Frost dates for Dillon Airport, MT
At Dillon Airport, the median last spring frost (32°F) is Jun 2 and the median first fall frost is Sep 13, for a typical growing season of 101 days. For a 90% chance that the last frost has passed, wait until Jun 21. Nearby ZIP codes are in USDA hardiness zones 4b to 5a.
- Jun 2Last spring frost (median)50% chance of 32°F after this date
- Jun 21Safer planting date10% chance of 32°F after this date
- Sep 13First fall frost (median)50% chance of 32°F by this date
- 101 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 17 | Jun 2 | Jun 21 |
| 28°F | May 1 | May 14 | Jun 1 |
| 24°F | Apr 18 | May 2 | May 14 |
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 30 | Sep 13 | Sep 28 |
| 28°F | Sep 11 | Sep 27 | Oct 10 |
| 24°F | Sep 22 | 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 | 44 days | 68 days | 89 days |
| 32°F | 77 days | 101 days | 122 days |
| 28°F | 109 days | 132 days | 152 days |
| 24°F | 136 days | 156 days | 176 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 |
|---|---|---|---|
| 59732 | 4b | -25 to -20°F | 29 km |
| 59725 | 5a | -20 to -15°F | 30 km |
| 59754 | 5a | -20 to -15°F | 33 km |
| 59743 | 5a | -20 to -15°F | 42 km |
| 59746 | 5a | -20 to -15°F | 42 km |
| 59710 | 5a | -20 to -15°F | 43 km |
| 59749 | 5a | -20 to -15°F | 44 km |
| 59755 | 5a | -20 to -15°F | 48 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 USW00024138, at 45.2575, -112.5545, elevation 1585 m (5,200 ft).
- Data quality: Standard (24+ years of data), 25 years of freeze data.
- Average days per year at or below 32°F: 193.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Dillon U Of Montana Western (9 km)
- Glen 4 N (32 km)
- Twin Bridges (37 km)
- Dillon 18 WSW (37 km)
- Laurin 2ne (38 km)
- Alder 19s (41 km)
- Alder 17 S (44 km)
- Virginia City (48 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.