Frost Dates for 80603 — Brighton, Colorado

Half of springs at Denver International Airport, CO see their last 32°F night by May 5; only one in ten is past it by April 23, and one in ten still has one after May 19. Planting tender crops after May 11 leaves a 30% risk of a frost on them, after May 15 20%, and after May 19 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 October 9 in half of years, as early as September 27 one year in ten, and holds off past October 20 one year in ten. A hard freeze of 28°F follows 9 days later, around October 18; in spring the one-in-ten date for 28°F is May 9, 10 days before the 32°F one. The freeze-free season lasts 156 days in a typical year, longer than at 73% of the 110 Colorado stations; it reaches 173 days one year in ten and falls short of 137 one year in ten. On average 156 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 11 days longer, to about May 16, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 12 and March 21.

July is the warmest month at Denver International Airport, CO, averaging 90°F by day and 60°F at night; December is the coldest at 44°F and 18°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 68% of years.

Warmth for growing adds up to 3,044 growing degree days a year (base 50°F), more than at 79% of the 110 Colorado stations. 31% of them (929) have built up by the end of June, and July adds the most, 776. Precipitation totals 14.6 inches a year, most in May (2.2") and least in January (0.4"); May to September bring 63% of it.

The nearest other station, Brighton 3 SE, CO, 11 miles west of Brighton and 398 feet lower, has a last frost 2 days earlier (May 3), a first frost 2 days earlier (October 7), a season 1 day shorter.

The first measurable snow (0.1 inch or more) in Brighton usually arrives around October 25, and the last of the season around May 1. Those are the middle dates across the winters of 1991–2020 at Hudson 4.8 WSW, CO, 8.6 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 4 days after the last snow.

ZIP 80603 is 8 miles from Denver International Airport, CO, which stands at 5,414 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 80249 (Denver). The 2023 USDA Plant Hardiness Zone Map lists ZIP 80603 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.