Locals have long described 1972’s Hurricane Agnes as the worst storm in memory to pass through historic Ellicott City, Md., a small historic mill town nestled at the convergence of the Patapsco River and three tributary streams in central Howard County south of Baltimore. A marker at the base of Main Street shows that floodwaters reached 14.5 ft during Agnes. The only other time water reached that high was in 1868, when waters from the engorged Patapsco River surged to 21.5 ft.

But two flash floods in 2016 and 2018—when water reached 27.14 ft and 27.03 ft, respectively—eclipsed local lore and changed the focus of conversation. County officials say the 2016 storm dumped 6 in. of rain in two hours; in 2018, it was 8 in.