Frost dates for Angwin Pacific Union College, CA
At Angwin Pacific Union College, the median last spring frost (32°F) is Apr 7 and the median first fall frost is Dec 5, for a typical growing season of 245 days. For a 90% chance that the last frost has passed, wait until Apr 30. Nearby ZIP codes are in USDA hardiness zones 9a to 9b.
- Apr 7Last spring frost (median)50% chance of 32°F after this date
- Apr 30Safer planting date10% chance of 32°F after this date
- Dec 5First fall frost (median)50% chance of 32°F by this date
- 245 daysGrowing season (median)between 32°F freezes
USDA hardiness zone 9b (25 to 30°F) · see all zone 9b frost dates
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 6 | Apr 30 | May 25 |
| 32°F | Feb 23 | Apr 7 | Apr 30 |
| 28°F | Dec 23 | Feb 18 | Apr 9 |
| 24°F | Dec 5 | Jan 1 | 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 22 | Nov 15 | Dec 5 |
| 32°F | Nov 14 | Dec 5 | Jan 1 |
| 28°F | Nov 29 | Dec 30 | Mar 4 |
| 24°F | Dec 4 | Dec 31 | Feb 24 |
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 | 163 days | 195 days | 225 days |
| 32°F | 209 days | 245 days | 293 days |
| 28°F | 259 days | 321 days | 365 days |
| 24°F | 347 days | 365 days | 365 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 83% |
| 24°F | 20% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 94508 | 9b | 25 to 30°F | 1 km |
| 94574 | 9b | 25 to 30°F | 4 km |
| 94576 | 9b | 25 to 30°F | 4 km |
| 94567 | 9a | 20 to 25°F | 11 km |
| 95606 | 9a | 20 to 25°F | 30 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 USC00040212, at 38.5731, -122.4406, elevation 523 m (1,715 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 15.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Saint Helena (8 km)
- Calistoga (14 km)
- Santa Rosa (27 km)
- Markley Cove (29 km)
- Sonoma (30 km)
- Santa Rosa Sonoma Co Airport (33 km)
- Napa State Hospital (36 km)
- Healdsburg (38 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.