Southern California maintains a fairly consistent climate throughout the year. As such, the average temperature in San Diego, CA, doesn't fluctuate much. The average high of 77 degrees Fahrenheit in August drops slightly more than 10 degrees to an average high of 65 degrees in January. It never really gets cold in San Diego, with typical winter (December-March) lows around 50 degrees Fahrenheit. Even with a steady year-round temperature, the best months to visit San Diego are before or after the busy summer (June-September) season. April, May, September, and October are when you'll find it easiest to explore San Diego's landmarks and neighborhoods with fewer crowds and near-optimal weather.