My son, partner and I were driving east on Highway 24 snd passing the College Avenue exit on August 30, 2012. The overcast was heavy and usual for the Bay Area. At approximate 925pm my son, partner and I saw a green flash illuminate the sky above us and in a circular fashion and surround in a half mile in a circular pattern. Two more green flashes occurred two minutes apart from the 925pm event. The green was not distinct and did not have a resemblance of such aircraft that usually flies in the sky.