Frost dates for Sonnette 7 SW, MT
At Sonnette 7 SW, the median last spring frost (32°F) is May 25 and the median first fall frost is Sep 19, for a typical growing season of 115 days. For a 90% chance that the last frost has passed, wait until Jun 7. Nearby ZIP codes are in USDA hardiness zones 4b to 5a.
- May 25Last spring frost (median)50% chance of 32°F after this date
- Jun 7Safer planting date10% chance of 32°F after this date
- Sep 19First fall frost (median)50% chance of 32°F by this date
- 115 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 23 | Jun 7 | Jun 27 |
| 32°F | May 12 | May 25 | Jun 7 |
| 28°F | May 2 | May 14 | May 27 |
| 24°F | Apr 19 | May 2 | May 18 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Aug 18 | Sep 6 | Sep 20 |
| 32°F | Sep 1 | Sep 19 | Oct 1 |
| 28°F | Sep 14 | Sep 29 | Oct 12 |
| 24°F | Sep 23 | Oct 6 | Oct 21 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 64 days | 89 days | 108 days |
| 32°F | 94 days | 115 days | 133 days |
| 28°F | 115 days | 136 days | 153 days |
| 24°F | 136 days | 156 days | 177 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59003 | 4b | -25 to -20°F | 29 km |
| 59062 | 5a | -20 to -15°F | 31 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00247740, at 45.3242, -105.9136, elevation 1193 m (3,914 ft).
- Data quality: Standard (24+ years of data), 26 years of freeze data.
- Average days per year at or below 32°F: 198.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Moorhead 9 NE (21 km)
- Broadus (42 km)
- Biddle 8 SW (46 km)
- Brandenberg (60 km)
- Colstrip (85 km)
- Busby (85 km)
- Powderville 8 NNE (90 km)
- Ridgeway 1 S (116 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.