Frost dates for Superior, MT
At Superior, the median last spring frost (32°F) is May 17 and the median first fall frost is Sep 23, for a typical growing season of 125 days. For a 90% chance that the last frost has passed, wait until Jun 8. Nearby ZIP codes are in USDA hardiness zone 6a.
- May 17Last spring frost (median)50% chance of 32°F after this date
- Jun 8Safer planting date10% chance of 32°F after this date
- Sep 23First fall frost (median)50% chance of 32°F by this date
- 125 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 20 | Jun 5 | Jul 3 |
| 32°F | May 1 | May 17 | Jun 8 |
| 28°F | Apr 16 | May 1 | May 19 |
| 24°F | Mar 25 | Apr 13 | May 4 |
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 9 | Sep 25 |
| 32°F | Sep 6 | Sep 23 | Oct 7 |
| 28°F | Sep 20 | Oct 6 | Oct 24 |
| 24°F | Oct 4 | Oct 23 | Nov 10 |
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 | 62 days | 92 days | 118 days |
| 32°F | 96 days | 125 days | 150 days |
| 28°F | 128 days | 157 days | 180 days |
| 24°F | 160 days | 191 days | 220 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 |
|---|---|---|---|
| 59872 | 6a | -10 to -5°F | 10 km |
| 59856 | 6a | -10 to -5°F | 24 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 USW00024159, at 47.1928, -114.8903, elevation 826 m (2,710 ft).
- Data quality: Representative (10+ years), 22 years of freeze data.
- Average days per year at or below 32°F: 161.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Saint Regis 1 NE (20 km)
- Alberton (38 km)
- Haugan 1 W (46 km)
- Thompson Falls Ph (57 km)
- Saint Ignatius (61 km)
- Missoula 6 NW WFO (67 km)
- Missoula Intl Airport (68 km)
- Skq Dam (73 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.