Frost dates for Ross Dam, WA
At Ross Dam, the median last spring frost (32°F) is Apr 8 and the median first fall frost is Nov 10, for a typical growing season of 214 days. For a 90% chance that the last frost has passed, wait until Apr 30. Nearby ZIP codes are in USDA hardiness zones 6a to 8a.
- Apr 8Last spring frost (median)50% chance of 32°F after this date
- Apr 30Safer planting date10% chance of 32°F after this date
- Nov 10First fall frost (median)50% chance of 32°F by this date
- 214 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 | Apr 15 | Apr 30 | May 14 |
| 32°F | Mar 16 | Apr 8 | Apr 30 |
| 28°F | Feb 19 | Mar 11 | Mar 31 |
| 24°F | Jan 13 | Feb 22 | Mar 13 |
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 14 | Oct 26 | Nov 10 |
| 32°F | Oct 26 | Nov 10 | Nov 25 |
| 28°F | Nov 6 | Nov 25 | Dec 17 |
| 24°F | Nov 18 | Dec 9 | Jan 9 |
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 | 158 days | 178 days | 198 days |
| 32°F | 188 days | 214 days | 238 days |
| 28°F | 230 days | 257 days | 289 days |
| 24°F | 260 days | 295 days | 335 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 99% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 98283 | 7a | 0 to 5°F | 19 km |
| 98267 | 7a | 0 to 5°F | 40 km |
| 98833 | 6a | -10 to -5°F | 42 km |
| 98852 | 6b | -5 to 0°F | 50 km |
| 98237 | 8a | 10 to 15°F | 52 km |
| 98241 | 8a | 10 to 15°F | 58 km |
| 98244 | 8a | 10 to 15°F | 62 km |
| 98862 | 6b | -5 to 0°F | 64 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 USC00457185, at 48.7272, -121.0722, elevation 377 m (1,236 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 78.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Diablo Dam (5 km)
- Newhalem (14 km)
- Darrington 21 NNE (34 km)
- Upper Baker Dam (46 km)
- Stehekin 4 NW (49 km)
- Mazama (49 km)
- Concrete Ppl Fish Station (53 km)
- Holden Village (63 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.