Frost history / Swan Lake, MT
Swan Lake, MT: frost dates by year
Last spring and first fall frost at NOAA station USC00248087, 1964 to 2025, measured from daily minimum temperatures.
Elevation 3,100 ft, 47.916, -113.839. Download the data (JSON), NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | Jun 8 | Sep 8 |
| Earliest | May 5 (2019) | Aug 7 (1973) |
| Latest | Jul 17 (2006) | Oct 9 (2023) |
| Trend | 5.7 days earlier per decade | 5.2 days later per decade |
| Years with data | 40 | 39 |
At 28°F (hard freeze) the median last spring date is May 14 and the median first fall date is Sep 24.
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 | May 23 | Oct 6 | Apr 25 | Oct 6 |
| 2024 | May 19 | Sep 23 | May 5 | Oct 4 |
| 2023 | May 10 | Oct 9 | Apr 29 | Oct 25 |
| 2022 | May 23 | Sep 11 | May 14 | Oct 18 |
| 2021 | May 20 | Sep 17 | Apr 22 | Oct 8 |
| 2020 | May 17 | no data | Apr 18 | no data |
| 2019 | May 5 | Sep 30 | May 2 | Sep 30 |
| 2018 | May 13 | Sep 20 | Apr 25 | Oct 11 |
| 2011 | Jun 4 | Sep 4 | May 5 | Sep 29 |
| 2010 | May 25 | Sep 23 | May 13 | Oct 12 |
| 2009 | Jun 9 | Sep 9 | May 21 | Sep 28 |
| 2008 | Jun 12 | Sep 8 | May 10 | Oct 9 |
| 2007 | Jun 26 | no data | Jun 26 | no data |
| 2006 | Jul 17 | Sep 1 | May 13 | Sep 18 |
| 2005 | May 26 | Sep 21 | May 2 | Sep 28 |
| 2004 | Jun 16 | Oct 2 | May 24 | Oct 25 |
| 2003 | no data | Sep 10 | no data | Oct 24 |
| 2002 | Jun 7 | Sep 21 | May 12 | Sep 22 |
| 2001 | Jun 5 | Sep 8 | May 21 | Sep 30 |
| 2000 | Jun 1 | Aug 29 | May 13 | Sep 23 |
| 1999 | no data | Sep 1 | no data | Sep 13 |
| 1997 | May 19 | no data | May 8 | no data |
| 1996 | no data | Sep 23 | no data | Sep 24 |
| 1989 | no data | Sep 7 | no data | Sep 11 |
| 1988 | Jun 2 | no data | May 15 | no data |
| 1985 | Jun 25 | Aug 17 | May 14 | Sep 26 |
| 1984 | Jul 7 | Sep 12 | Jun 2 | Sep 12 |
| 1983 | May 20 | no data | May 14 | no data |
| 1982 | Jul 17 | Aug 29 | May 31 | Sep 14 |
| 1981 | May 13 | Sep 3 | May 4 | Sep 24 |
| 1979 | Jul 3 | Sep 12 | Jul 3 | Sep 23 |
| 1978 | Jun 20 | Sep 17 | May 23 | Sep 17 |
| 1977 | May 30 | Sep 2 | May 30 | Sep 25 |
| 1976 | Jun 28 | Aug 17 | May 21 | Sep 8 |
| 1975 | no data | Sep 3 | no data | Sep 19 |
| 1974 | no data | Sep 2 | no data | Sep 2 |
| 1973 | Jul 13 | Aug 7 | Jul 2 | Sep 2 |
| 1972 | Jul 4 | no data | May 4 | no data |
| 1971 | Jul 7 | no data | Jul 7 | no data |
| 1970 | May 31 | Aug 27 | May 12 | Sep 10 |
| 1969 | Jun 15 | Aug 17 | Jun 13 | Sep 6 |
| 1968 | Jun 16 | Sep 21 | May 12 | Oct 2 |
| 1967 | Jun 24 | Aug 25 | May 26 | Sep 23 |
| 1966 | Jun 13 | Aug 12 | May 19 | Sep 30 |
| 1965 | Jun 14 | Aug 31 | Jun 8 | Sep 16 |
| 1964 | Jun 28 | Aug 24 | May 26 | Sep 11 |
"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.