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Weather & Climate in South San Francisco, CA

Temperature, precipitation, air quality, natural hazards, and monthly weather data.

South San Francisco enjoys a temperate climate with an average annual temperature of 59°F (15°C). Winters average 51°F in January while summers reach 64°F in July / relatively mild seasonal variation. The area gets 330 sunny days per year, well above the U.S. average of 205 / making it one of the sunnier locations in the country. Annual precipitation totals 19.6 inches (drier than the 38-inch national average). Air quality is rated Good with a median AQI of 48. The city sits at an elevation of 10 feet.

Temperature

51°F Jan (11°C) 64°F Jul (18°C)
Annual Average58.7°F
9% above US avg
January Average51°F (11°C)
July Average64°F (18°C)
Sunny Days330 days/yr

Geography

Elevation10 ft (3 m)
Area30.2 sq mi (78.1 km²)
Population Density7,009/sq mi
Coordinates37.6551°N, 122.3762°W
TimezoneAmerica/Los_Angeles
CountySan Mateo County County
Nearest AirportSan Francisco International (SFO)
3 miles away

Precipitation & Snow

Annual Rainfall 19.6"
48% below US avg
Wettest Month (Jan) 5.94"
Driest Month (Jul) 0.08"

Air Quality

AQI Median48.0
RatingGood

Natural Hazard Risk

Overall RiskRelatively High
Risk Score99.2 / 100
Social Vulnerability20.5 / 100
Community Resilience97.6 / 100

Hazard Breakdown

Tornado Relatively Low
Earthquake Relatively High
Wildfire Relatively Moderate
Flood Relatively High
Hail Very Low
Strong Wind Relatively Low
Heat Wave Relatively Moderate
Winter Weather Very Low
Lightning Relatively Moderate
Drought Relatively High
Cold Wave No Rating
Landslide Relatively High
Coastal Flood Relatively High
Tsunami Relatively Moderate
Source: FEMA National Risk Index v1.20 (Dec 2025)

Earthquake History

5,544 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 63 km 11 km
Apr 18, 1990 5 km NNW of Aromas, California M5.4 103 km 5 km
Aug 12, 1998 10 km SW of Ridgemark, California M5.1 129 km 9 km
Apr 18, 1990 4 km E of Interlaken, California M5.1 99 km 7 km
Jan 16, 1993 9 km E of Gilroy, California M4.9 107 km 7 km
Apr 18, 1990 4 km NNW of Aromas, California M4.9 103 km 6 km
Sep 3, 2000 5 km WSW of Yountville, California M4.9 81 km 9 km
Apr 19, 1996 2 km E of Aromas, California M4.9 109 km 5 km
May 14, 2002 5 km SSW of Gilroy, California M4.9 103 km 7 km
Sep 4, 1995 13 km SW of Middletown, California M4.8 119 km 7 km
May 12, 2006 7 km W of Cobb, California M4.7 135 km 4 km
May 21, 1996 8 km ESE of East Foothills, California M4.7 66 km 8 km
Apr 18, 1990 4 km N of Aromas, California M4.7 104 km 4 km
Aug 11, 1993 14 km ESE of Alum Rock, California M4.7 72 km 9 km
Jan 2, 2025 4 km NW of Cobb, CA M4.7 137 km 1 km
Aug 18, 1999 0 km S of Bolinas, California M4.6 39 km 8 km
Mar 24, 1991 1 km NNE of Interlaken, California M4.6 96 km 15 km
Jan 11, 2000 6 km N of Geyserville, California M4.6 133 km 6 km
Feb 18, 2004 4 km WNW of Cobb, California M4.6 136 km 3 km
Jan 12, 2014 8 km W of Cobb, California M4.5 134 km 2 km
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.

Tornado History

49 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF2. Total: 9 injuries.

Date Rating Distance Path Fatalities
May 5, 1998 EF2 44 km 0.6 mi 0
Jun 1, 1958 EF2 87 km 15.0 mi 0
Jan 11, 1951 EF2 39 km 5.7 mi 0
Dec 14, 2024 EF1 74 km 0.3 mi 0
Mar 18, 2011 EF1 93 km 0.1 mi 0
Jan 23, 2010 EF1 61 km 1.6 mi 0
Mar 20, 2005 EF1 4 km 3.0 mi 0
Dec 20, 2001 EF1 93 km 0.5 mi 0
Dec 5, 1998 EF1 93 km 1.5 mi 0
May 5, 1998 EF1 38 km 0.3 mi 0
Dec 23, 1996 EF1 82 km 6.0 mi 0
Dec 2, 1992 EF1 95 km 7.5 mi 0
Dec 2, 1992 EF1 92 km 1.0 mi 0
Feb 27, 1983 EF1 93 km 0.8 mi 0
Jan 14, 1980 EF1 48 km 0.3 mi 0
Apr 1, 1965 EF1 91 km 0.1 mi 0
Apr 1, 1958 EF1 5 km 0.2 mi 0
Jan 6, 2019 EF0 84 km 0.5 mi 0
Jan 6, 2019 EF0 83 km 0.1 mi 0
Apr 27, 2016 EF0 98 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 25 km
1989 N. CALIFORNIA Earthquake 1.0 m 62 82 km
1856 N. CALIFORNIA Eruption + Earthquake 0.6 m — 19 km
1906 N. CALIFORNIA Eruption + Earthquake 0.1 m — 12 km
1865 N. CALIFORNIA Eruption + Earthquake — — 66 km
Source: NOAA/NCEI Historical Tsunami Database.

Nearby Volcanoes

1 volcano within 200 km. Closest: Clear Lake (150 km).

Name Type Elevation Last Eruption Distance
Clear Lake Volcanic field 1,439 m (4,721 ft) Unknown 150 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 79 km
2020 CZU AUG LIGHTNING 85,894 58 km
2017 NUNS 56,883 78 km
2017 ATLAS 51,664 80 km
2007 LICK 47,424 97 km
2006 CANYON 36,851 97 km
1988 MILLER 35,750 90 km
2024 CORRAL 16,138 81 km
2009 CORRAL 12,006 79 km
1995 VISION 11,931 61 km
1985 LEXINGTON 11,550 70 km
2015 WRAGG 8,455 96 km
2009 LOCKHEED 8,287 65 km
2003 BIRD 7,727 93 km
1984 SITE 300 3 6,911 79 km
2005 TESLA 6,638 71 km
2003 DEL PUERTO 6,441 89 km
2006 MIDWAY 6,243 75 km
2003 DEVIL 4,975 73 km
2020 WOODWARD 4,952 57 km
Source: NIFC/IRWIN Wildfire Records (100+ acres).

Monthly Weather

Month Avg Temperature Precipitation Summary
January 51°F (11°C) 5.9 in Wettest
February 52°F (11°C) 4.9 in
March 53°F (11°C) 4.5 in
April 55°F (13°C) 1.9 in
May 57°F (14°C) 0.6 in
June 59°F (15°C) 0.2 in
July 64°F (18°C) 0.1 in Warmest, Driest
August 62°F (17°C) 0.1 in
September 63°F (17°C) 0.4 in
October 60°F (16°C) 1.7 in
November 54°F (12°C) 4.1 in
December 50°F (10°C) 4.6 in Coldest

South San Francisco has a seasonal temperature swing of 14°F / from 50°F in December to 64°F in July. Total annual precipitation is 28.9 inches, with January being the wettest month (5.9") and July the driest (0.1").

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