Frost Dates for 81611 — Aspen, Colorado

Half of springs at Aspen 1SW, CO see their last 32°F night by June 2; only one in ten is past it by May 17, and one in ten still has one after June 17. Planting tender crops after June 8 leaves a 30% risk of a frost on them, after June 12 20%, and after June 17 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 56% of the 110 Colorado 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 12 one year in ten, and holds off past October 4 one year in ten. A hard freeze of 28°F follows 8 days later, around October 1; in spring the one-in-ten date for 28°F is June 5, 12 days before the 32°F one. The freeze-free season lasts 113 days in a typical year, shorter than at 74% of the 110 Colorado stations; it reaches 131 days one year in ten and falls short of 92 one year in ten. On average 210 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 16, and return around September 14. Severe cold of 16°F or below comes every winter, usually between October 29 and April 9.

July is the warmest month at Aspen 1SW, CO, averaging 76°F by day and 48°F at night; January is the coldest at 32°F and 10°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 56% of years.

Warmth for growing adds up to 1,109 growing degree days a year (base 50°F), fewer than at 88% of the 110 Colorado stations. 24% of them (267) have built up by the end of June, and July adds the most, 367. Precipitation totals 24.6 inches a year, most in April (2.7") and least in June (1.1"); May to September bring 37% of it.

The nearest other station, Aspen Pitkin Co Airport, CO, 3 miles northwest of Aspen and 455 feet lower, has a last frost 2 days earlier (May 31), the same first-frost date, a season 1 day longer.

The first measurable snow (0.1 inch or more) in Aspen usually arrives around October 7, and the last of the season around May 14. Those are the middle dates across the winters of 1991–2020 at Aspen 1SW, CO, 1.3 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 19 days after the last snow.

ZIP 81611 is 1 mile from Aspen 1SW, CO, which stands at 8,175 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 81611 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.