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Weather & Climate in Portola Valley, CA
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Portola Valley enjoys a temperate climate with an average annual temperature of 57°F (14°C). Winters average 48°F in January while summers reach 69°F in July. The area gets 305 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 42.2 inches. Air quality is rated Good with a median AQI of 48. The city sits at an elevation of 1,015 feet.
Temperature
48°F Jan (9°C)
69°F Jul (21°C)
| Annual Average | 57.1°F |
| 6% above US avg | |
| January Average | 48°F (9°C) |
| July Average | 69°F (21°C) |
| Sunny Days | 305 days/yr |
Geography
| Elevation | 1,015 ft (309 m) |
| Area | 9.1 sq mi (23.5 km²) |
| Population Density | 477/sq mi |
| Coordinates | 37.3652°N, 122.2327°W |
| Timezone | America/Los_Angeles |
| County | San Mateo County County |
| Nearest Airport | Norman Y Mineta San Jose International (SJC) 17 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 48.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively High |
| Risk Score | 99.2 / 100 |
| Social Vulnerability | 20.5 / 100 |
| Community Resilience | 97.6 / 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
4,064 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 | 95 km | 11 km |
| Apr 18, 1990 | 5 km NNW of Aromas, California | M5.4 | 70 km | 5 km |
| Apr 18, 1990 | 4 km E of Interlaken, California | M5.1 | 66 km | 7 km |
| Aug 12, 1998 | 10 km SW of Ridgemark, California | M5.1 | 96 km | 9 km |
| Jan 16, 1993 | 9 km E of Gilroy, California | M4.9 | 78 km | 7 km |
| Sep 3, 2000 | 5 km WSW of Yountville, California | M4.9 | 114 km | 9 km |
| Apr 23, 1995 | 22 km NNE of Soledad, California | M4.9 | 125 km | 7 km |
| Apr 18, 1990 | 4 km NNW of Aromas, California | M4.9 | 70 km | 6 km |
| Apr 19, 1996 | 2 km E of Aromas, California | M4.9 | 77 km | 5 km |
| May 14, 2002 | 5 km SSW of Gilroy, California | M4.9 | 72 km | 7 km |
| May 21, 1996 | 8 km ESE of East Foothills, California | M4.7 | 45 km | 8 km |
| Apr 18, 1990 | 4 km N of Aromas, California | M4.7 | 72 km | 4 km |
| Aug 11, 1993 | 14 km ESE of Alum Rock, California | M4.7 | 49 km | 9 km |
| Aug 27, 2011 | 21 km NE of Soledad, California | M4.6 | 128 km | 8 km |
| Mar 24, 1991 | 1 km NNE of Interlaken, California | M4.6 | 63 km | 15 km |
| Aug 18, 1999 | 0 km S of Bolinas, California | M4.6 | 72 km | 8 km |
| Sep 19, 2023 | 15 km SW of Westley, CA | M4.5 | 83 km | 4 km |
| Jan 12, 2011 | 9 km SSE of San Juan Bautista, California | M4.5 | 93 km | 8 km |
| Aug 3, 2006 | 5 km W of Glen Ellen, California | M4.5 | 115 km | 9 km |
| Apr 4, 2023 | 1km NNW of Tres Pinos, CA | M4.4 | 102 km | 10 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
40 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF2. Total: 10 injuries.
