Frost Dates for 52310 — Monticello, Iowa

Half of springs at Anamosa 1 WNW, IA see their last 32°F night by May 1; only one in ten is past it by April 18, and one in ten still has one after May 18. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 12 20%, and after May 18 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 98% of the 132 Iowa stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 4 in half of years, as early as September 21 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 12 days later, around October 16; in spring the one-in-ten date for 28°F is May 6, 12 days before the 32°F one. The freeze-free season lasts 154 days in a typical year, shorter than at 84% of the 132 Iowa stations; it reaches 173 days one year in ten and falls short of 134 one year in ten. On average 152 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 May 13, and return around September 27. Severe cold of 16°F or below comes every winter, usually between November 14 and March 21.

July is the warmest month at Anamosa 1 WNW, IA, averaging 83°F by day and 62°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 53% of years.

Warmth for growing adds up to 2,766 growing degree days a year (base 50°F), fewer than at 80% of the 132 Iowa stations. 34% of them (953) have built up by the end of June, and July adds the most, 691. Precipitation totals 40.2 inches a year, most in June (5.8") and least in January (1.5"); May to September bring 60% of it.

The nearest other station, Cascade, IA, 11 miles northeast of Monticello, has a last frost 3 days earlier (April 28), a first frost 6 days later (October 10), a season 10 days longer.

The first measurable snow (0.1 inch or more) in Monticello usually arrives around December 7, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Anamosa 1 WNW, IA, 9.1 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 53 days after the last snow.

ZIP 52310 is 9 miles from Anamosa 1 WNW, IA, which stands at 805 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 52205 (Anamosa). The 2023 USDA Plant Hardiness Zone Map lists ZIP 52310 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.