Emergency workers gather at the scene of a tornado - in Sunnyvale, Calif., not the Midwest. A small twister tore through a neighborhood of the Silicon Valley community Monday, uprooting trees, damaging roofs and shattering windows. One woman was slightly injured. Twisters are relatively rare in California, although there have been 20 to 30 in the San Francisco Bay area in the past four decades, said meteorologist Dan Weygand. "Compared to Texas, the chances of getting hit by a tornado here are almost negligible," Weygand said. About 1,500 customers lost power in Sunnyvale, along with more than 4,000 in nearby Los Altos, Pacific Gas & Electric said.