Frost dates / Colorado / Fort Collins

Frost dates in Fort Collins, CO

The station on this page is FT COLLINS, CO US (USC00053005), 2.2 miles from the city point. Population in the Census 2024 estimate is 170,924.

Zone 5bUSDA average annual extreme minimum -15°F to -10°F, from ZIP 80525 (1.9 miles from the city point used on this page).

Median last 32°F is May 2. Median first 32°F is October 7. The 50% growing-season length is 157 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 24	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 7	Median.
90%	October 20	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%	175
50%	157
90%	139

28°F threshold

	10%	50%	90%
Last, on or after	May 5	April 20	April 5
First, on or before	October 2	October 17	October 28
Season at least	198 days	179 days	159 days

36°F threshold

	10%	50%	90%
Last, on or after	May 26	May 12	May 1
First, on or before	September 15	September 29	October 11
Season at least	154 days	138 days	120 days

Station FT COLLINS, CO US (USC00053005). Completeness flag S, 29 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 1525.2 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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Fort Collins, CO

Zone 5bAverage annual extreme minimum -15°F to -10°F

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

Colorado. Nearest qualified station: FT COLLINS, CO US (USC00053005), 2.2 miles. Median last 32°F May 2. Median first 32°F October 7. The 50% growing-season length is 157 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 24	October 7	October 20

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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