Historical weather data, all-time temperature records, and monthly climate averages for San Dimas, CA. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
San Dimas sits in the San Gabriel Valley foothills, where summer heat can be relentless — the all-time record of 109° was set on July 22, 2006, a reminder of just how intense inland SoCal summers get. Today's date has its own chapter in that story.
San Dimas has seen everything from a scorching 109° in July 2006 to a bone-chilling 19° in March 1986 — a 90-degree swing that tells you this isn't your stereotypical mild Southern California spot. The inland foothills location means real heat in summer and occasional hard freezes in winter.
Summers run hot, with average highs peaking around 89-90° from late July through early August, while the mildest stretch comes late December when highs settle near 59°. Rainfall is concentrated in winter, with early January marking the wettest period of the year — though 'wet' is relative in this corner of LA County.