Frost history / Circle, MT
Circle, MT: frost dates by year
Last spring and first fall frost at NOAA station USC00241758, 1964 to 2025, measured from daily minimum temperatures.
Elevation 2,480 ft, 47.412, -105.596. Download the data (JSON), NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | May 15 | Sep 19 |
| Earliest | Apr 20 (1978) | Aug 24 (1992) |
| Latest | Jun 18 (2004) | Oct 10 (1967) |
| Trend | little change (less than half a day per decade) | 1.5 days later per decade |
| Years with data | 61 | 60 |
At 28°F (hard freeze) the median last spring date is May 9 and the median first fall date is Sep 28.
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 2 | Oct 6 | Apr 25 | Oct 6 |
| 2024 | May 4 | Sep 27 | May 4 | Oct 13 |
| 2023 | May 19 | Oct 6 | Apr 30 | Oct 6 |
| 2022 | May 22 | Sep 21 | May 22 | Oct 7 |
| 2021 | May 11 | Sep 17 | May 10 | Oct 20 |
| 2020 | May 12 | no data | May 11 | no data |
| 2019 | May 20 | Oct 1 | May 20 | Oct 9 |
| 2018 | Apr 26 | Sep 28 | Apr 19 | Sep 28 |
| 2017 | May 30 | Sep 25 | Apr 29 | Oct 4 |
| 2016 | May 16 | Sep 13 | May 13 | Sep 13 |
| 2015 | May 21 | Sep 28 | May 19 | Sep 28 |
| 2014 | May 15 | Sep 12 | May 15 | Sep 14 |
| 2013 | May 11 | Oct 5 | May 11 | Oct 5 |
| 2012 | May 12 | Sep 11 | May 11 | Oct 5 |
| 2011 | May 15 | Sep 14 | May 2 | Oct 9 |
| 2010 | May 12 | Sep 17 | May 10 | Oct 16 |
| 2009 | Jun 10 | Sep 22 | Jun 2 | Sep 28 |
| 2008 | May 10 | Sep 8 | May 3 | Oct 9 |
| 2007 | May 30 | Sep 9 | Apr 13 | Sep 14 |
| 2006 | May 15 | Sep 19 | May 11 | Sep 19 |
| 2005 | May 30 | Sep 22 | May 14 | Oct 6 |
| 2004 | Jun 18 | Sep 21 | Jun 18 | Oct 1 |
| 2003 | May 20 | Sep 22 | May 20 | Sep 28 |
| 2002 | May 24 | Sep 22 | May 17 | Sep 22 |
| 2001 | May 23 | Oct 3 | May 3 | Oct 3 |
| 2000 | May 14 | Sep 22 | May 13 | Oct 4 |
| 1999 | May 17 | Sep 14 | May 7 | Sep 14 |
| 1998 | Jun 4 | Oct 7 | Apr 20 | Oct 30 |
| 1997 | May 29 | Sep 19 | May 14 | Sep 19 |
| 1996 | May 11 | Sep 24 | May 9 | Sep 24 |
| 1995 | May 25 | Sep 21 | Apr 29 | Sep 21 |
| 1994 | May 4 | Aug 31 | Apr 30 | Aug 31 |
| 1993 | May 24 | Sep 13 | May 16 | Sep 14 |
| 1992 | Jun 6 | Aug 24 | Apr 22 | Sep 18 |
| 1991 | May 7 | Sep 18 | May 7 | Sep 18 |
| 1990 | May 14 | Sep 22 | May 14 | Oct 7 |
| 1989 | May 2 | no data | May 1 | no data |
| 1988 | May 4 | Aug 28 | May 3 | Oct 5 |
| 1987 | Apr 21 | Sep 19 | Apr 13 | Oct 7 |
| 1986 | no data | Sep 7 | no data | Oct 11 |
| 1985 | Jun 4 | Sep 23 | Apr 22 | Sep 24 |
| 1984 | May 11 | Sep 14 | May 8 | Sep 23 |
| 1983 | Jun 4 | Sep 13 | May 13 | Sep 20 |
| 1982 | May 31 | Sep 19 | Apr 30 | Sep 20 |
| 1981 | May 9 | Sep 16 | May 9 | Sep 27 |
| 1980 | May 14 | Sep 25 | May 12 | Sep 25 |
| 1979 | May 14 | Sep 14 | May 11 | Oct 9 |
| 1978 | Apr 20 | Sep 20 | Apr 20 | Oct 6 |
| 1977 | May 6 | Oct 2 | Apr 24 | Oct 4 |
| 1976 | May 6 | Sep 23 | May 6 | Sep 23 |
| 1975 | May 2 | Sep 12 | Apr 21 | Sep 12 |
| 1974 | May 23 | Sep 2 | May 12 | Sep 2 |
| 1973 | May 16 | Sep 16 | May 14 | Sep 16 |
| 1972 | May 6 | Sep 21 | May 6 | Sep 21 |
| 1971 | May 23 | Sep 18 | Apr 30 | Oct 8 |
| 1970 | May 15 | Sep 12 | May 1 | Sep 12 |
| 1969 | May 11 | Sep 16 | Apr 28 | Oct 8 |
| 1968 | May 20 | Sep 22 | May 20 | Oct 3 |
| 1967 | May 14 | Oct 10 | May 11 | Oct 17 |
| 1966 | May 12 | Sep 14 | May 2 | Sep 14 |
| 1965 | May 27 | Sep 5 | May 27 | Sep 5 |
| 1964 | May 31 | Sep 11 | May 12 | 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.