Frost history / Boulder, MT
Boulder, MT: frost dates by year
Last spring and first fall frost at NOAA station USC00241008, 1951 to 2024, measured from daily minimum temperatures.
Elevation 4,904 ft, 46.231, -112.114. Download the data (JSON), NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | Jun 11 | Sep 5 |
| Earliest | May 11 (2015) | Aug 9 (1995) |
| Latest | Jul 20 (1993) | Sep 27 (1966) |
| Trend | little change (less than half a day per decade) | 0.5 days later per decade |
| Years with data | 63 | 64 |
At 28°F (hard freeze) the median last spring date is May 23 and the median first fall date is Sep 15.
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 |
|---|---|---|---|---|
| 2024 | Jun 16 | Sep 22 | May 20 | Sep 22 |
| 2017 | Jun 11 | Sep 16 | May 19 | Sep 17 |
| 2016 | Jun 17 | Aug 25 | May 11 | Oct 6 |
| 2015 | May 11 | Sep 18 | May 11 | Oct 5 |
| 2014 | May 20 | Sep 5 | May 14 | Sep 12 |
| 2013 | Jun 3 | Sep 25 | May 5 | Sep 27 |
| 2012 | no data | Aug 27 | no data | Oct 4 |
| 2011 | Jun 16 | no data | May 28 | no data |
| 2010 | May 30 | Sep 2 | May 22 | Oct 12 |
| 2009 | Jun 23 | Sep 13 | May 22 | Sep 21 |
| 2008 | Jun 11 | Sep 8 | May 30 | Sep 11 |
| 2007 | May 26 | Sep 11 | May 4 | Sep 11 |
| 2006 | May 30 | Aug 31 | May 5 | Sep 1 |
| 2005 | Jun 13 | Aug 31 | May 3 | Sep 12 |
| 2004 | Jun 16 | Sep 3 | May 25 | Sep 21 |
| 2003 | Jun 23 | Sep 14 | Jun 23 | Sep 14 |
| 2002 | May 25 | Aug 17 | May 23 | Sep 22 |
| 2001 | Jun 5 | Sep 20 | May 21 | Oct 5 |
| 2000 | Jun 2 | Sep 3 | May 10 | Sep 7 |
| 1999 | Jul 5 | Sep 4 | Jun 10 | Sep 12 |
| 1998 | Jun 5 | Sep 21 | Jun 5 | Sep 22 |
| 1997 | May 19 | Sep 17 | May 19 | Sep 17 |
| 1996 | Jun 18 | Sep 6 | May 21 | Sep 6 |
| 1995 | Jun 20 | Aug 9 | May 27 | Sep 21 |
| 1994 | Jun 17 | Aug 23 | Jun 15 | Sep 5 |
| 1993 | Jul 20 | Aug 27 | May 20 | Aug 30 |
| 1992 | Jun 4 | Aug 22 | May 16 | Aug 23 |
| 1991 | Jun 18 | Sep 18 | May 27 | Sep 18 |
| 1990 | Jun 8 | Sep 22 | May 19 | Oct 7 |
| 1989 | May 31 | Sep 4 | May 31 | Sep 7 |
| 1988 | May 20 | Sep 11 | May 20 | Sep 13 |
| 1987 | Jun 3 | Aug 12 | Jun 3 | Sep 17 |
| 1986 | Jul 6 | Sep 16 | May 23 | Sep 22 |
| 1985 | May 31 | Aug 17 | May 13 | Sep 20 |
| 1984 | Jun 12 | Sep 11 | May 25 | Sep 13 |
| 1983 | Jun 20 | Sep 6 | May 31 | Sep 10 |
| 1982 | Jun 5 | Sep 11 | May 31 | Sep 11 |
| 1981 | Jul 8 | Aug 31 | May 9 | Sep 20 |
| 1980 | May 15 | Sep 16 | Apr 16 | Sep 22 |
| 1979 | Jun 9 | Sep 11 | Jun 1 | Sep 11 |
| 1978 | Jun 20 | Sep 16 | Jun 11 | Sep 17 |
| 1977 | May 30 | Aug 28 | May 30 | Sep 18 |
| 1976 | May 26 | Aug 27 | May 26 | Oct 5 |
| 1975 | Jun 28 | Sep 3 | May 26 | Sep 19 |
| 1974 | Jun 1 | Sep 2 | May 16 | Sep 2 |
| 1973 | Jun 19 | Sep 14 | Jun 19 | Sep 15 |
| 1972 | Jun 19 | Sep 7 | May 10 | Sep 24 |
| 1971 | Jun 29 | Sep 16 | May 24 | Sep 18 |
| 1970 | Jun 11 | Sep 10 | May 2 | Sep 11 |
| 1969 | Jun 14 | Aug 30 | Jun 14 | Sep 4 |
| 1967 | May 26 | Sep 14 | May 26 | Oct 4 |
| 1966 | Jun 13 | Sep 27 | Jun 13 | Sep 30 |
| 1964 | no data | Sep 4 | no data | Sep 11 |
| 1963 | Jun 22 | Sep 16 | May 21 | Oct 15 |
| 1962 | Jun 7 | Aug 30 | Jun 7 | Aug 30 |
| 1961 | May 19 | Sep 2 | May 7 | Sep 13 |
| 1960 | Jun 24 | Aug 24 | May 24 | Aug 24 |
| 1959 | Jun 10 | Sep 2 | May 29 | Sep 9 |
| 1958 | May 15 | Sep 3 | May 6 | Sep 3 |
| 1957 | May 24 | Sep 9 | May 24 | Sep 9 |
| 1956 | May 13 | Aug 31 | May 13 | Sep 5 |
| 1955 | no data | Sep 18 | no data | Sep 19 |
| 1954 | Jun 18 | no data | Jun 18 | no data |
| 1953 | Jun 26 | Aug 24 | May 24 | Sep 4 |
| 1952 | Jun 13 | Sep 1 | May 10 | Sep 14 |
| 1951 | Jun 3 | Sep 2 | Jun 3 | Sep 2 |
"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.