Frost dates for St. Mary 1 SSW, MT
At St. Mary 1 SSW, the median last spring frost (32°F) is Jun 3 and the median first fall frost is Sep 8, for a typical growing season of 94 days. For a 90% chance that the last frost has passed, wait until Jun 23. Nearby ZIP codes are in USDA hardiness zone 4b.
- Jun 3Last spring frost (median)50% chance of 32°F after this date
- Jun 23Safer planting date10% chance of 32°F after this date
- Sep 8First fall frost (median)50% chance of 32°F by this date
- 94 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 19 | Jun 3 | Jun 23 |
| 28°F | May 2 | May 14 | May 28 |
| 24°F | Apr 14 | May 1 | May 15 |
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 22 | Sep 8 | Sep 26 |
| 28°F | Sep 7 | Sep 25 | Oct 9 |
| 24°F | Sep 22 | Oct 5 | Oct 24 |
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 | 30 days | 51 days | 75 days |
| 32°F | 68 days | 94 days | 117 days |
| 28°F | 111 days | 131 days | 152 days |
| 24°F | 137 days | 158 days | 182 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 |
|---|---|---|---|
| 59434 | 4b | -25 to -20°F | 7 km |
| 59411 | 4b | -25 to -20°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 USW00004130, at 48.7411, -113.4331, elevation 1388 m (4,555 ft).
- Data quality: Representative (10+ years), 16 years of freeze data.
- Average days per year at or below 32°F: 181.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- St. Mary (0 km)
- E Glacier (36 km)
- W Glacier (49 km)
- Del Bonita (55 km)
- Hungry Horse Dam (62 km)
- Polebridge (62 km)
- Whitefish (78 km)
- Kalispell Glacier Airport (78 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.