Frost history / Westby, MT
Westby, MT: frost dates by year
Last spring and first fall frost at NOAA station USC00248777, 1951 to 2025, measured from daily minimum temperatures.
Elevation 2,103 ft, 48.874, -104.050. Download the data (JSON) · NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | May 15 | Sep 19 |
| Earliest | Apr 21 (1978) | Aug 20 (2004) |
| Latest | Jun 13 (1969) | Oct 9 (1979) |
| Trend | little change (less than half a day per decade) | 0.9 days later per decade |
| Years with data | 51 | 53 |
At 28°F (hard freeze) the median last spring date is May 7 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 6 | Oct 6 | Apr 25 | Oct 6 |
| 2024 | May 2 | Oct 1 | Apr 22 | Oct 6 |
| 2023 | May 20 | Oct 5 | May 2 | Oct 25 |
| 2022 | no data | Oct 7 | no data | Oct 7 |
| 2021 | May 11 | Sep 24 | May 10 | Oct 15 |
| 2020 | no data | Sep 8 | no data | Sep 8 |
| 2016 | May 15 | Sep 13 | May 1 | Sep 13 |
| 2015 | no data | Sep 29 | no data | Oct 16 |
| 2011 | May 14 | Sep 14 | May 12 | Oct 9 |
| 2010 | May 13 | Sep 18 | May 10 | Sep 18 |
| 2009 | Jun 10 | Oct 6 | May 16 | Oct 8 |
| 2008 | May 27 | Sep 14 | May 11 | Oct 9 |
| 2007 | May 26 | Sep 14 | Apr 22 | Sep 14 |
| 2006 | May 12 | no data | May 11 | no data |
| 2005 | May 15 | Sep 18 | May 15 | Sep 28 |
| 2004 | no data | Aug 20 | no data | Sep 21 |
| 2003 | May 20 | Sep 14 | May 20 | Sep 30 |
| 2002 | May 24 | Sep 22 | May 24 | Sep 25 |
| 2001 | May 21 | Sep 23 | May 4 | Oct 4 |
| 2000 | Jun 2 | Sep 22 | May 13 | Sep 23 |
| 1999 | May 11 | Sep 14 | Apr 23 | Sep 27 |
| 1998 | Jun 4 | Sep 21 | May 2 | Oct 1 |
| 1997 | May 20 | Sep 19 | May 19 | Oct 13 |
| 1996 | May 13 | Sep 24 | May 13 | Oct 2 |
| 1992 | May 26 | no data | May 25 | no data |
| 1991 | May 7 | Sep 18 | May 6 | Sep 19 |
| 1990 | no data | Oct 6 | no data | Oct 7 |
| 1984 | no data | Sep 4 | no data | Sep 23 |
| 1983 | May 16 | Sep 19 | May 15 | Sep 21 |
| 1982 | May 9 | Sep 13 | May 7 | Sep 15 |
| 1981 | no data | Sep 3 | no data | Sep 16 |
| 1980 | May 14 | no data | May 13 | no data |
| 1979 | May 11 | Oct 9 | May 11 | Oct 13 |
| 1978 | Apr 21 | Oct 6 | Apr 21 | Oct 6 |
| 1977 | May 6 | Oct 2 | May 1 | Oct 2 |
| 1976 | May 7 | no data | May 7 | no data |
| 1975 | Apr 30 | Sep 12 | Apr 30 | Oct 15 |
| 1974 | May 24 | Sep 2 | May 3 | Sep 29 |
| 1973 | May 16 | Sep 15 | Apr 27 | Sep 16 |
| 1972 | May 9 | Sep 21 | May 6 | Sep 21 |
| 1971 | May 19 | Sep 18 | Apr 28 | Sep 18 |
| 1970 | May 14 | Sep 12 | May 1 | Sep 13 |
| 1969 | Jun 13 | Sep 16 | Apr 28 | Oct 8 |
| 1968 | May 20 | Oct 3 | May 11 | Oct 3 |
| 1967 | May 12 | Sep 27 | May 11 | Oct 10 |
| 1966 | May 12 | Sep 14 | May 9 | Oct 4 |
| 1965 | May 27 | Sep 5 | May 27 | Sep 5 |
| 1964 | Jun 1 | Sep 7 | Apr 30 | Sep 11 |
| 1963 | May 22 | Oct 8 | May 22 | Oct 27 |
| 1962 | May 8 | Sep 3 | Apr 17 | Sep 9 |
| 1961 | May 18 | Sep 23 | May 1 | Sep 24 |
| 1960 | May 7 | Sep 17 | May 7 | Sep 17 |
| 1957 | May 9 | no data | Apr 27 | no data |
| 1956 | no data | Sep 4 | no data | Sep 4 |
| 1955 | Apr 26 | no data | Apr 26 | no data |
| 1954 | May 31 | Sep 21 | May 5 | Sep 21 |
| 1953 | May 16 | Sep 21 | May 16 | Sep 21 |
| 1952 | May 28 | Sep 22 | May 28 | Oct 4 |
| 1951 | Jun 1 | Sep 23 | Jun 1 | Sep 23 |
"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 1991–2020 frost probabilities.