43% of years.

Warmth for growing adds up to 2,866 growing degree days a year (base 50°F), fewer than at 66% of the 132 Iowa stations. 35% of them (1,000) have built up by the end of June, and July adds the most, 702. Precipitation totals 36.9 inches a year, most in June (5.7") and least in January (0.8"); May to September bring 63% of it.

The nearest other station, Waterloo Municipal Airport, IA, 19 miles northeast of Reinbeck, has a last frost 2 days earlier (April 27), a first frost 1 day later (October 10), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Reinbeck usually arrives around November 16, and the last of the season around March 31. Those are the middle dates across the winters of 1991–2020 at Grundy Ctr, IA, 8.2 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 29 days after the last snow.

ZIP 50669 is 8 miles from Grundy Ctr, IA, which stands at 985 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 50638 (Grundy Center). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50669 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.