Frost dates for Flatwillow 4 ENE, MT
At Flatwillow 4 ENE, the median last spring frost (32°F) is May 16 and the median first fall frost is Sep 28, for a typical growing season of 132 days. For a 90% chance that the last frost has passed, wait until May 31. Nearby ZIP codes are in USDA hardiness zone 4b.
- May 16Last spring frost (median)50% chance of 32°F after this date
- May 31Safer planting date10% chance of 32°F after this date
- Sep 28First fall frost (median)50% chance of 32°F by this date
- 132 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 15 | May 29 | Jun 14 |
| 32°F | May 3 | May 16 | May 31 |
| 28°F | Apr 21 | May 3 | May 17 |
| 24°F | Apr 7 | Apr 22 | May 6 |
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 | Sep 4 | Sep 17 | Sep 30 |
| 32°F | Sep 15 | Sep 28 | Oct 10 |
| 28°F | Sep 24 | Oct 5 | Oct 20 |
| 24°F | Sep 30 | Oct 16 | Nov 2 |
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 | 91 days | 110 days | 129 days |
| 32°F | 112 days | 132 days | 151 days |
| 28°F | 133 days | 153 days | 173 days |
| 24°F | 154 days | 176 days | 199 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 |
|---|---|---|---|
| 59032 | 4b | -25 to -20°F | 34 km |
| 59072 | 4b | -25 to -20°F | 36 km |
| 59087 | 4b | -25 to -20°F | 37 km |
| 59059 | 4b | -25 to -20°F | 41 km |
| 59054 | 4b | -25 to -20°F | 49 km |
| 59058 | 4b | -25 to -20°F | 50 km |
| 59441 | 4b | -25 to -20°F | 53 km |
| 59046 | 4b | -25 to -20°F | 68 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 USC00243013, at 46.8217, -108.3725, elevation 1003 m (3,292 ft).
- Data quality: Standard (24+ years of data), 26 years of freeze data.
- Average days per year at or below 32°F: 172.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Grass Range (40 km)
- Roundup (44 km)
- Melstone (45 km)
- Mosby 4 ENE (47 km)
- Valentine (58 km)
- Roundup 15 SW (62 km)
- Lewistown 11ese (68 km)
- Pompeys Pillar 15n (75 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.