The tragic boating accident at Lake Tahoe on Saturday that killed eight people, including a Bay Area tech executive, began with a mother’s birthday celebration that turned deadly when an unusual and violent summer storm generated 8-foot waves and 35 mph gusts of wind, capsizing a boat full of family and friends.

There were 10 people aboard the 27-foot powerboat in southwest Lake Tahoe, when a powerful thunderstorm rolled in Saturday afternoon, rapidly worsening conditions on the lake.