| Date | Rating | Distance | Path | Fatalities |
| May 5, 1998 | EF2 | 18 km | 0.6 mi | 0 |
| Mar 11, 1985 | EF2 | 94 km | 0.5 mi | 0 |
| Jan 11, 1951 | EF2 | 10 km | 5.7 mi | 0 |
| Dec 14, 2024 | EF1 | 39 km | 0.3 mi | 0 |
| Jan 23, 2010 | EF1 | 74 km | 1.6 mi | 0 |
| Mar 20, 2005 | EF1 | 36 km | 3.0 mi | 0 |
| Dec 20, 2001 | EF1 | 60 km | 0.5 mi | 0 |
| May 5, 1998 | EF1 | 10 km | 0.3 mi | 0 |
| Dec 6, 1992 | EF1 | 91 km | 1.0 mi | 0 |
| Dec 6, 1992 | EF1 | 95 km | 7.0 mi | 0 |
| Jan 14, 1980 | EF1 | 34 km | 0.3 mi | 0 |
| Apr 1, 1965 | EF1 | 58 km | 0.1 mi | 0 |
| Apr 1, 1958 | EF1 | 30 km | 0.2 mi | 0 |
| Jan 6, 2019 | EF0 | 48 km | 0.1 mi | 0 |
| Jan 6, 2019 | EF0 | 49 km | 0.5 mi | 0 |
| Jan 6, 2016 | EF0 | 89 km | 0.6 mi | 0 |
| Dec 22, 2012 | EF0 | 65 km | 1.1 mi | 0 |
| Apr 11, 2012 | EF0 | 98 km | 0.3 mi | 0 |
| Apr 7, 2011 | EF0 | 98 km | 0.1 mi | 0 |
| Apr 14, 2007 | EF0 | 69 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 | 48 km |
| 1856 | N. CALIFORNIA | Eruption + Earthquake | 0.6 m | — | 16 km |
| 1906 | N. CALIFORNIA | Eruption + Earthquake | 0.1 m | — | 44 km |
| 1865 | N. CALIFORNIA | Eruption + Earthquake | — | — | 35 km |
Source: NOAA/NCEI Historical Tsunami Database.
Nearby Volcanoes
1 volcano within 200 km. Closest: Clear Lake (185 km).
| Name | Type | Elevation | Last Eruption | Distance |
| Clear Lake | Volcanic field | 1,439 m (4,721 ft) | Unknown | 185 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 | 66 km |
| 2020 | CZU AUG LIGHTNING | 85,894 | 24 km |
| 2007 | LICK | 47,424 | 73 km |
| 2006 | CANYON | 36,851 | 79 km |
| 2003 | ANNIE | 17,383 | 89 km |
| 2024 | CORRAL | 16,138 | 75 km |
| 2009 | CORRAL | 12,006 | 70 km |
| 1995 | VISION | 11,931 | 94 km |
| 1985 | LEXINGTON | 11,550 | 37 km |
| 2009 | LOCKHEED | 8,287 | 32 km |
| 2003 | BIRD | 7,727 | 82 km |
| 1984 | SITE 300 3 | 6,911 | 74 km |
| 2005 | TESLA | 6,638 | 68 km |
| 2003 | DEL PUERTO | 6,441 | 74 km |
| 2006 | MIDWAY | 6,243 | 71 km |
| 2020 | CREWS | 5,802 | 79 km |
| 2003 | DEVIL | 4,975 | 60 km |
| 2020 | WOODWARD | 4,952 | 90 km |
| 2003 | JUMP | 4,817 | 63 km |
| 2016 | LOMA | 4,380 | 46 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 48°F (9°C) | 5.4 in | Coldest, Wettest |
| February | 51°F (11°C) | 4.4 in | |
| March | 52°F (11°C) | 4.3 in | |
| April | 55°F (13°C) | 1.9 in | |
| May | 58°F (15°C) | 0.5 in | |
| June | 62°F (17°C) | 0.2 in | |
| July | 69°F (21°C) | 0.1 in | Warmest, Driest |
| August | 66°F (19°C) | 0.1 in | |
| September | 65°F (18°C) | 0.4 in | |
| October | 61°F (16°C) | 1.5 in | |
| November | 54°F (12°C) | 3.9 in | |
| December | 49°F (9°C) | 4.3 in |
Portola Valley has a seasonal temperature swing of 21°F / from 48°F in January to 69°F in July. Total annual precipitation is 26.9 inches, with January being the wettest month (5.4") and July the driest (0.1").