From XC Skys on a classic day 9-27-18 starting at 9 am till 6 pm.
Note that the Eastern side of the Santa Ana Mts / Santiago Saddleback coastal range (that block & hold back the westerly winds and also referred to the E's Back Range) typically develop 1st before the flats heat up to be workable. Many times, it becomes a patience & waiting game while trying to hold onto altitude before crossing over into the flats. A lot of times, it is beneficial to hold onto the Back Range until the West pushes through. Once the west pushes through, it is time to go with it and try to stay slightly ahead of it as a tail wind, as the cooler west diminishes the Back Range's productivity, and the Flats turn on.