Frost Dates for 82443 — Thermopolis, Wyoming

Half of springs at Thermopolis, WY see their last 32°F night by May 5; only one in ten is past it by April 23, and one in ten still has one after May 19. Planting tender crops after May 11 leaves a 30% risk of a frost on them, after May 14 20%, and after May 19 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 October 5 in half of years, as early as September 23 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 8, 11 days before the 32°F one. The freeze-free season lasts 152 days in a typical year, the longest of the 33 Wyoming stations; it reaches 168 days one year in ten and falls short of 134 one year in ten. On average 168 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 14 days longer, to about May 19, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 8 and March 17.

July is the warmest month at Thermopolis, WY, averaging 92°F by day and 57°F at night; January is the coldest at 37°F and 12°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 2,780 growing degree days a year (base 50°F), the most of the 33 Wyoming stations. 30% of them (830) have built up by the end of June, and July adds the most, 758. Precipitation totals 12.0 inches a year, most in May (2.5") and least in January (0.4"); May to September bring 53% of it.

The nearest other station, Worland, WY, 28 miles northeast of Thermopolis and 263 feet lower, has a last frost 1 day earlier (May 4), a first frost 4 days earlier (October 1), a season 3 days shorter.

The first measurable snow (0.1 inch or more) in Thermopolis usually arrives around November 6, and the last of the season around April 2. Those are the middle dates across the winters of 1991–2020 at Thermopolis, WY, 6.6 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 33 days after the last snow.

ZIP 82443 is 7 miles from Thermopolis, WY, which stands at 4,321 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82443 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.