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Millbrae, California climate

Csb Warm-summer Mediterranean

Millbrae has a mildly seasonal mild-temperate climate (Warm-summer Mediterranean, Köppen Csb). The hottest month is September with an average daily high near 24°C, while the coldest is January averaging around 7°C at night. Precipitation totals about 499 mm a year and is strongly seasonal — December alone averages 105 mm while July barely receives 0 mm.

☀️ Summers
Mild
Highs near 24°C in September.
About 4 days a year above 32 °C
❄️ Winters
Cool
Lows near 7°C in January.
🌧️ Rain
Fairly dry
About 499 mm of rain a year.
Wettest in December
⛅ Sky & trend
Partly cloudy
A roughly even mix of sun and cloud.
+0.7 °C vs 50 years ago

Temperature & precipitation

Daily high–low temperature range with the monthly average, plus monthly precipitation · 1991–2020 normals · hover a month for the exact figures TEMPERATURE °C 0°10°20°30° PRECIPITATION (mm) 055110 JanAprJulOct

Clear vs cloudy days

Share of days each month that are clear, partly cloudy or cloudy · 1991–2020 · hover a month for the day counts 0%25%50%75%100% JanAprJulOct Cloudy Partly Cloudy Clear

Millbrae climate normals (1991–2020)

JanFebMarAprMayJunJulAugSepOctNovDec
Avg high (°C)141617192022232324221815
Avg temp (°C)111213141617181819171411
Avg low (°C)7891011121314131297
Precipitation (mm)9910169351240122052105
Jan – JunJanFebMarAprMayJun
Avg high (°C)141617192022
Avg temp (°C)111213141617
Avg low (°C)789101112
Precipitation (mm)991016935124
Jul – DecJulAugSepOctNovDec
Avg high (°C)232324221815
Avg temp (°C)181819171411
Avg low (°C)1314131297
Precipitation (mm)0122052105

How often — frequency of weather events

JanFebMarAprMayJunJulAugSepOctNovDec
Days with measurable rain (days)1111106310.00.40.93711
Days with high ≥ 32°C (days)———0.10.40.70.30.620.5——
Days with low ≤ 0°C (days)0.0——————————0.1
Jan – JunJanFebMarAprMayJun
Days with measurable rain (days)111110631
Days with high ≥ 32°C (days)———0.10.40.7
Days with low ≤ 0°C (days)0.0—————
Jul – DecJulAugSepOctNovDec
Days with measurable rain (days)0.00.40.93711
Days with high ≥ 32°C (days)0.30.620.5——
Days with low ≤ 0°C (days)—————0.1

Sky & atmosphere

JanFebMarAprMayJunJulAugSepOctNovDec
Cloud cover (%)606160555448585951475157
Clear days (≤ 30% cloud)767881044911108
Partly cloudy days (30–70%)981111111115141111109
Cloudy days (≥ 70%)1514141112912131091014
Relative humidity (%)848384848585868683808081
Wind speed (m/s)3.63.83.84.04.03.93.33.33.03.03.23.8
Jan – JunJanFebMarAprMayJun
Cloud cover (%)606160555448
Clear days (≤ 30% cloud)7678810
Partly cloudy days (30–70%)9811111111
Cloudy days (≥ 70%)15141411129
Relative humidity (%)848384848585
Wind speed (m/s)3.63.83.84.04.03.9
Jul – DecJulAugSepOctNovDec
Cloud cover (%)585951475157
Clear days (≤ 30% cloud)44911108
Partly cloudy days (30–70%)15141111109
Cloudy days (≥ 70%)12131091014
Relative humidity (%)868683808081
Wind speed (m/s)3.33.33.03.03.23.8

30-year delta table (1991–2020 minus 1981–2010, °F)

JanFebMarAprMayJunJulAugSepOctNovDec
Δ Max temp+1.7+1.3+1.3+0.9+0.7+0.9+0.6+0.7+1.2+1.9+1.4+1.6
Δ Avg temp+1.0+0.6+0.6+0.4+0.3+0.3+0.3+0.4+0.6+1.1+0.6+0.8
Δ Min temp+0.3-0.2-0.1+0.0+0.0-0.2-0.1+0.1+0.1+0.2-0.2+0.0
Jan – JunJanFebMarAprMayJun
Δ Max temp+1.7+1.3+1.3+0.9+0.7+0.9
Δ Avg temp+1.0+0.6+0.6+0.4+0.3+0.3
Δ Min temp+0.3-0.2-0.1+0.0+0.0-0.2
Jul – DecJulAugSepOctNovDec
Δ Max temp+0.6+0.7+1.2+1.9+1.4+1.6
Δ Avg temp+0.3+0.4+0.6+1.1+0.6+0.8
Δ Min temp-0.1+0.1+0.1+0.2-0.2+0.0
Methodology & sources

Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at San Francisco Intl AP (NOAA GHCN station USW00023234), about 3 km from the city centre.

Cloud, humidity, wind & sunshine — modelled estimates from NASA POWER, NASA's satellite-and-reanalysis climatology. This is the standard global source for atmospheric variables, which are not measured at most weather stations.

How we build these numbers →