Frost dates for Del Bonita, MT
At Del Bonita, the median last spring frost (32°F) is May 28 and the median first fall frost is Sep 16, for a typical growing season of 110 days. For a 90% chance that the last frost has passed, wait until Jun 12. Nearby ZIP codes are in USDA hardiness zones 4a to 4b.
- May 28Last spring frost (median)50% chance of 32°F after this date
- Jun 12Safer planting date10% chance of 32°F after this date
- Sep 16First fall frost (median)50% chance of 32°F by this date
- 110 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 12 | May 28 | Jun 12 |
| 28°F | Apr 29 | May 13 | May 28 |
| 24°F | Apr 15 | May 1 | May 16 |
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 28 | Sep 16 | Sep 28 |
| 28°F | Sep 13 | Sep 27 | Oct 10 |
| 24°F | Sep 26 | Oct 7 | Oct 22 |
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 | 50 days | 78 days | 100 days |
| 32°F | 83 days | 110 days | 132 days |
| 28°F | 116 days | 137 days | 157 days |
| 24°F | 139 days | 158 days | 179 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 |
|---|---|---|---|
| 59427 | 4a | -30 to -25°F | 30 km |
| 59411 | 4b | -25 to -20°F | 46 km |
| 59417 | 4a | -30 to -25°F | 52 km |
| 59434 | 4b | -25 to -20°F | 62 km |
| 59454 | 4a | -30 to -25°F | 64 km |
| 59482 | 4a | -30 to -25°F | 70 km |
| 59435 | 4a | -30 to -25°F | 72 km |
| 59486 | 4b | -25 to -20°F | 79 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 USC00242301, at 48.9983, -112.7886, elevation 1322 m (4,337 ft).
- Data quality: Representative (10+ years), 19 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
- Cut Bank Muni Airport (53 km)
- St. Mary (55 km)
- St. Mary 1 SSW (55 km)
- Sweetgrass (60 km)
- E Glacier (69 km)
- Sunburst 8 E (78 km)
- Valier (86 km)
- Shelby (87 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.