Frost Dates for 80808 — Calhan, Colorado

Half of springs at Rush 1N, CO see their last 32°F night by May 9; only one in ten is past it by April 29, and one in ten still has one after May 22. Planting tender crops after May 14 leaves a 30% risk of a frost on them, after May 17 20%, and after May 22 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 67% of the 110 Colorado stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 4 in half of years, as early as September 21 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 8 days later, around October 12; in spring the one-in-ten date for 28°F is May 11, 11 days before the 32°F one. The freeze-free season lasts 146 days in a typical year, longer than at 55% of the 110 Colorado stations; it reaches 163 days one year in ten and falls short of 127 one year in ten. On average 181 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 10 days longer, to about May 19, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 7 and March 30.

July is the warmest month at Rush 1N, CO, averaging 86°F by day and 56°F at night; December is the coldest at 43°F and 16°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 84% of years.

Warmth for growing adds up to 2,462 growing degree days a year (base 50°F), fewer than at 51% of the 110 Colorado stations. 30% of them (747) have built up by the end of June, and July adds the most, 654. Precipitation totals 14.7 inches a year, most in July (2.7") and least in January (0.2"); May to September bring 70% of it.

The nearest other station, Eastonville 2 NNW, CO, 18 miles northwest of Calhan and 1,156 feet higher, has a last frost 20 days later (May 29), a first frost 13 days earlier (September 21), a season 32 days shorter.

The first measurable snow (0.1 inch or more) in Calhan usually arrives around October 29, and the last of the season around May 2. Those are the middle dates across the winters of 1991–2020 at Calhan 3.1 N, CO, 7.3 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 7 days after the last snow.

ZIP 80808 is 15 miles from Rush 1N, CO, which stands at 6,054 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 80808 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.