Rain and lightning in the Bay Area forecast: Is this normal? [SFGate, San Francisco] Jul. 26—A strong monsoonal surge will bring a mix of wet and dry thunderstorms to California this week, increasing the risk of wildfire ignitions at a time when multiple large blazes are already tearing across a parched landscape. While there’s a high chance for thunderstorms in the Sierra Nevada, the probability in the San Francisco Bay Area is slight though the risk is high, the National Weather Service said. “It takes just one spark to start a wildfire,” said Geri Diaz, a forecaster with the weather service.