Port Costa, CA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Port Costa, a community in Contra Costa County, California.
Tonight
56°F
Mostly Clear
Mostly clear, with a low around 56. Southwest wind around 12 mph.
7-day forecast for Port Costa
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Tonight | 56°F | Mostly Clear | 12 mph SW | 0% |
| Saturday | 82°F | Sunny | 7 to 10 mph SW | 0% |
| Saturday Night | 57°F | Partly Cloudy | 12 mph SW | 0% |
| Sunday | 74°F | Partly Sunny | 12 mph SW | 1% |
| Sunday Night | 56°F | Mostly Cloudy | 13 mph SW | 1% |
| Monday | 75°F | Mostly Sunny | 13 mph SW | 0% |
| Monday Night | 56°F | Partly Cloudy | 8 to 13 mph SW | 0% |
| Tuesday | 79°F | Sunny | 7 to 10 mph SW | 0% |
| Tuesday Night | 57°F | Mostly Clear | 3 to 10 mph SW | 0% |
| Wednesday | 91°F | Sunny | 2 to 6 mph W | 0% |
| Wednesday Night | 60°F | Mostly Clear | 2 to 6 mph WSW | 0% |
| Thursday | 90°F | Sunny | 2 to 9 mph WSW | 0% |
| Thursday Night | 60°F | Partly Cloudy | 6 to 9 mph SW | 0% |
| Friday | 83°F | Mostly Sunny | 7 to 10 mph SW | 0% |
Forecast source: National Weather Service (api.weather.gov) for Port Costa (38.045, -122.185). Updated through the day.
Growing snapshot for Port Costa
Last spring frost
Jan 17
First fall frost
Dec 27
Growing season
346 days
Hardiness zone
9b
More local growing data for Port Costa: nearby ZIP 94569 weather · frost dates · planting calendar · California frost dates
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Climate data from the nearest NOAA station, Vallejo, Ca (3.9 mi from Port Costa). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.