Frost dates for Mystic Lake, MT
At Mystic Lake, the median last spring frost (32°F) is Jun 5 and the median first fall frost is Sep 14, for a typical growing season of 99 days. For a 90% chance that the last frost has passed, wait until Jun 21. Nearby ZIP codes are in USDA hardiness zone 5a.
- Jun 5Last spring frost (median)50% chance of 32°F after this date
- Jun 21Safer planting date10% chance of 32°F after this date
- Sep 14First fall frost (median)50% chance of 32°F by this date
- 99 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 22 | Jun 5 | Jun 21 |
| 28°F | May 7 | May 24 | Jun 11 |
| 24°F | Apr 26 | May 10 | May 31 |
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 31 | Sep 14 | Sep 28 |
| 28°F | Sep 7 | Sep 25 | Oct 10 |
| 24°F | Sep 15 | Oct 4 | Oct 22 |
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 | 47 days | 72 days | 94 days |
| 32°F | 76 days | 99 days | 120 days |
| 28°F | 98 days | 122 days | 143 days |
| 24°F | 118 days | 144 days | 167 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 |
|---|---|---|---|
| 59028 | 5a | -20 to -15°F | 7 km |
| 59071 | 5a | -20 to -15°F | 8 km |
| 59068 | 5a | -20 to -15°F | 22 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 USC00245961, at 45.2436, -109.7311, elevation 1995 m (6,544 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 178.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Nye #2 (22 km)
- Silver Gate (31 km)
- Cooke City 2 W (33 km)
- Red Lodge (38 km)
- Columbus (57 km)
- Joliet (62 km)
- Bridger 2 N (65 km)
- Big Timber (68 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.