Frost Dates for 50459 — Northwood, Iowa

Half of springs at Northwood, IA see their last 32°F night by May 4; only one in ten is past it by April 21, and one in ten still has one after May 16. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 12 20%, and after May 16 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 67% 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 20 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 9 days later, around October 13; in spring the one-in-ten date for 28°F is May 7, 9 days before the 32°F one. The freeze-free season lasts 152 days in a typical year, shorter than at 92% of the 132 Iowa stations; it reaches 169 days one year in ten and falls short of 135 one year in ten. On average 165 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 9 days longer, to about May 13, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 10 and March 29.

July is the warmest month at Northwood, IA, averaging 79°F by day and 59°F at night; January is the coldest at 21°F and 4°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 64% of years.

Warmth for growing adds up to 2,225 growing degree days a year (base 50°F), the fewest of the 132 Iowa stations. 34% of them (747) have built up by the end of June, and July adds the most, 589. Precipitation totals 35.4 inches a year, most in June (5.1") and least in February (1.0"); May to September bring 62% of it.

The nearest other station, Albert Lea 3SE, MN, 12 miles north of Northwood, has a last frost 7 days earlier (April 27), a first frost 5 days later (October 9), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Northwood usually arrives around November 16, and the last of the season around March 31. Those are the middle dates across the winters of 1991–2020 at Northwood, IA, 0.8 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 34 days after the last snow.

ZIP 50459 is under a mile from Northwood, IA, which stands at 1,190 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50459 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.