Frost dates for Heart Butte Dam, ND
At Heart Butte Dam, the median last spring frost (32°F) is May 14 and the median first fall frost is Sep 29, for a typical growing season of 136 days. For a 90% chance that the last frost has passed, wait until May 28. Nearby ZIP codes are in USDA hardiness zone 4a.
- May 14Last spring frost (median)50% chance of 32°F after this date
- May 28Safer planting date10% chance of 32°F after this date
- Sep 29First fall frost (median)50% chance of 32°F by this date
- 136 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 13 | May 24 | Jun 5 |
| 32°F | May 3 | May 14 | May 28 |
| 28°F | Apr 21 | May 5 | May 18 |
| 24°F | Apr 11 | Apr 26 | May 9 |
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 20 | Oct 1 |
| 32°F | Sep 16 | Sep 29 | Oct 10 |
| 28°F | Sep 23 | Oct 6 | Oct 18 |
| 24°F | Oct 1 | Oct 14 | 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 | 98 days | 117 days | 135 days |
| 32°F | 118 days | 136 days | 153 days |
| 28°F | 134 days | 153 days | 173 days |
| 24°F | 152 days | 172 days | 191 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 |
|---|---|---|---|
| 58520 | 4a | -30 to -25°F | 20 km |
| 58533 | 4a | -30 to -25°F | 22 km |
| 58631 | 4a | -30 to -25°F | 23 km |
| 58562 | 4a | -30 to -25°F | 30 km |
| 58529 | 4a | -30 to -25°F | 36 km |
| 58638 | 4a | -30 to -25°F | 40 km |
| 58646 | 4a | -30 to -25°F | 43 km |
| 58563 | 4a | -30 to -25°F | 44 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 USC00324091, at 46.5917, -101.8075, elevation 650 m (2,134 ft).
- Data quality: Standard (24+ years of data), 30 years of freeze data.
- Average days per year at or below 32°F: 189.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Carson (26 km)
- Almont (27 km)
- Hebron (39 km)
- New Salem 5nw (41 km)
- Mott (46 km)
- Pretty Rock (46 km)
- Flasher (49 km)
- Richardton Abbey (51 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.