Frost Dates for 52637 — Mediapolis, Iowa

Half of springs at Gladstone Dam 18, IL see their last 32°F night by April 8; only one in ten is past it by March 26, and one in ten still has one after April 23. Planting tender crops after April 14 leaves a 30% risk of a frost on them, after April 18 20%, and after April 23 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 82% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 29 in half of years, as early as October 17 one year in ten, and holds off past November 10 one year in ten. A hard freeze of 28°F follows 9 days later, around November 7; in spring the one-in-ten date for 28°F is April 13, 10 days before the 32°F one. The freeze-free season lasts 202 days in a typical year, the longest of the 132 Iowa stations; it reaches 220 days one year in ten and falls short of 182 one year in ten. On average 122 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 12 days longer, to about April 20, and return around October 19. Severe cold of 16°F or below comes every winter, usually between December 3 and March 5.

July is the warmest month at Gladstone Dam 18, IL, averaging 86°F by day and 67°F at night; January is the coldest at 32°F and 16°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 80% of years.

Warmth for growing adds up to 3,578 growing degree days a year (base 50°F), more than at 97% of the 132 Iowa stations. 35% of them (1,269) have built up by the end of June, and July adds the most, 812. Precipitation totals 37.3 inches a year, most in May (5.0") and least in January (1.4"); May to September bring 56% of it.

The nearest other station, New Boston Dam 17, IL, 13 miles north of Mediapolis, has a last frost 6 days later (April 14), a first frost 5 days earlier (October 24), a season 12 days shorter.

The first measurable snow (0.1 inch or more) in Mediapolis usually arrives around December 10, and the last of the season around February 28. Those are the middle dates across the winters of 1991–2020 at Gladstone Dam 18, IL, 10.6 miles away: half of years saw snow earlier, half later. Snow fell in 89% of those winters. The last 32°F night of spring typically comes 39 days after the last snow.

ZIP 52637 is 11 miles from Gladstone Dam 18, IL, which stands at 538 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 52637 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.