Cumulonimbus Clouds, or thunderheads, are most likely to form over San Diego County's deserts and mountains during the latter part of the summer season, beginning about mid-July. The clouds appear by midafternoon — often the result of moist, tropical air entering the county from the south or southeast. If intense, these cloud buildups are accompanied by enough rain to flood the desert washes and mountain drainages. When the weather pattern allows the movement of moist air beyond the mountain barriers, even coastal San Diego County can experience the cool spatter of raindrops and spectacular evening lightning displays.
Elderberry, a common bush or small tree found from San Diego County’s coastal canyons to the mountain slopes around Julian and Palomar, is in fruit this month. The branches carry myriads of tiny bluish fruits covered with a white powder. The fruits have traditionally been used for drinks and preserves.