At 7:13 p.m. on Tuesday, the National Weather Service issued an updated flash flood warning in effect until 9:30 p.m. for Lancaster County. "At 7:13 p.m., Local law enforcement reported thunderstorms producing heavy rain in Lancaster City. Understanding the differences between advisories, watches, and warningsFlash flood warning: Take action! A flash flood warning is issued when a flash flood is imminent or occurring. A flash flood is a sudden violent flood that can take from minutes to hours to develop.