A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. From Wikipedia
A 30–40 kt low-level jet in 2.0–2.25 inch precipitable water is focusing back-building bands that produce 2–3 inches per hour.
