Frost dates for Alberton, MT
At Alberton, the median last spring frost (32°F) is May 18 and the median first fall frost is Sep 25, for a typical growing season of 126 days. For a 90% chance that the last frost has passed, wait until Jun 6. Nearby ZIP codes are in USDA hardiness zone 5b.
- May 18Last spring frost (median)50% chance of 32°F after this date
- Jun 6Safer planting date10% chance of 32°F after this date
- Sep 25First fall frost (median)50% chance of 32°F by this date
- 126 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 11 | Jul 2 |
| 32°F | May 5 | May 18 | Jun 6 |
| 28°F | Apr 20 | May 3 | May 15 |
| 24°F | Mar 28 | Apr 17 | May 2 |
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 28 | Sep 9 | Sep 26 |
| 32°F | Sep 7 | Sep 25 | Oct 6 |
| 28°F | Sep 23 | Oct 5 | Oct 21 |
| 24°F | Oct 3 | Oct 18 | Nov 3 |
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 | 65 days | 92 days | 114 days |
| 32°F | 104 days | 126 days | 146 days |
| 28°F | 134 days | 153 days | 174 days |
| 24°F | 159 days | 184 days | 209 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 |
|---|---|---|---|
| 59820 | 5b | -15 to -10°F | 15 km |
| 59846 | 5b | -15 to -10°F | 17 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 USC00240075, at 47.0036, -114.4781, elevation 933 m (3,060 ft).
- Data quality: Representative (10+ years), 18 years of freeze data.
- Average days per year at or below 32°F: 183.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Missoula 6 NW WFO (31 km)
- Missoula Intl Airport (31 km)
- Superior (38 km)
- Missoula 2 NE (40 km)
- Saint Ignatius (45 km)
- Saint Regis 1 NE (57 km)
- Stevensville (62 km)
- Potomac (71 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.