Thornton, CO 80602 Frost Dates
Frost dates for Thornton, CO, ZIP 80602
The last spring frost here typically falls around 05/03, about 248 days from today. The first fall frost typically arrives around 10/07, about 155 frost-free days later.
Thornton sits in USDA Zone 6a (-10 to -5°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
What to do before the first frost
Zone 6a around Thornton has about 6 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
Why 05/03 isn't a guarantee
05/03 is the middle of 30 years of NOAA records, not a promise. Plant by 04/22 and you're betting against frost in roughly 9 years out of 10. 05/16 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Thornton compares
About 155 days separate Thornton's last and first frost, putting it 33,900 of 40,283 ZIP codes nationally. Within CO, it ranks 240 of 624.
Learn more
zone vs. frost date explains why Zone 6a and Thornton's frost date answer different questions, and the frost range explains how to read the range around Thornton's dates instead of trusting one.