Frost Dates for 51249 — Sibley, Iowa

Half of springs at Sibley, IA see their last 32°F night by May 5; only one in ten is past it by April 22, and one in ten still has one after May 17. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 13 20%, and after May 17 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 3 in half of years, as early as September 21 one year in ten, and holds off past October 17 one year in ten. A hard freeze of 28°F follows 10 days later, around October 13; in spring the one-in-ten date for 28°F is May 8, 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 171 days one year in ten and falls short of 133 one year in ten. On average 173 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 7 days longer, to about May 12, and return around September 27. Severe cold of 16°F or below comes every winter, usually between November 9 and March 31.

July is the warmest month at Sibley, IA, averaging 82°F by day and 60°F at night; January is the coldest at 23°F and 5°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 69% of years.

Warmth for growing adds up to 2,569 growing degree days a year (base 50°F), fewer than at 95% of the 132 Iowa stations. 34% of them (861) have built up by the end of June, and July adds the most, 657. Precipitation totals 30.4 inches a year, most in June (4.9") and least in January (0.7"); May to September bring 63% of it.

The nearest other station, Sanborn, IA, 16 miles south of Sibley, has a last frost 4 days earlier (May 1), a first frost 4 days later (October 7), a season 8 days longer.

The first measurable snow (0.1 inch or more) in Sibley usually arrives around November 8, and the last of the season around April 11. Those are the middle dates across the winters of 1991–2020 at Sibley, IA, 0.5 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 24 days after the last snow.

ZIP 51249 is under a mile from Sibley, IA, which stands at 1,529 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51249 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.