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 various drinks and preserves.
Cicadas, the insects that sound like tinny buzzsaws in the brush, have been putting up a racket around San Diego lately. Occasionally mistaken for the tail buzz of a rattlesnake, the sound is merely that of a male calling to potential mates. Some 30 species of cicadas inhabit San Diego County, but none are of the famous periodical type that emerge en masse every 13 or 17 years to serenade parts of the eastern United States.