Frost dates for Busby, MT
At Busby, the median last spring frost (32°F) is May 23 and the median first fall frost is Sep 15, for a typical growing season of 113 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 23Last spring frost (median)50% chance of 32°F after this date
- Jun 7Safer planting date10% chance of 32°F after this date
- Sep 15First fall frost (median)50% chance of 32°F by this date
- 113 daysGrowing season (median)between 32°F freezes
USDA hardiness zone 5a (-20 to -15°F) · see all zone 5a frost dates
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 24 | Jun 8 | Jul 2 |
| 32°F | May 12 | May 23 | Jun 7 |
| 28°F | Apr 30 | May 11 | May 24 |
| 24°F | Apr 14 | Apr 29 | May 11 |
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 20 | Sep 4 | Sep 18 |
| 32°F | Sep 1 | Sep 15 | Oct 1 |
| 28°F | Sep 11 | Sep 27 | Oct 11 |
| 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 | 60 days | 86 days | 107 days |
| 32°F | 93 days | 113 days | 131 days |
| 28°F | 117 days | 136 days | 155 days |
| 24°F | 139 days | 158 days | 178 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 |
|---|---|---|---|
| 59016 | 5a | -20 to -15°F | 9 km |
| 59043 | 5a | -20 to -15°F | 22 km |
| 59022 | 4b | -25 to -20°F | 24 km |
| 59012 | 4b | -25 to -20°F | 35 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 USC00241297, at 45.5397, -106.9597, elevation 1046 m (3,430 ft).
- Data quality: Standard (24+ years of data), 30 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
- Hysham 25 SSE (46 km)
- Colstrip (47 km)
- Hardin (55 km)
- Wyola 1 SW (58 km)
- Brandenberg (64 km)
- Yellowtail Dam (80 km)
- Forsyth (84 km)
- Sonnette 7 SW (85 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.