Historical weather data, all-time temperature records, and monthly climate averages for San Mateo, CA. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4 in San Mateo runs mild, with an average high of 64° and low of 47° across 80 years of records. There's a roughly 1-in-4 chance of rain today, though the range of outcomes is wide — this date has seen everything from a 40° chill in 1950 to a 82° scorcher in 1985.
San Mateo's weather has some real extremes hiding beneath its temperate reputation — the thermometer has swung from a brutal 24° in December 1972 all the way to 105° during a June 2000 heat event. The wettest single day on record dumped 5.59 inches on January 4, 1982, a reminder that Bay Area winters can punch hard.
San Mateo is warmest in late summer, with the week of August 27–September 2 topping out at an average 74° — noticeably warmer than July thanks to the marine layer burning off later in the season. Winter is mild but wet, with December's final week averaging over an inch of rain and January highs sitting around 55°. If you're chasing sunshine and warmth, September is your best bet.