The best rule of thumb when visiting Brisbane, CA is to dress in layers and when you travel there, take a sweater or jacket. For instance, photos of a the summer concerts in the park held in August and early September show people wearing jackets in the late afternoon.
The least amount of rain and sunniest season in Brisbane in June through September. The most rain usually occurs in January and February when the city may see around 4.5 to 5 inches in a month.
The hottest, record setting temperatures in Brisbane have reached 106 degrees. Such hot spells are rare, so you'll be pretty safe in packing jackets even in the summer months.