Frost Dates for 52353 — Washington, Iowa

Half of springs at Washington, IA see their last 32°F night by April 28; only one in ten is past it by April 13, and one in ten still has one after May 11. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 6 20%, and after May 11 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 25 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 11 days later, around October 22; in spring the one-in-ten date for 28°F is May 2, 9 days before the 32°F one. The freeze-free season lasts 165 days in a typical year, shorter than at 45% of the 132 Iowa stations; it reaches 186 days one year in ten and falls short of 147 one year in ten. On average 140 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 6, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 17 and March 16.

July is the warmest month at Washington, IA, averaging 85°F by day and 63°F at night; January is the coldest at 30°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 38% of years.

Warmth for growing adds up to 3,155 growing degree days a year (base 50°F), more than at 67% of the 132 Iowa stations. 35% of them (1,112) have built up by the end of June, and July adds the most, 746. Precipitation totals 38.0 inches a year, most in June (5.2") and least in January (1.3"); May to September bring 58% of it.

The nearest other station, Columbus Junction, IA, 18 miles east of Washington, has a last frost 2 days earlier (April 26), a first frost 1 day earlier (October 10), a season 2 days longer.

The first measurable snow (0.1 inch or more) in Washington usually arrives around December 3, and the last of the season around March 18. Those are the middle dates across the winters of 1991–2020 at Washington, IA, 1.3 miles away: half of years saw snow earlier, half later. Snow fell in 97% of those winters. The last 32°F night of spring typically comes 41 days after the last snow.

ZIP 52353 is 1 mile from Washington, IA, which stands at 687 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 52353 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.