Port Costa, CA Weather & Growing Conditions
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
| 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). Updated through the day.
Growing snapshot for Port Costa, CA
Last spring frost
Jan 17
First fall frost
Dec 27
Growing season
346 days
Hardiness zone
9b
Explore more for Port Costa, CA: full frost dates · planting calendar · California frost dates
Climate data from the nearest NOAA station, Vallejo, Ca (3.9 mi). Frost dates are 1991–2020 averages, not a forecast. Page updated Nov 4, 2026.