Frost dates for Dillon U Of Montana Western, MT
At Dillon U Of Montana Western, the median last spring frost (32°F) is Jun 5 and the median first fall frost is Sep 13, for a typical growing season of 98 days. For a 90% chance that the last frost has passed, wait until Jun 23. Nearby ZIP codes are in USDA hardiness zones 4b to 5a.
- Jun 5Last spring frost (median)50% chance of 32°F after this date
- Jun 23Safer planting date10% chance of 32°F after this date
- Sep 13First fall frost (median)50% chance of 32°F by this date
- 98 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 18 | Jun 5 | Jun 23 |
| 28°F | May 3 | May 16 | Jun 3 |
| 24°F | Apr 20 | May 5 | 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 |
|---|---|---|---|
| 32°F | Aug 29 | Sep 13 | Sep 27 |
| 28°F | Sep 9 | Sep 25 | Oct 8 |
| 24°F | Sep 19 | Oct 4 | Oct 20 |
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 | 39 days | 65 days | 86 days |
| 32°F | 74 days | 98 days | 121 days |
| 28°F | 108 days | 130 days | 150 days |
| 24°F | 133 days | 153 days | 173 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59725 | 5a | -20 to -15°F | 21 km |
| 59732 | 4b | -25 to -20°F | 33 km |
| 59746 | 5a | -20 to -15°F | 38 km |
| 59754 | 5a | -20 to -15°F | 41 km |
| 59743 | 5a | -20 to -15°F | 45 km |
| 59710 | 5a | -20 to -15°F | 47 km |
| 59749 | 5a | -20 to -15°F | 52 km |
| 59755 | 5a | -20 to -15°F | 55 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 USC00242409, at 45.2089, -112.6389, elevation 1563 m (5,129 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 189.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Dillon Airport (9 km)
- Dillon 18 WSW (29 km)
- Glen 4 N (36 km)
- Twin Bridges (45 km)
- Alder 19s (45 km)
- Laurin 2ne (46 km)
- Alder 17 S (48 km)
- Virginia City (55 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.