Frost dates for Augusta, MT
At Augusta, the median last spring frost (32°F) is May 19 and the median first fall frost is Sep 21, for a typical growing season of 125 days. For a 90% chance that the last frost has passed, wait until May 31. Nearby ZIP codes are in USDA hardiness zones 4a to 4b.
- May 19Last spring frost (median)50% chance of 32°F after this date
- May 31Safer planting date10% chance of 32°F after this date
- Sep 21First 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 3 | Jun 22 |
| 32°F | May 4 | May 19 | May 31 |
| 28°F | Apr 21 | May 6 | May 22 |
| 24°F | Apr 8 | Apr 27 | May 10 |
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 21 | Sep 8 | Sep 22 |
| 32°F | Sep 4 | Sep 21 | Oct 4 |
| 28°F | Sep 14 | Oct 1 | Oct 15 |
| 24°F | Sep 24 | Oct 9 | Oct 27 |
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 | 67 days | 96 days | 116 days |
| 32°F | 103 days | 125 days | 144 days |
| 28°F | 124 days | 145 days | 166 days |
| 24°F | 145 days | 167 days | 192 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59410 | 4b | -25 to -20°F | 19 km |
| 59436 | 4b | -25 to -20°F | 25 km |
| 59477 | 4b | -25 to -20°F | 32 km |
| 59422 | 4b | -25 to -20°F | 39 km |
| 59639 | 4b | -25 to -20°F | 43 km |
| 59443 | 4b | -25 to -20°F | 43 km |
| 59648 | 4b | -25 to -20°F | 47 km |
| 59483 | 4a | -30 to -25°F | 50 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 USC00240364, at 47.4925, -112.3969, elevation 1240 m (4,070 ft).
- Data quality: Representative (10+ years), 14 years of freeze data.
- Average days per year at or below 32°F: 176.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Gibson Dam (29 km)
- Fairfield (34 km)
- Rogers Pass 9 NNE (35 km)
- Choteau (40 km)
- Bynum 4 SSE (49 km)
- Sun River 4 S (50 km)
- Choteau 8ne (50 km)
- Blackleaf (58 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.