Frost Dates for 57717 — Belle Fourche, South Dakota

Half of springs at Belle Fourche, SD see their last 32°F night by May 10; only one in ten is past it by April 27, and one in ten still has one after May 25. Planting tender crops after May 16 leaves a 30% risk of a frost on them, after May 20 20%, and after May 25 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 84% of the 49 South Dakota stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 30 in half of years, as early as September 16 one year in ten, and holds off past October 13 one year in ten. A hard freeze of 28°F follows 10 days later, around October 10; in spring the one-in-ten date for 28°F is May 15, 10 days before the 32°F one. The freeze-free season lasts 143 days in a typical year, shorter than at 76% of the 49 South Dakota stations; it reaches 161 days one year in ten and falls short of 120 one year in ten. On average 167 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 11 days longer, to about May 21, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 6 and April 1.

July is the warmest month at Belle Fourche, SD, averaging 87°F by day and 60°F at night; January is the coldest at 37°F and 13°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 80% of years.

Warmth for growing adds up to 2,693 growing degree days a year (base 50°F), fewer than at 51% of the 49 South Dakota stations. 30% of them (808) have built up by the end of June, and July adds the most, 728. Precipitation totals 18.0 inches a year, most in May (3.0") and least in January (0.4"); May to September bring 60% of it.

The nearest other station, Spearfish, SD, 19 miles south of Belle Fourche and 613 feet higher, has a last frost 2 days later (May 12), a first frost 2 days later (October 2).

The first measurable snow (0.1 inch or more) in Belle Fourche usually arrives around November 15, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Belle Fourche, SD, 6.8 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 27 days after the last snow.

ZIP 57717 is 7 miles from Belle Fourche, SD, which stands at 3,020 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 57717 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.