Frost Dates for 82601 — Casper, Wyoming

Half of springs at Casper Wwtp, WY see their last 32°F night by May 10; only one in ten is past it by April 30, and one in ten still has one after May 24. Planting tender crops after May 16 leaves a 30% risk of a frost on them, after May 19 20%, and after May 24 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 29 in half of years, as early as September 14 one year in ten, and holds off past October 12 one year in ten. A hard freeze of 28°F follows 7 days later, around October 6; in spring the one-in-ten date for 28°F is May 14, 10 days before the 32°F one. The freeze-free season lasts 138 days in a typical year, longer than at 73% of the 33 Wyoming stations; it reaches 155 days one year in ten and falls short of 118 one year in ten. On average 163 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 13 days longer, to about May 23, and return around September 19. Severe cold of 16°F or below comes every winter, usually between November 4 and March 26.

July is the warmest month at Casper Wwtp, WY, averaging 88°F by day and 56°F at night; January is the coldest at 38°F and 17°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 89% of years.

Warmth for growing adds up to 2,405 growing degree days a year (base 50°F), more than at 82% of the 33 Wyoming stations. 28% of them (670) have built up by the end of June, and July adds the most, 692. Precipitation totals 13.6 inches a year, most in May (2.7") and least in January (0.4"); May to September bring 56% of it.

The nearest other station, Casper 1SW, WY, 3 miles south of Casper, has a last frost 2 days later (May 12), a first frost 2 days later (October 1), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Casper usually arrives around October 17, and the last of the season around April 28. Those are the middle dates across the winters of 1991–2020 at Casper Wwtp, WY, 2.5 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 12 days after the last snow.

ZIP 82601 is 3 miles from Casper Wwtp, WY, which stands at 5,097 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82601 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.