Boulder County, Colorado · Frost dates
Boulder County frost dates.
First-frost, last-frost, and growing-season length for Boulder County, Colorado. Sourced from NOAA 1991-2020 Climate Normals.
Data confidence: high · USDA zone: 5a
32°F — light freeze
Last spring frost
- 10%
- 07-04
- 20%
- 06-30
- 50%
- 06-21
- 80%
- 06-12
- 90%
- 06-07
First fall frost
- 10%
- 08-17
- 20%
- 08-24
- 50%
- 09-02
- 80%
- 09-10
- 90%
- 09-15
28°F — killing freeze
Last spring freeze
- 10%
- 06-20
- 20%
- 06-15
- 50%
- 06-04
- 80%
- 05-26
- 90%
- 05-22
First fall freeze
- 10%
- 09-02
- 20%
- 09-05
- 50%
- 09-14
- 80%
- 09-23
- 90%
- 09-27
Growing season length (days, 28°F threshold)
- Short year
- 74
- Median
- 102
- Long year
- 128
Source NOAA station
BOULDER 14 W, CO US
8.6 mi · 30 yrs of record (1991–2020) · 9828 ft elev.
Data from BOULDER 14 W, CO US, 8.6 miles away with 30-year NOAA record (1991-2020).
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