Frost Dates for 82721 — Moorcroft, Wyoming

Half of springs at Devils Twr #2, WY see their last 32°F night by May 23; only one in ten is past it by May 12, and one in ten still has one after June 6. Planting tender crops after May 28 leaves a 30% risk of a frost on them, after May 31 20%, and after June 6 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 58% of the 33 Wyoming stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 20 in half of years, as early as September 4 one year in ten, and holds off past October 4 one year in ten. A hard freeze of 28°F follows 11 days later, around October 1; in spring the one-in-ten date for 28°F is May 24, 13 days before the 32°F one. The freeze-free season lasts 118 days in a typical year, shorter than at 70% of the 33 Wyoming stations; it reaches 137 days one year in ten and falls short of 95 one year in ten. On average 201 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 12 days longer, to about June 4, and return around September 8. Severe cold of 16°F or below comes every winter, usually between October 29 and April 9.

July is the warmest month at Devils Twr #2, WY, averaging 85°F by day and 55°F at night; January is the coldest at 34°F and 8°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 19% of years.

Warmth for growing adds up to 2,120 growing degree days a year (base 50°F), more than at 52% of the 33 Wyoming stations. 27% of them (580) have built up by the end of June, and July adds the most, 620. Precipitation totals 19.0 inches a year, most in June (3.2") and least in January (0.7"); May to September bring 60% of it.

The nearest other station, Sundance, WY, 28 miles east of Moorcroft and 833 feet higher, has a last frost 2 days earlier (May 21), a first frost 5 days later (September 25), a season 6 days longer.

The first measurable snow (0.1 inch or more) in Moorcroft usually arrives around November 1, and the last of the season around April 11. Those are the middle dates across the winters of 1991–2020 at Devils Twr #2, WY, 13.6 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 42 days after the last snow.

ZIP 82721 is 14 miles from Devils Twr #2, WY, which stands at 3,862 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82721 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.