The National Weather Service (NWS) issued a red flag warning for parts of northern California on September 9.
In an update, the NWS said forecasted thunderstorms were a result of two weather systems converging over northern California, with a sub tropical flow from the south meeting a system from the Gulf of Alaska.
This convergence could result in high-based thunderstorm as rain evaporates before the hitting the ground leaving “dry thunderstorms” and lightning, the NWS said.
Video posted by Craig Philpott shows a bolt of lightning illuminating the night sky in Napa. Credit: Craig Philpott via Storyful