Frost dates for Twin Bridges, MT
At Twin Bridges, the median last spring frost (32°F) is Jun 8 and the median first fall frost is Sep 2, for a typical growing season of 82 days. For a 90% chance that the last frost has passed, wait until Jul 1. Nearby ZIP codes are in USDA hardiness zone 5a.
- Jun 8Last spring frost (median)50% chance of 32°F after this date
- Jul 1Safer planting date10% chance of 32°F after this date
- Sep 2First fall frost (median)50% chance of 32°F by this date
- 82 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 |
|---|---|---|---|
| 32°F | May 22 | Jun 8 | Jul 1 |
| 28°F | May 7 | May 20 | Jun 6 |
| 24°F | Apr 25 | May 7 | May 21 |
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 |
|---|---|---|---|
| 32°F | Aug 16 | Sep 2 | Sep 15 |
| 28°F | Aug 31 | Sep 15 | Oct 1 |
| 24°F | Sep 12 | Sep 29 | Oct 12 |
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 | 27 days | 46 days | 71 days |
| 32°F | 56 days | 82 days | 105 days |
| 28°F | 92 days | 116 days | 136 days |
| 24°F | 122 days | 142 days | 160 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 |
|---|---|---|---|
| 59754 | 5a | -20 to -15°F | 4 km |
| 59751 | 5a | -20 to -15°F | 16 km |
| 59747 | 5a | -20 to -15°F | 33 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 USC00248430, at 45.5472, -112.3261, elevation 1410 m (4,625 ft).
- Data quality: Standard (24+ years of data), 30 years of freeze data.
- Average days per year at or below 32°F: 206.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Laurin 2ne (27 km)
- Glen 4 N (29 km)
- Dillon Airport (37 km)
- Divide (40 km)
- Virginia City (41 km)
- Dillon U Of Montana Western (45 km)
- Butte Bert Mooney Airport (48 km)
- Ennis (53 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.