Places recently hit hard -- like Kerrville, Texas, and Burnet, Texas -- are inside this heightened potential for flash flooding, with any heavy rain and flash flooding that occurs over or adjacent to these areas likely to flow downstream via rivers that run through or nearby these devastated areas.

Millions across the Northeast and Mid-Atlantic remain under flash flood warnings early Tuesday as slow-moving summer storms bring heavy showers to the East Coast, impacting transportation and leaving people stranded in vehicles on waterlogged roads.