Frost dates for Chester, MT
At Chester, the median last spring frost (32°F) is May 24 and the median first fall frost is Sep 17, for a typical growing season of 115 days. For a 90% chance that the last frost has passed, wait until Jun 9. Nearby ZIP codes are in USDA hardiness zone 4a.
- May 24Last spring frost (median)50% chance of 32°F after this date
- Jun 9Safer planting date10% chance of 32°F after this date
- Sep 17First fall frost (median)50% chance of 32°F by this date
- 115 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 24 | Jun 9 | Jul 1 |
| 32°F | May 11 | May 24 | Jun 9 |
| 28°F | Apr 30 | May 11 | May 26 |
| 24°F | Apr 18 | May 2 | May 12 |
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 20 | Sep 5 | Sep 18 |
| 32°F | Sep 3 | Sep 17 | Sep 29 |
| 28°F | Sep 14 | Sep 26 | Oct 8 |
| 24°F | Sep 20 | Oct 3 | Oct 15 |
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 | 58 days | 85 days | 108 days |
| 32°F | 93 days | 115 days | 133 days |
| 28°F | 118 days | 137 days | 153 days |
| 24°F | 139 days | 154 days | 172 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 |
|---|---|---|---|
| 59522 | 4a | -30 to -25°F | 5 km |
| 59461 | 4a | -30 to -25°F | 18 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 USC00241692, at 48.5092, -110.9694, elevation 955 m (3,132 ft).
- Data quality: Representative (10+ years), 26 years of freeze data.
- Average days per year at or below 32°F: 198.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Joplin (16 km)
- Tiber Dam (24 km)
- Rudyard 19s (37 km)
- Dunkirk 19nne (44 km)
- Rudyard 21 N (47 km)
- Gildford (49 km)
- Brady 27 ENE (the Knees) (53 km)
- Goldbutte 7 N (61 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.