Frost history / Roundup 15 Sw, MT
Roundup 15 Sw, MT: frost dates by year
Last spring and first fall frost at NOAA station USC00247220, 2005 to 2025, measured from daily minimum temperatures.
Elevation 3,386 ft, 46.325, -108.740. Download the data (JSON), NOAA daily records
Summary at 32°F
| Last spring frost | First fall frost | |
|---|---|---|
| Median | May 20 | Sep 22 |
| Earliest | Apr 27 (2018) | Aug 23 (2015) |
| Latest | Jun 11 (2008) | Oct 13 (2010) |
| Trend | 6.3 days earlier per decade | 8.2 days later per decade |
| Years with data | 18 | 18 |
At 28°F (hard freeze) the median last spring date is May 7 and the median first fall date is Oct 3.
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 22 | no data | May 2 | no data |
| 2024 | May 24 | Oct 1 | May 5 | Oct 13 |
| 2023 | May 10 | Oct 6 | Apr 29 | Oct 7 |
| 2022 | May 25 | Oct 7 | May 22 | Oct 17 |
| 2021 | no data | Sep 17 | no data | Sep 17 |
| 2020 | May 14 | Sep 9 | Apr 26 | Sep 9 |
| 2019 | May 19 | Sep 29 | May 10 | Sep 30 |
| 2018 | Apr 27 | Sep 26 | Apr 17 | Sep 26 |
| 2017 | May 20 | Sep 17 | May 19 | Sep 25 |
| 2016 | May 17 | Oct 6 | May 14 | Oct 6 |
| 2015 | May 21 | Aug 23 | May 20 | Oct 15 |
| 2014 | Jun 7 | Sep 12 | May 8 | Sep 12 |
| 2013 | May 12 | Sep 22 | May 3 | Sep 22 |
| 2012 | May 29 | no data | May 12 | no data |
| 2011 | May 18 | Sep 4 | May 6 | Sep 21 |
| 2010 | no data | Oct 13 | no data | Oct 16 |
| 2009 | Jun 8 | Sep 22 | May 21 | Oct 6 |
| 2008 | Jun 11 | no data | May 4 | no data |
| 2007 | May 25 | Sep 10 | Apr 23 | Sep 14 |
| 2006 | May 14 | Sep 2 | May 11 | Oct 13 |
| 2005 | no data | Sep 22 | no data | Oct 6 |
"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.