Frost Dates for 50109 — Granger, Iowa

Half of springs at Des Moines Wsfo-Johnston, IA see their last 32°F night by April 19; only one in ten is past it by April 5, and one in ten still has one after May 3. Planting tender crops after April 25 leaves a 30% risk of a frost on them, after April 29 20%, and after May 3 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 18 in half of years, as early as October 1 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 9 days later, around October 27; in spring the one-in-ten date for 28°F is April 23, 10 days before the 32°F one. The freeze-free season lasts 179 days in a typical year, longer than at 86% of the 132 Iowa stations; it reaches 198 days one year in ten and falls short of 159 one year in ten. On average 135 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 11 days longer, to about April 30, and return around October 7. Severe cold of 16°F or below comes every winter, usually between November 21 and March 13.

July is the warmest month at Des Moines Wsfo-Johnston, IA, averaging 85°F by day and 66°F at night; January is the coldest at 30°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 September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 15% of years.

Warmth for growing adds up to 3,361 growing degree days a year (base 50°F), more than at 89% of the 132 Iowa stations. 35% of them (1,189) have built up by the end of June, and July adds the most, 780. Precipitation totals 36.4 inches a year, most in June (5.4") and least in January (1.0"); May to September bring 60% of it.

The nearest other station, Ankeny, IA, 9 miles east of Granger, has a last frost 4 days later (April 23), a first frost 3 days earlier (October 15), a season 6 days shorter.

The first measurable snow (0.1 inch or more) in Granger 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 Des Moines Wsfo-Johnston, IA, 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 21 days after the last snow.

ZIP 50109 is 5 miles from Des Moines Wsfo-Johnston, IA, which stands at 959 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 50322 (Urbandale). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50109 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.