A flash flood is a rapid rise of water along a stream or in a low-lying urban area, the weather service said. Flash flooding can result from slow-moving thunderstorms, from numerous thunderstorms that develop repeatedly over the same area, or from heavy rains associated with tropical cyclones.

Social media users are spreading false claims that flash floods in Texas that killed more than 100 people over the Fourth of July holiday weekend were caused by weather modification.

All rivers in the Granite State are subject to flash flooding, though the risk level varies; only 3 counties are low risk, FEMA says.