Frost dates for Napa Co Airport, CA
At Napa Co Airport, the median last spring frost (32°F) is Mar 5 and the median first fall frost is Nov 21, for a typical growing season of 256 days. For a 90% chance that the last frost has passed, wait until Apr 16. Nearby ZIP codes are in USDA hardiness zone 9b.
- Mar 5Last spring frost (median)50% chance of 32°F after this date
- Apr 16Safer planting date10% chance of 32°F after this date
- Nov 21First fall frost (median)50% chance of 32°F by this date
- 256 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 | Mar 17 | Apr 17 | May 9 |
| 32°F | Jan 26 | Mar 5 | Apr 16 |
| 28°F | Dec 20 | Jan 23 | Feb 28 |
| 24°F | Dec 6 | Dec 31 | Feb 2 |
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 16 | Nov 4 | Nov 22 |
| 32°F | Nov 3 | Nov 21 | Dec 13 |
| 28°F | Nov 16 | Dec 5 | Jan 11 |
| 24°F | Nov 28 | Dec 17 | Jan 23 |
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 | 171 days | 199 days | 230 days |
| 32°F | 212 days | 256 days | 305 days |
| 28°F | 279 days | 323 days | 361 days |
| 24°F | 327 days | 361 days | 365 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 92% |
| 24°F | 52% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 94503 | 9b | 25 to 30°F | 6 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 USW00093227, at 38.2103, -122.2847, elevation 4 m (14 ft).
- Data quality: Representative (10+ years), 21 years of freeze data.
- Average days per year at or below 32°F: 34.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Napa State Hospital (8 km)
- Vallejo (15 km)
- Sonoma (18 km)
- Fairfield (20 km)
- Martinez Water Plant (27 km)
- Petaluma Airport (29 km)
- Concord Wastewater Plant (32 km)
- Concord Buchanan Field (32 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.