Frost dates for Western Ag Rsch Center, MT
At Western Ag Rsch Center, the median last spring frost (32°F) is May 23 and the median first fall frost is Sep 21, for a typical growing season of 118 days. For a 90% chance that the last frost has passed, wait until Jun 10. Nearby ZIP codes are in USDA hardiness zone 5b.
- May 23Last spring frost (median)50% chance of 32°F after this date
- Jun 10Safer planting date10% chance of 32°F after this date
- Sep 21First fall frost (median)50% chance of 32°F by this date
- 118 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 27 | Jun 12 | Jul 1 |
| 32°F | May 8 | May 23 | Jun 10 |
| 28°F | Apr 22 | May 5 | May 19 |
| 24°F | Apr 3 | Apr 23 | May 8 |
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 24 | Sep 8 | Sep 22 |
| 32°F | Sep 5 | Sep 21 | Oct 4 |
| 28°F | Sep 16 | Oct 2 | Oct 16 |
| 24°F | Sep 28 | Oct 14 | Oct 29 |
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 | 59 days | 84 days | 105 days |
| 32°F | 94 days | 118 days | 140 days |
| 28°F | 126 days | 148 days | 166 days |
| 24°F | 150 days | 173 days | 196 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 |
|---|---|---|---|
| 59828 | 5b | -15 to -10°F | 10 km |
| 59841 | 5b | -15 to -10°F | 11 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 USC00248783, at 46.3283, -114.0847, elevation 1100 m (3,608 ft).
- Data quality: Representative (10+ years), 21 years of freeze data.
- Average days per year at or below 32°F: 165.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Hamilton (11 km)
- Stevensville (21 km)
- Darby (34 km)
- Sula 14 NE (53 km)
- Sula 3 ENE (55 km)
- Phillipsburg Ranger Station (60 km)
- Missoula 2 NE (64 km)
- Missoula Intl Airport (66 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.