Frost dates for Boundary Dam, WA
At Boundary Dam, the median last spring frost (32°F) is May 4 and the median first fall frost is Oct 4, for a typical growing season of 153 days. For a 90% chance that the last frost has passed, wait until May 18. Nearby ZIP codes are in USDA hardiness zone 6a.
- May 4Last spring frost (median)50% chance of 32°F after this date
- May 18Safer planting date10% chance of 32°F after this date
- Oct 4First fall frost (median)50% chance of 32°F by this date
- 153 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 6 | May 19 | Jun 2 |
| 32°F | Apr 20 | May 4 | May 18 |
| 28°F | Apr 1 | Apr 17 | May 2 |
| 24°F | Mar 14 | Mar 31 | Apr 16 |
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 21 | Oct 5 |
| 32°F | Sep 21 | Oct 4 | Oct 20 |
| 28°F | Oct 1 | Oct 19 | Nov 4 |
| 24°F | Oct 15 | Nov 2 | Nov 22 |
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 | 103 days | 123 days | 145 days |
| 32°F | 132 days | 153 days | 173 days |
| 28°F | 161 days | 184 days | 208 days |
| 24°F | 190 days | 216 days | 240 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 |
|---|---|---|---|
| 99153 | 6a | -10 to -5°F | 17 km |
| 99152 | 6a | -10 to -5°F | 18 km |
| 99139 | 6a | -10 to -5°F | 32 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 USC00450844, at 48.9947, -117.3544, elevation 560 m (1,837 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 174.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Northport (36 km)
- Colville (64 km)
- Chewelah (85 km)
- Newport (93 km)
- Republic (108 km)
- Deer Park Airport (114 km)
- Tonasket 11ne (141 km)
- Spokane Felts Field (146 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.