Frost history / Boulder, CO
Boulder, CO: frost dates by year
Last spring and first fall frost at NOAA station USC00050848, 1951 to 2025, measured from daily minimum temperatures.
Elevation 5,484 ft, 39.992, -105.267. Download the data (JSON), NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | May 2 | Oct 7 |
| Earliest | Apr 4 (2012) | Sep 8 (2020) |
| Latest | Jun 3 (1951) | Oct 31 (1963) |
| Trend | little change (less than half a day per decade) | little change (less than half a day per decade) |
| Years with data | 70 | 70 |
At 28°F (hard freeze) the median last spring date is Apr 21 and the median first fall date is Oct 21.
The trend is a straight-line fit through the years with a freeze. A positive spring trend means the last frost now comes later. Short or patchy records give noisy trends.
Chart
Last spring frost (32°F)
First fall frost (32°F)
Dots are single years. The gray line is the median, the green line the fitted trend.
Year by year
| Year | Last spring 32°F | First fall 32°F | Last spring 28°F | First fall 28°F |
|---|---|---|---|---|
| 2025 | Apr 20 | Oct 19 | Apr 20 | Oct 28 |
| 2024 | Apr 27 | Oct 25 | Apr 21 | Oct 31 |
| 2023 | Apr 28 | Oct 13 | Apr 23 | Oct 27 |
| 2022 | May 22 | Oct 17 | Apr 18 | Oct 28 |
| 2021 | Apr 24 | Oct 14 | Apr 22 | Oct 15 |
| 2020 | Apr 18 | Sep 8 | Apr 18 | Oct 16 |
| 2019 | May 22 | Oct 7 | Apr 14 | Oct 10 |
| 2018 | Apr 25 | Oct 10 | Apr 25 | Oct 14 |
| 2017 | no data | Oct 3 | no data | Oct 10 |
| 2016 | May 2 | Oct 7 | May 2 | Oct 20 |
| 2015 | May 11 | Oct 24 | Apr 4 | Oct 28 |
| 2014 | May 14 | Sep 12 | Apr 15 | Nov 4 |
| 2013 | May 5 | Oct 4 | May 3 | Oct 5 |
| 2012 | Apr 4 | Oct 5 | Mar 21 | Oct 7 |
| 2011 | May 5 | Oct 19 | Apr 4 | Oct 26 |
| 2010 | May 13 | Oct 27 | May 13 | Oct 28 |
| 2009 | no data | Oct 2 | no data | Oct 6 |
| 2008 | May 11 | Oct 13 | May 3 | Oct 13 |
| 2007 | May 6 | Oct 16 | Apr 14 | Oct 22 |
| 2006 | May 11 | Sep 24 | Apr 25 | Oct 18 |
| 2005 | May 3 | Oct 7 | Apr 30 | Oct 31 |
| 2004 | May 1 | Oct 14 | Apr 12 | Nov 1 |
| 2003 | May 11 | Oct 14 | Apr 8 | Oct 26 |
| 2002 | May 24 | Oct 12 | May 9 | Oct 17 |
| 2001 | May 21 | Oct 5 | May 21 | Oct 25 |
| 2000 | May 13 | Sep 23 | May 13 | Sep 25 |
| 1999 | May 17 | Sep 28 | May 6 | Sep 29 |
| 1998 | Apr 29 | Oct 17 | Apr 17 | Oct 18 |
| 1997 | May 3 | Oct 9 | Apr 27 | Oct 24 |
| 1996 | Apr 29 | Sep 26 | Apr 29 | Sep 27 |
| 1995 | May 24 | Sep 20 | Apr 27 | Sep 22 |
| 1994 | May 4 | Sep 22 | Apr 28 | Oct 25 |
| 1993 | May 2 | no data | Apr 21 | no data |
| 1992 | Apr 25 | Oct 8 | Apr 1 | Oct 8 |
| 1991 | May 3 | Oct 4 | Apr 14 | Oct 5 |
| 1990 | no data | Oct 8 | no data | Oct 8 |
| 1989 | May 1 | no data | May 1 | no data |
| 1988 | May 3 | Oct 23 | May 3 | Oct 28 |
| 1987 | Apr 21 | Oct 10 | Apr 21 | Oct 10 |
| 1986 | Apr 19 | Oct 4 | Apr 15 | Oct 11 |
| 1985 | May 14 | Sep 23 | Apr 8 | Sep 28 |
| 1984 | Apr 30 | Sep 25 | Apr 30 | Sep 30 |
| 1983 | no data | Sep 20 | no data | Sep 21 |
| 1982 | May 6 | no data | May 6 | no data |
| 1981 | May 10 | Oct 18 | Apr 5 | Oct 23 |
| 1980 | Apr 25 | Oct 16 | Apr 13 | Oct 24 |
| 1978 | May 6 | no data | Apr 19 | no data |
| 1977 | Apr 21 | Oct 1 | Apr 4 | Oct 11 |
| 1976 | May 1 | Sep 28 | Apr 18 | Oct 7 |
| 1975 | May 1 | Oct 1 | Apr 18 | Oct 23 |
| 1974 | Apr 30 | Sep 12 | Apr 16 | Nov 4 |
| 1973 | May 3 | Oct 10 | May 2 | Nov 2 |
| 1972 | May 2 | Oct 15 | May 2 | Oct 29 |
| 1971 | Apr 27 | Sep 17 | Apr 6 | Sep 19 |
| 1970 | May 1 | Sep 25 | Apr 20 | Oct 7 |
| 1969 | Apr 28 | Oct 4 | Mar 27 | Oct 11 |
| 1968 | May 17 | Oct 17 | Apr 23 | Oct 27 |
| 1967 | May 14 | Oct 16 | Apr 26 | Oct 27 |
| 1966 | May 13 | Oct 1 | May 12 | Oct 15 |
| 1965 | May 9 | Sep 17 | Mar 26 | Sep 17 |
| 1964 | Apr 18 | Oct 19 | Apr 8 | Oct 19 |
| 1963 | Apr 23 | Oct 31 | Apr 3 | Nov 2 |
| 1962 | Apr 12 | Oct 25 | Apr 2 | Oct 25 |
| 1961 | Apr 27 | Sep 25 | Apr 25 | Oct 25 |
| 1960 | May 19 | Oct 30 | Apr 30 | Oct 30 |
| 1959 | Apr 21 | Sep 28 | Apr 21 | Sep 29 |
| 1958 | Apr 30 | Oct 1 | Apr 29 | Oct 30 |
| 1957 | May 17 | Oct 25 | Apr 26 | Oct 26 |
| 1956 | Apr 10 | Oct 24 | Apr 9 | Nov 1 |
| 1955 | Apr 28 | Oct 23 | Apr 13 | Oct 23 |
| 1954 | May 3 | Oct 14 | May 3 | Oct 27 |
| 1953 | May 13 | Oct 26 | May 13 | Nov 9 |
| 1952 | Apr 22 | Oct 7 | Apr 9 | Oct 15 |
| 1951 | Jun 3 | Sep 21 | Apr 21 | Oct 22 |
"none" means the station recorded no freeze at that threshold in that half of the year. "no data" means more than 10% of the season's daily readings were missing. Years with no usable data are left out. See the methodology for the rules, and the ZIP lookup for 1991 to 2020 frost probabilities.