Weather & Climate in Port Costa, CA
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Port Costa enjoys a temperate climate with an average annual temperature of 62°F (17°C). Winters average 49°F in January while summers reach 73°F in July. Annual precipitation totals 16.1 inches (drier than the 38-inch national average). Air quality is rated Good with a median AQI of 28 / among the cleanest air in the country. 86% of days have good air quality. The city sits at an elevation of 171 feet.
Temperature
49°F Jan (10°C)
73°F Jul (23°C)
| Annual Average | 62.0°F |
| 15% above US avg | |
| January Average | 49°F (10°C) |
| July Average | 73°F (23°C) |
Geography
| Elevation | 171 ft (52 m) |
| Area | 0.2 sq mi (0.4 km²) |
| Population Density | 1,213/sq mi |
| Coordinates | 38.0445°N, 122.1849°W |
| Timezone | America/Los_Angeles |
| County | Marin County County |
| Nearest Airport | Metro Oakland International (OAK) 22 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 28.0 |
| Rating | Good |
| Good Days % | 86.3% |
| Unhealthy Days | 0 |
Natural Hazard Risk
| Overall Risk | Relatively High |
| Risk Score | 96.4 / 100 |
| Social Vulnerability | 24.7 / 100 |
| Community Resilience | 99.2 / 100 |
Hazard Breakdown
| Tornado | Very Low |
| Earthquake | Relatively High |
| Wildfire | Relatively Moderate |
| Flood | Relatively High |
| Hail | Very Low |
| Strong Wind | Very Low |
| Heat Wave | Relatively Low |
| Winter Weather | Very Low |
| Lightning | Relatively Low |
| Drought | Relatively Low |
| Cold Wave | No Rating |
| Landslide | Relatively High |
| Coastal Flood | Very High |
| Tsunami | Relatively Moderate |
| Volcano | Very Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
4,900 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M6.0.
| Aug 24, 2014 | The 2014 South Napa, California Earthquake | M6.0 | 22 km | 11 km |
| Apr 18, 1990 | 5 km NNW of Aromas, California | M5.4 | 132 km | 5 km |
| Apr 18, 1990 | 4 km E of Interlaken, California | M5.1 | 129 km | 7 km |
| Jan 16, 1993 | 9 km E of Gilroy, California | M4.9 | 131 km | 7 km |
| Apr 18, 1990 | 4 km NNW of Aromas, California | M4.9 | 132 km | 6 km |
| May 14, 2002 | 5 km SSW of Gilroy, California | M4.9 | 131 km | 7 km |
| Apr 19, 1996 | 2 km E of Aromas, California | M4.9 | 138 km | 5 km |
| Sep 3, 2000 | 5 km WSW of Yountville, California | M4.9 | 42 km | 9 km |
| Sep 4, 1995 | 13 km SW of Middletown, California | M4.8 | 86 km | 7 km |
| May 12, 2006 | 7 km W of Cobb, California | M4.7 | 102 km | 4 km |
| Apr 18, 1990 | 4 km N of Aromas, California | M4.7 | 133 km | 4 km |
| May 21, 1996 | 8 km ESE of East Foothills, California | M4.7 | 86 km | 8 km |
| Aug 11, 1993 | 14 km ESE of Alum Rock, California | M4.7 | 93 km | 9 km |
| Jan 2, 2025 | 4 km NW of Cobb, CA | M4.7 | 102 km | 1 km |
| Aug 18, 1999 | 0 km S of Bolinas, California | M4.6 | 47 km | 8 km |
| Mar 24, 1991 | 1 km NNE of Interlaken, California | M4.6 | 127 km | 15 km |
| Jan 11, 2000 | 6 km N of Geyserville, California | M4.6 | 103 km | 6 km |
| Feb 18, 2004 | 4 km WNW of Cobb, California | M4.6 | 102 km | 3 km |
| Jan 12, 2014 | 8 km W of Cobb, California | M4.5 | 102 km | 2 km |
| Sep 19, 2023 | 15 km SW of Westley, CA | M4.5 | 103 km | 4 km |
Source: USGS Earthquake Catalog (M2.5+, 1990-2025). Sorted by magnitude.
