Frost Dates for 82718 — Gillette, Wyoming

Half of springs at Wright 12W, WY see their last 32°F night by May 25; only one in ten is past it by May 14, and one in ten still has one after June 8. Planting tender crops after May 31 leaves a 30% risk of a frost on them, after June 3 20%, and after June 8 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 23 in half of years, as early as September 8 one year in ten, and holds off past October 5 one year in ten. A hard freeze of 28°F follows 9 days later, around October 2; in spring the one-in-ten date for 28°F is May 26, 13 days before the 32°F one. The freeze-free season lasts 120 days in a typical year, shorter than at 64% of the 33 Wyoming stations; it reaches 138 days one year in ten and falls short of 98 one year in ten. On average 187 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 June 5, and return around September 12. Severe cold of 16°F or below comes every winter, usually between October 27 and April 8.

July is the warmest month at Wright 12W, WY, averaging 86°F by day and 54°F at night; January is the coldest at 34°F and 13°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 26% of years.

Warmth for growing adds up to 2,074 growing degree days a year (base 50°F), fewer than at 52% of the 33 Wyoming stations. 25% of them (518) have built up by the end of June, and July adds the most, 617. Precipitation totals 13.9 inches a year, most in May (2.7") and least in January (0.4"); May to September bring 58% of it.

The nearest other station, Gillette Campbell Airport, WY, 28 miles north of Gillette and 666 feet lower, has a last frost 3 days earlier (May 22), a first frost 2 days later (September 25), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Gillette usually arrives around October 5, and the last of the season around May 8. Those are the middle dates across the winters of 1991–2020 at Wright 12W, WY, 16.9 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 17 days after the last snow.

ZIP 82718 is 17 miles from Wright 12W, WY, which stands at 5,020 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82718 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.