Frost dates for Bonneville Dam, OR
At Bonneville Dam, the median last spring frost (32°F) is Mar 14 and the median first fall frost is Nov 27, for a typical growing season of 257 days. For a 90% chance that the last frost has passed, wait until Apr 4. Nearby ZIP codes are in USDA hardiness zone 9a.
- Mar 14Last spring frost (median)50% chance of 32°F after this date
- Apr 4Safer planting date10% chance of 32°F after this date
- Nov 27First fall frost (median)50% chance of 32°F by this date
- 257 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 | Mar 23 | Apr 15 | May 5 |
| 32°F | Feb 19 | Mar 14 | Apr 4 |
| 28°F | Jan 4 | Feb 14 | Mar 10 |
| 24°F | Dec 17 | Jan 21 | Feb 26 |
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 | Oct 24 | Nov 10 | Nov 27 |
| 32°F | Nov 8 | Nov 27 | Dec 15 |
| 28°F | Nov 21 | Dec 14 | Jan 13 |
| 24°F | Dec 1 | Dec 30 | Feb 10 |
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 | 181 days | 207 days | 233 days |
| 32°F | 226 days | 257 days | 294 days |
| 28°F | 269 days | 306 days | 345 days |
| 24°F | 305 days | 342 days | 365 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 97% |
| 24°F | 71% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 98639 | 9a | 20 to 25°F | 1 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 USC00350897, at 45.6353, -121.9522, elevation 19 m (62 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 33.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Cascade Locks (8 km)
- Headworks Portland Wtr B (26 km)
- Parkdale 1 NNE (30 km)
- Hood River Exp. Station (34 km)
- Troutdale (35 km)
- Portland Troutdale Airport (37 km)
- Government Camp (41 km)
- Portland WFO (46 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.