Tornado History
69 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF2. Total: 4 injuries.
| Date | Rating | Distance | Path | Fatalities |
| May 5, 1998 | EF2 | 76 km | 0.6 mi | 0 |
| Feb 7, 1978 | EF2 | 97 km | 1.9 mi | 0 |
| Jun 1, 1958 | EF2 | 74 km | 15.0 mi | 0 |
| Jan 11, 1951 | EF2 | 75 km | 5.7 mi | 0 |
| Mar 18, 2011 | EF1 | 64 km | 0.1 mi | 0 |
| Jan 23, 2010 | EF1 | 40 km | 1.6 mi | 0 |
| Mar 20, 2005 | EF1 | 49 km | 3.0 mi | 0 |
| Dec 5, 1998 | EF1 | 64 km | 1.5 mi | 0 |
| May 5, 1998 | EF1 | 74 km | 0.3 mi | 0 |
| Dec 23, 1996 | EF1 | 69 km | 6.0 mi | 0 |
| Feb 22, 1996 | EF1 | 74 km | 1.0 mi | 0 |
| Dec 2, 1992 | EF1 | 74 km | 7.5 mi | 0 |
| Dec 2, 1992 | EF1 | 69 km | 1.0 mi | 0 |
| Dec 2, 1992 | EF1 | 79 km | 3.0 mi | 0 |
| Apr 19, 1988 | EF1 | 92 km | 0.2 mi | 0 |
| Feb 27, 1983 | EF1 | 64 km | 0.8 mi | 0 |
| Jan 14, 1980 | EF1 | 68 km | 0.3 mi | 0 |
| May 31, 1967 | EF1 | 78 km | 0.1 mi | 0 |
| Nov 10, 1964 | EF1 | 76 km | 1.0 mi | 0 |
| Apr 1, 1958 | EF1 | 49 km | 0.2 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950-2024, US only).
Tsunami History
5 tsunamis recorded within 500 km. Highest wave on record: 4.5 m (15 ft).
| Year | Location | Cause | Max Wave | Deaths | Distance |
| 1868 | N. CALIFORNIA | Eruption + Earthquake | 4.5 m | 30 | 39 km |
| 1989 | N. CALIFORNIA | Earthquake | 1.0 m | 62 | 115 km |
| 1856 | N. CALIFORNIA | Eruption + Earthquake | 0.6 m | - | 61 km |
| 1906 | N. CALIFORNIA | Eruption + Earthquake | 0.1 m | - | 47 km |
| 1865 | N. CALIFORNIA | Eruption + Earthquake | - | - | 97 km |
Source: NOAA/NCEI Historical Tsunami Database.
Nearby Volcanoes
1 volcano within 200 km. Closest: Clear Lake (115 km).
| Name | Type | Elevation | Last Eruption | Distance |
| Clear Lake | Volcanic field | 1,439 m (4,721 ft) | Unknown | 115 km |
Source: Smithsonian Institution Global Volcanism Program (GVP).
Wildfire History
20 wildfires (100+ acres) recorded within 100 km. Largest: SCU LIGHTNING COMPLEX (405,787 acres, 2020).
| Year | Name | Acres Burned | Distance |
| 2020 | SCU LIGHTNING COMPLEX | 405,787 | 86 km |
| 2020 | HENNESSEY | 314,241 | 65 km |
| 2015 | ROCKY | 96,125 | 99 km |
| 2018 | COUNTY | 92,450 | 71 km |
| 2020 | CZU AUG LIGHTNING | 85,894 | 100 km |
| 2019 | KINCADE | 77,780 | 87 km |
| 2015 | VALLEY | 77,507 | 91 km |
| 2020 | GLASS | 68,020 | 65 km |
| 2017 | NUNS | 56,883 | 44 km |
| 2020 | WALLBRIDGE | 55,194 | 96 km |
| 2017 | ATLAS | 51,664 | 36 km |
| 2004 | RUMSEY | 39,335 | 80 km |
| 1999 | SIXTEEN | 37,162 | 85 km |
| 2017 | TUBBS | 36,981 | 73 km |
| 1988 | MILLER | 35,750 | 44 km |
| 2024 | CORRAL | 16,138 | 78 km |
| 2006 | ZAM ASSIST | 14,404 | 83 km |
| 2004 | GEYSERS | 12,075 | 91 km |
| 2009 | CORRAL | 12,006 | 79 km |
| 1995 | VISION | 11,931 | 59 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 49°F (10°C) | 3.2 in | Coldest, Wettest |
| February | 53°F (12°C) | 3.2 in | |
| March | 57°F (14°C) | 2.3 in | |
| April | 60°F (16°C) | 1.1 in | |
| May | 65°F (19°C) | 0.5 in | |
| June | 71°F (21°C) | 0.2 in | |
| July | 73°F (23°C) | 0.0 in | Driest |
| August | 74°F (23°C) | 0.0 in | Warmest |
| September | 72°F (22°C) | 0.1 in | |
| October | 65°F (19°C) | 0.7 in | |
| November | 56°F (13°C) | 1.6 in | |
| December | 50°F (10°C) | 3.2 in |
Port Costa has a seasonal temperature swing of 24°F / from 49°F in January to 74°F in August. Total annual precipitation is 16.1 inches, with January being the wettest month (3.2") and July the driest (0.0").