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.
This Afternoon
60°F
Light Rain
Rain. Mostly cloudy. High near 60, with temperatures falling to around 55 in the afternoon. South wind around 7 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch possible.
7-day forecast for Port Costa
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 60°F | Light Rain | 7 mph S | 85% |
| Tonight | 48°F | Light Rain Likely then Mostly Cloudy | 9 mph E | 55% |
| Wednesday | 65°F | Sunny | 5 to 8 mph NW | 1% |
| Wednesday Night | 48°F | Partly Cloudy | 5 to 8 mph WNW | 0% |
| Thursday | 69°F | Sunny | 5 mph WNW | 0% |
| Thursday Night | 49°F | Mostly Clear | 5 mph WSW | 0% |
| Friday | 71°F | Sunny | 1 to 5 mph N | 0% |
| Friday Night | 49°F | Clear | 2 mph W | 0% |
| Saturday | 72°F | Sunny | 1 to 8 mph NE | 0% |
| Saturday Night | 50°F | Mostly Clear | 2 mph WNW | 0% |
| Sunday | 71°F | Mostly Sunny | 1 to 5 mph WNW | 0% |
| Sunday Night | 51°F | Partly Cloudy | 2 mph W | 0% |
| Monday | 69°F | Partly Sunny | 5 mph WSW | 1% |
| Monday Night | 51°F | Partly Cloudy | 3 mph WSW | 2% |
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 Nov 4, 2026.