Frost Dates for 82901 — Rock Springs, Wyoming

Half of springs at Rock Springs Fire Dept, WY see their last 32°F night by May 24; only one in ten is past it by May 8, and one in ten still has one after June 9. Planting tender crops after May 31 leaves a 30% risk of a frost on them, after June 3 20%, and after June 9 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 55% of the 33 Wyoming stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 24 in half of years, as early as September 9 one year in ten, and holds off past October 4 one year in ten. A hard freeze of 28°F follows 9 days later, around October 3; in spring the one-in-ten date for 28°F is May 26, 14 days before the 32°F one. The freeze-free season lasts 121 days in a typical year, shorter than at 61% of the 33 Wyoming stations; it reaches 141 days one year in ten and falls short of 99 one year in ten. On average 184 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 June 6, and return around September 14. Severe cold of 16°F or below comes every winter, usually between November 5 and March 24.

July is the warmest month at Rock Springs Fire Dept, WY, averaging 86°F by day and 53°F at night; December is the coldest at 33°F and 12°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 28% of years.

Warmth for growing adds up to 1,970 growing degree days a year (base 50°F), fewer than at 64% of the 33 Wyoming stations. 26% of them (515) have built up by the end of June, and July adds the most, 601. Precipitation totals 10.5 inches a year, most in May (1.9") and least in February (0.4"); May to September bring 54% of it.

The nearest other station, Green Rvr, WY, 17 miles west of Rock Springs, has the same 50% last-frost date, a first frost 2 days earlier (September 22), a season 1 day shorter.

The first measurable snow (0.1 inch or more) in Rock Springs usually arrives around November 4, and the last of the season around April 23. Those are the middle dates across the winters of 1991–2020 at Rock Springs Fire Dept, WY, 4.1 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 31 days after the last snow.

ZIP 82901 is 4 miles from Rock Springs Fire Dept, WY, which stands at 6,270 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82901 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.