Frost history / Zortman, MT
Zortman, MT: frost dates by year
Last spring and first fall frost at NOAA station USC00249900, 1966 to 2023, measured from daily minimum temperatures.
Elevation 4,035 ft, 47.919, -108.524. Download the data (JSON), NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | May 20 | Sep 19 |
| Earliest | Apr 24 (1978) | Aug 25 (1992) |
| Latest | Jun 18 (2004) | Oct 15 (1967) |
| Trend | little change (less than half a day per decade) | 0.7 days later per decade |
| Years with data | 35 | 36 |
At 28°F (hard freeze) the median last spring date is May 12 and the median first fall date is Sep 25.
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 |
|---|---|---|---|---|
| 2023 | Apr 29 | Oct 6 | Apr 24 | Oct 6 |
| 2022 | May 23 | Sep 21 | May 22 | Oct 24 |
| 2021 | May 24 | Oct 11 | May 24 | Oct 13 |
| 2020 | May 14 | Sep 8 | May 11 | Sep 8 |
| 2019 | May 20 | Sep 28 | May 18 | Sep 29 |
| 2018 | May 2 | Sep 28 | Apr 14 | Sep 28 |
| 2017 | no data | Sep 20 | no data | Sep 20 |
| 2016 | May 15 | Sep 13 | May 14 | Sep 13 |
| 2015 | May 20 | Oct 4 | May 19 | Oct 28 |
| 2014 | May 11 | Sep 10 | May 11 | Sep 11 |
| 2013 | May 11 | Sep 27 | May 2 | Oct 5 |
| 2012 | May 29 | no data | May 11 | no data |
| 2011 | May 15 | Oct 9 | May 14 | Oct 14 |
| 2010 | May 30 | no data | May 9 | no data |
| 2009 | Jun 10 | Sep 28 | May 16 | Sep 28 |
| 2008 | Jun 11 | Sep 8 | Jun 11 | Oct 9 |
| 2007 | May 28 | Sep 14 | Apr 22 | Sep 14 |
| 2006 | May 11 | Sep 16 | May 5 | Oct 9 |
| 2005 | May 30 | Sep 12 | May 14 | Sep 28 |
| 2004 | Jun 18 | Sep 21 | May 14 | Sep 21 |
| 2003 | no data | Sep 17 | no data | Sep 18 |
| 2002 | May 24 | Sep 22 | May 23 | Sep 23 |
| 2001 | no data | Oct 3 | no data | Oct 5 |
| 1993 | Jun 4 | Aug 27 | Apr 26 | Aug 27 |
| 1992 | no data | Aug 25 | no data | Sep 18 |
| 1985 | Jun 3 | no data | Apr 23 | no data |
| 1984 | no data | Sep 13 | no data | Sep 22 |
| 1979 | Jun 8 | no data | May 10 | no data |
| 1978 | Apr 24 | Sep 19 | Apr 20 | Sep 20 |
| 1977 | May 29 | Oct 2 | May 18 | Oct 4 |
| 1976 | May 19 | Sep 19 | May 3 | Sep 19 |
| 1975 | May 29 | Sep 12 | May 2 | Sep 20 |
| 1974 | no data | Sep 3 | no data | Sep 13 |
| 1973 | May 2 | no data | May 1 | no data |
| 1972 | May 12 | Sep 21 | May 7 | Sep 21 |
| 1971 | May 18 | Sep 16 | May 18 | Sep 19 |
| 1970 | May 14 | Sep 11 | May 13 | Sep 12 |
| 1969 | Jun 11 | Sep 15 | May 21 | Oct 5 |
| 1968 | May 30 | Sep 21 | May 30 | Oct 3 |
| 1967 | May 14 | Oct 15 | May 12 | Oct 20 |
| 1966 | May 15 | Oct 10 | May 12 | Oct 10 |
"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.