Frost dates for Bismarck WFO, ND
At Bismarck WFO, the median last spring frost (32°F) is May 14 and the median first fall frost is Sep 30, for a typical growing season of 138 days. For a 90% chance that the last frost has passed, wait until May 27. Nearby ZIP codes are in USDA hardiness zone 4a.
- May 14Last spring frost (median)50% chance of 32°F after this date
- May 27Safer planting date10% chance of 32°F after this date
- Sep 30First fall frost (median)50% chance of 32°F by this date
- 138 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 12 | May 23 | Jun 5 |
| 32°F | May 1 | May 14 | May 27 |
| 28°F | Apr 17 | May 3 | May 18 |
| 24°F | Apr 7 | Apr 23 | 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 8 | Sep 21 | Oct 3 |
| 32°F | Sep 18 | Sep 30 | Oct 13 |
| 28°F | Sep 25 | Oct 8 | Oct 21 |
| 24°F | Oct 4 | Oct 18 | Oct 30 |
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 | 100 days | 119 days | 138 days |
| 32°F | 119 days | 138 days | 156 days |
| 28°F | 136 days | 156 days | 176 days |
| 24°F | 155 days | 177 days | 195 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 |
|---|---|---|---|
| 58501 | 4a | -30 to -25°F | 7 km |
| 58504 | 4a | -30 to -25°F | 7 km |
| 58558 | 4a | -30 to -25°F | 19 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 USC00320818, at 46.7717, -100.7592, elevation 503 m (1,651 ft).
- Data quality: Estimated from nearby stations (2+ years), 9 years of freeze data.
- Average days per year at or below 32°F: 184.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Bismarck (0 km)
- Bismarck 2.4 NNW (7 km)
- Mandan Exp. Station (12 km)
- Moffit 3 SE (42 km)
- Hazelton 4nw (42 km)
- Wilton (43 km)
- Breien (46 km)
- Center 4se (47 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.