Frost Dates for 81101 — Alamosa, Colorado

Half of springs at Alamosa 1E, CO see their last 32°F night by May 30; only one in ten is past it by May 17, and one in ten still has one after June 13. Planting tender crops after June 4 leaves a 30% risk of a frost on them, after June 7 20%, and after June 13 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 45% of the 110 Colorado stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 17 in half of years, as early as September 4 one year in ten, and holds off past September 27 one year in ten. A hard freeze of 28°F follows 10 days later, around September 27; in spring the one-in-ten date for 28°F is June 1, 12 days before the 32°F one. The freeze-free season lasts 108 days in a typical year, shorter than at 81% of the 110 Colorado stations; it reaches 126 days one year in ten and falls short of 91 one year in ten. On average 221 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 15 days longer, to about June 14, and return around September 5. Severe cold of 16°F or below comes every winter, usually between October 21 and April 10.

July is the warmest month at Alamosa 1E, CO, averaging 83°F by day and 48°F at night; January is the coldest at 35°F and 0°F. A freezing night is all but certain in every month from September 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 45% of years.

Warmth for growing adds up to 1,533 growing degree days a year (base 50°F), fewer than at 76% of the 110 Colorado stations. 29% of them (443) have built up by the end of June, and July adds the most, 474. Precipitation totals 7.4 inches a year, most in August (1.4") and least in December (0.2"); May to September bring 61% of it.

The nearest other station, Monte Vista 2W, CO, 21 miles west of Alamosa and 155 feet higher, has a last frost 12 days later (June 11), a first frost 4 days earlier (September 13), a season 16 days shorter.

The first measurable snow (0.1 inch or more) in Alamosa usually arrives around October 31, and the last of the season around April 27. Those are the middle dates across the winters of 1991–2020 at Alamosa San Luis Airport, CO, 2.7 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 33 days after the last snow.

ZIP 81101 is 1 mile from Alamosa 1E, CO, which stands at 7,540 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 81101 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.