Frost dates for Simpson 6 N - Wildhorse, MT
At Simpson 6 N - Wildhorse, the median last spring frost (32°F) is May 26 and the median first fall frost is Sep 15, for a typical growing season of 110 days. For a 90% chance that the last frost has passed, wait until Jun 8. Nearby ZIP codes are in USDA hardiness zones 3b to 4a.
- May 26Last spring frost (median)50% chance of 32°F after this date
- Jun 8Safer planting date10% chance of 32°F after this date
- Sep 15First fall frost (median)50% chance of 32°F by this date
- 110 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 8 | Jul 3 |
| 32°F | May 12 | May 26 | Jun 8 |
| 28°F | May 1 | May 14 | May 28 |
| 24°F | Apr 18 | May 2 | May 17 |
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 18 | Sep 2 | Sep 16 |
| 32°F | Sep 1 | Sep 15 | Sep 25 |
| 28°F | Sep 9 | Sep 23 | Oct 4 |
| 24°F | Sep 18 | Oct 1 | Oct 14 |
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 | 56 days | 84 days | 105 days |
| 32°F | 91 days | 110 days | 128 days |
| 28°F | 113 days | 131 days | 149 days |
| 24°F | 131 days | 150 days | 170 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 |
|---|---|---|---|
| 59525 | 3b | -35 to -30°F | 40 km |
| 59528 | 4a | -30 to -25°F | 45 km |
| 59532 | 4a | -30 to -25°F | 46 km |
| 59501 | 3b | -35 to -30°F | 47 km |
| 59531 | 4a | -30 to -25°F | 49 km |
| 59540 | 3b | -35 to -30°F | 51 km |
| 59530 | 4a | -30 to -25°F | 56 km |
| 59545 | 4a | -30 to -25°F | 74 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 USC00247620, at 48.9981, -110.2158, elevation 858 m (2,815 ft).
- Data quality: Standard (24+ years of data), 26 years of freeze data.
- Average days per year at or below 32°F: 199.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Rudyard 21 N (32 km)
- Gildford (49 km)
- Havre City Co Airport (61 km)
- Fort Assiniboine (63 km)
- Joplin (64 km)
- Chester (78 km)
- Rudyard 19s (85 km)
- Chinook (86 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.