Frost dates for Sun River 4 S, MT
At Sun River 4 S, the median last spring frost (32°F) is Jun 2 and the median first fall frost is Sep 10, for a typical growing season of 96 days. For a 90% chance that the last frost has passed, wait until Jun 21. Nearby ZIP codes are in USDA hardiness zones 4a to 4b.
- Jun 2Last spring frost (median)50% chance of 32°F after this date
- Jun 21Safer planting date10% chance of 32°F after this date
- Sep 10First fall frost (median)50% chance of 32°F by this date
- 96 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 18 | Jun 2 | Jun 21 |
| 28°F | May 5 | May 18 | May 31 |
| 24°F | Apr 22 | May 6 | May 18 |
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 25 | Sep 10 | Sep 25 |
| 28°F | Sep 6 | Sep 22 | Oct 7 |
| 24°F | Sep 17 | Oct 2 | Oct 18 |
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 | 37 days | 62 days | 85 days |
| 32°F | 71 days | 96 days | 119 days |
| 28°F | 104 days | 127 days | 146 days |
| 24°F | 130 days | 148 days | 168 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 |
|---|---|---|---|
| 59483 | 4a | -30 to -25°F | 1 km |
| 59443 | 4b | -25 to -20°F | 12 km |
| 59485 | 4a | -30 to -25°F | 14 km |
| 59487 | 4a | -30 to -25°F | 14 km |
| 59477 | 4b | -25 to -20°F | 18 km |
| 59468 | 4b | -25 to -20°F | 29 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 USC00248021, at 47.4772, -111.7375, elevation 1097 m (3,600 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 170.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Fairfield (24 km)
- Great Falls WFO (27 km)
- Great Falls Intl Airport (27 km)
- Cascade 5 S (29 km)
- Great Falls 16st (34 km)
- Choteau 8ne (48 km)
- Augusta (50 km)
- Choteau (51 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.