Frost Dates for 51534 — Glenwood, Iowa

Half of springs at Glenwood 3SW, IA see their last 32°F night by April 23; only one in ten is past it by April 9, and one in ten still has one after May 6. Planting tender crops after April 30 leaves a 30% risk of a frost on them, after May 2 20%, and after May 6 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 11 in half of years, as early as September 27 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 21; in spring the one-in-ten date for 28°F is April 27, 9 days before the 32°F one. The freeze-free season lasts 170 days in a typical year, longer than at 69% of the 132 Iowa stations; it reaches 190 days one year in ten and falls short of 150 one year in ten. On average 146 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 3, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 17 and March 14.

July is the warmest month at Glenwood 3SW, IA, averaging 87°F by day and 65°F at night; January is the coldest at 33°F and 12°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 25% of years.

Warmth for growing adds up to 3,476 growing degree days a year (base 50°F), more than at 93% of the 132 Iowa stations. 36% of them (1,237) have built up by the end of June, and July adds the most, 800. Precipitation totals 34.8 inches a year, most in June (6.0") and least in January (0.7"); May to September bring 65% of it.

The nearest other station, Springfield 7E, NE, 14 miles west of Glenwood, has a last frost 6 days earlier (April 17), a first frost 8 days later (October 19), a season 13 days longer.

The first measurable snow (0.1 inch or more) in Glenwood usually arrives around November 30, and the last of the season around March 14. Those are the middle dates across the winters of 1991–2020 at Glenwood 3SW, IA, 3 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 40 days after the last snow.

ZIP 51534 is 3 miles from Glenwood 3SW, IA, which stands at 980 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51534 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.