| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 14.2° | 7.6° | 100.3mm | 11 | 59 |
| February | 15.6° | 8° | 91.3mm | 10.1 | 66 |
| March | 16.9° | 8.9° | 68.6mm | 10.5 | 69 |
| April | 18.2° | 9.7° | 34.2mm | 6 | 82 |
| May | 19.6° | 11.2° | 11.6mm | 2.9 | 93 |
| June | 21.5° | 12.4° | 3.1mm | 1 | 98 |
| July | 22° | 13.2° | 0mm | 0 | 100 |
| August | 22.6° | 13.8° | 0.7mm | 0.4 | 99 |
| September | 23.4° | 13.7° | 2mm | 1 | 98 |
| October | 21.9° | 12.3° | 22.1mm | 3 | 94 |
| November | 17.6° | 9.6° | 51.9mm | 7.5 | 77 |
| December | 14.3° | 7.6° | 117.3mm | 11.4 | 59 |
January in San Mateo averages a daily high of 14.2°C with nights around 7.6°C. Expect roughly 11 wet days totalling 100.3mm. Generally workable, with some weather to plan around.
February in San Mateo averages a daily high of 15.6°C with nights around 8°C. Expect roughly 10.1 wet days totalling 91.3mm. Generally workable, with some weather to plan around.
March in San Mateo averages a daily high of 16.9°C with nights around 8.9°C. Expect roughly 10.5 wet days totalling 68.6mm. Generally workable, with some weather to plan around.
April in San Mateo averages a daily high of 18.2°C with nights around 9.7°C. Expect roughly 6 wet days totalling 34.2mm. Comfortable conditions for being outdoors all day.
May in San Mateo averages a daily high of 19.6°C with nights around 11.2°C. Rain is rare — about 2.9 wet days and 11.6mm across the month. Comfortable conditions for being outdoors all day.
June in San Mateo averages a daily high of 21.5°C with nights around 12.4°C. Rain is rare — about 1 wet days and 3.1mm across the month. Comfortable conditions for being outdoors all day.
July in San Mateo averages a daily high of 22°C with nights around 13.2°C. Rain is rare — about 0 wet days and 0mm across the month. Comfortable conditions for being outdoors all day.
August in San Mateo averages a daily high of 22.6°C with nights around 13.8°C. Rain is rare — about 0.4 wet days and 0.7mm across the month. Comfortable conditions for being outdoors all day.
September in San Mateo averages a daily high of 23.4°C with nights around 13.7°C. Rain is rare — about 1 wet days and 2mm across the month. Comfortable conditions for being outdoors all day.
October in San Mateo averages a daily high of 21.9°C with nights around 12.3°C. Expect roughly 3 wet days totalling 22.1mm. Comfortable conditions for being outdoors all day.
November in San Mateo averages a daily high of 17.6°C with nights around 9.6°C. Expect roughly 7.5 wet days totalling 51.9mm. Comfortable conditions for being outdoors all day.
December in San Mateo averages a daily high of 14.3°C with nights around 7.6°C. Expect roughly 11.4 wet days totalling 117.3mm. Generally workable, with some weather to plan around.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. San Mateo peaks at 100.
Based on 30 years of records, May–October scores highest for comfort in San Mateo, balancing daytime temperature against rainfall.
September is the warmest, averaging a daily high of 23.4°C.
December is the wettest, averaging 117.3mm of rain across roughly 11.4 wet days.
January is the coolest month, with average daily highs around 14.2°C.