From <a href="http://www.civanonursery.net/2014/11/12/fall-colors-in-the-low-desert/">Civano Nursery</a>
Sycamores are already fading to yellow and brown.
Leaves are beginning to turn in coastal San Diego County’s riparian woodland and oak woodland habitats. In response to a relatively dry spring and summer, the summer-green crowns of willows and sycamores are already fading to yellow and brown. Beneath the oaks, the deciduous poison oak is flushing red. Some good places for autumn walks this month and next include San Clemente Canyon (Marian Bear) Park adjacent to Freeway 52, Los Peñasquitos Canyon Preserve north of Mira Mesa, and Wilderness Gardens Preserve County Park east of Pala in North County.
Low-Lying Temperature Inversions commonly occur in San Diego from late fall through early winter. During the night and morning hours, a meteorological condition often occurs in which the “normal” higher-you-go-the colder-it-gets trend is reversed. At such times cold marine air lies below a stable layer of warmer air originating from inland locales. Whenever moist air is trapped below a low-lying inversion layer, dense fog forms on or near the ground, and San Diego International Airport may be forced to suspend operations.