Frost dates / Colorado / Broomfield

Frost dates in Broomfield, CO

The station on this page is NORTHGLENN, CO US (USC00055984), 4.3 miles from the city point. Population in the Census 2024 estimate is 78,323.

Zone 6aUSDA average annual extreme minimum -10°F to -5°F, from ZIP 80020 (2 miles from the city point used on this page).

Median last 32°F is May 2. Median first 32°F is October 11. The 50% growing-season length is 160 days. The green band runs from the median last frost to the median first frost. Thin ticks mark the 10%, 50%, and 90% dates.

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Last 32°F in spring

NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.

Probability	Date	How to read it
90%	April 18	Earlier date. A last 32°F on or after this day is common.
50%	May 2	Median.
10%	May 14	Later date. A last 32°F on or after this day is uncommon.

First 32°F in fall

NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.

Probability	Date	How to read it
10%	September 26	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 11	Median.
90%	October 24	Later date. A first 32°F on or before this day is common.

32°F growing-season length

Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.

Probability the season is at least this long	Days
10%	180
50%	160
90%	142

28°F threshold

	10%	50%	90%
Last, on or after	May 5	April 20	April 4
First, on or before	October 7	October 21	November 4
Season at least	204 days	182 days	160 days

36°F threshold

	10%	50%	90%
Last, on or after	May 26	May 12	April 30
First, on or before	September 18	October 1	October 14
Season at least	159 days	142 days	122 days

Station NORTHGLENN, CO US (USC00055984). Completeness flag S, 26 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 100%. Freeze dates are conditional on that threshold occurring. Elevation 1648.1 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.

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Broomfield, CO

Zone 6aAverage annual extreme minimum -10°F to -5°F

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Colorado. Nearest qualified station: NORTHGLENN, CO US (USC00055984), 4.3 miles. Median last 32°F May 2. Median first 32°F October 11. The 50% growing-season length is 160 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 14	May 2	April 18
First 32°F on or before	September 26	October 11	October 24

Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.

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Planting calendar

Frost dates for Colorado are above. Planting windows appear for states with a cited extension guide. The fall and seed tools use the numbers you enter and the station dates.

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