Frost Dates for 57718 — Black Hawk, South Dakota

Half of springs at Rapid City 4NW, 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 15 leaves a 30% risk of a frost on them, after May 19 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 October 5 in half of years, as early as September 20 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 10 days later, around October 15; in spring the one-in-ten date for 28°F is May 11, 14 days before the 32°F one. The freeze-free season lasts 147 days in a typical year, shorter than at 59% of the 49 South Dakota stations; it reaches 166 days one year in ten and falls short of 127 one year in ten. On average 170 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 27. Severe cold of 16°F or below comes every winter, usually between November 8 and March 31.

July is the warmest month at Rapid City 4NW, SD, averaging 84°F by day and 58°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 82% of years.

Warmth for growing adds up to 2,317 growing degree days a year (base 50°F), fewer than at 92% of the 49 South Dakota stations. 27% of them (629) have built up by the end of June, and July adds the most, 648. Precipitation totals 18.8 inches a year, most in May (3.7") and least in January (0.2"); May to September bring 69% of it.

The nearest other station, Johnson Siding, SD, 8 miles southwest of Black Hawk and 705 feet higher, has a last frost 10 days later (May 20), a first frost 10 days earlier (September 25), a season 21 days shorter.

The first measurable snow (0.1 inch or more) in Black Hawk usually arrives around November 11, and the last of the season around April 19. Those are the middle dates across the winters of 1991–2020 at Rapid City 4NW, SD, 4.4 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 21 days after the last snow.

ZIP 57718 is 4 miles from Rapid City 4NW, SD, which stands at 3,479 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 57718 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.