Frost dates for St. Marie, MT
At St. Marie, the median last spring frost (32°F) is May 13 and the median first fall frost is Sep 27, for a typical growing season of 134 days. For a 90% chance that the last frost has passed, wait until May 26. Nearby ZIP codes are in USDA hardiness zone 4a.
- May 13Last spring frost (median)50% chance of 32°F after this date
- May 26Safer planting date10% chance of 32°F after this date
- Sep 27First fall frost (median)50% chance of 32°F by this date
- 134 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 12 | May 24 | Jun 4 |
| 32°F | May 2 | May 13 | May 26 |
| 28°F | Apr 19 | May 3 | May 16 |
| 24°F | Apr 7 | Apr 22 | May 6 |
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 | Sep 5 | Sep 19 | Sep 30 |
| 32°F | Sep 13 | Sep 27 | Oct 9 |
| 28°F | Sep 22 | Oct 5 | Oct 21 |
| 24°F | Sep 29 | Oct 15 | Oct 30 |
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 | 99 days | 117 days | 133 days |
| 32°F | 116 days | 134 days | 151 days |
| 28°F | 136 days | 154 days | 174 days |
| 24°F | 153 days | 174 days | 195 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 |
|---|---|---|---|
| 59231 | 4a | -30 to -25°F | 2 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 USW00094010, at 48.4089, -106.5144, elevation 840 m (2,756 ft).
- Data quality: Representative (10+ years), 25 years of freeze data.
- Average days per year at or below 32°F: 179.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Glasgow Intl Airport (23 km)
- Glasgow #2 (26 km)
- Nashua #2 (33 km)
- Opheim 12 SSE (35 km)
- Fort Peck Power Plant (45 km)
- Hinsdale 4 SW (48 km)
- Saco 1 NNW (62 km)
- Opheim 10 N (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.