Frost dates for Shelby, MT
At Shelby, the median last spring frost (32°F) is May 23 and the median first fall frost is Sep 16, for a typical growing season of 115 days. For a 90% chance that the last frost has passed, wait until Jun 6. Nearby ZIP codes are in USDA hardiness zone 4a.
- May 23Last spring frost (median)50% chance of 32°F after this date
- Jun 6Safer planting date10% chance of 32°F after this date
- Sep 16First fall frost (median)50% chance of 32°F by this date
- 115 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 |
|---|---|---|---|
| 36°F | May 23 | Jun 5 | Jun 21 |
| 32°F | May 11 | May 23 | Jun 6 |
| 28°F | Apr 30 | May 10 | May 22 |
| 24°F | Apr 14 | Apr 29 | May 12 |
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 23 | Sep 5 | Sep 18 |
| 32°F | Sep 3 | Sep 16 | Sep 28 |
| 28°F | Sep 13 | Sep 26 | Oct 7 |
| 24°F | Sep 21 | Oct 5 | Oct 18 |
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 | 70 days | 90 days | 107 days |
| 32°F | 97 days | 115 days | 132 days |
| 28°F | 121 days | 138 days | 155 days |
| 24°F | 140 days | 159 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 |
|---|---|---|---|
| 59474 | 4a | -30 to -25°F | 12 km |
| 59435 | 4a | -30 to -25°F | 15 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 USC00247500, at 48.5133, -111.8550, elevation 1014 m (3,325 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 190.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Dunkirk 19nne (36 km)
- Valier (37 km)
- Conrad (38 km)
- Cut Bank Muni Airport (40 km)
- Sunburst 8 E (43 km)
- Sweetgrass (54 km)
- Tiber Dam (61 km)
- Goldbutte 7 N (61 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.