Frost dates for Copco #1 Dam, CA
At Copco #1 Dam, the median last spring frost (32°F) is May 4 and the median first fall frost is Oct 21, for a typical growing season of 168 days. For a 90% chance that the last frost has passed, wait until May 31. Nearby ZIP codes are in USDA hardiness zones 6b to 8a.
- May 4Last spring frost (median)50% chance of 32°F after this date
- May 31Safer planting date10% chance of 32°F after this date
- Oct 21First fall frost (median)50% chance of 32°F by this date
- 168 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 2 | May 23 | Jun 10 |
| 32°F | Apr 15 | May 4 | May 31 |
| 28°F | Mar 21 | Apr 16 | May 14 |
| 24°F | Feb 16 | Mar 20 | Apr 27 |
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 30 | Oct 9 | Oct 22 |
| 32°F | Oct 10 | Oct 21 | Nov 4 |
| 28°F | Oct 20 | Nov 4 | Nov 21 |
| 24°F | Nov 3 | Nov 21 | Dec 7 |
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 | 117 days | 138 days | 162 days |
| 32°F | 139 days | 168 days | 194 days |
| 28°F | 165 days | 198 days | 231 days |
| 24°F | 203 days | 241 days | 281 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 |
|---|---|---|---|
| 97627 | 6b | -5 to 0°F | 24 km |
| 96064 | 7b | 5 to 10°F | 25 km |
| 97520 | 8a | 10 to 15°F | 26 km |
| 96044 | 8a | 10 to 15°F | 28 km |
| 96023 | 6b | -5 to 0°F | 31 km |
| 96097 | 8a | 10 to 15°F | 36 km |
| 96038 | 8a | 10 to 15°F | 45 km |
| 96058 | 6b | -5 to 0°F | 45 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 USC00041990, at 41.9797, -122.3378, elevation 824 m (2,703 ft).
- Data quality: Representative (10+ years), 10 years of freeze data.
- Average days per year at or below 32°F: 119.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Montague Siskiyou Co Airport (25 km)
- Yreka (40 km)
- Tulelake (71 km)
- Mount Shasta (72 km)
- Mount Shasta (73 km)
- Lava Beds Nat Mon (76 km)
- Callahan (82 km)
- McCloud (83 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.