Frost Dates for 82604 — Casper, Wyoming

Half of springs at Casper Natrona Co Airport, WY see their last 32°F night by May 26; only one in ten is past it by May 12, and one in ten still has one after June 10. Planting tender crops after June 1 leaves a 30% risk of a frost on them, after June 4 20%, and after June 10 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 48% of the 33 Wyoming stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 22 in half of years, as early as September 5 one year in ten, and holds off past October 4 one year in ten. A hard freeze of 28°F follows 10 days later, around October 2; in spring the one-in-ten date for 28°F is May 27, 14 days before the 32°F one. The freeze-free season lasts 117 days in a typical year, shorter than at 76% of the 33 Wyoming stations; it reaches 136 days one year in ten and falls short of 96 one year in ten. On average 183 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 June 9, and return around September 9. Severe cold of 16°F or below comes every winter, usually between October 31 and April 5.

July is the warmest month at Casper Natrona Co Airport, WY, averaging 89°F by day and 53°F at night; December is the coldest at 35°F and 15°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 32% of years.

Warmth for growing adds up to 2,156 growing degree days a year (base 50°F), more than at 58% of the 33 Wyoming stations. 26% of them (553) have built up by the end of June, and July adds the most, 651. Precipitation totals 12.2 inches a year, most in May (2.2") and least in January (0.5"); May to September bring 53% of it.

The nearest other station, Casper Wwtp, WY, 13 miles east of Casper and 241 feet lower, has a last frost 16 days earlier (May 10), a first frost 7 days later (September 29), a season 21 days longer.

The first measurable snow (0.1 inch or more) in Casper usually arrives around October 4, and the last of the season around May 8. Those are the middle dates across the winters of 1991–2020 at Casper Natrona Co Airport, WY, 8.3 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 18 days after the last snow.

ZIP 82604 is 8 miles from Casper Natrona Co Airport, WY, which stands at 5,338 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82604 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.