Maryland Flood Event: A flood occurs throughout the Patapsco Valley, causing one death, destroying the entire first floors of buildings on Main Street in Ellicott City, and causing cars to overturn.

In the afternoon of May 27, 2018, after over 8 inches (20 cm) of rain in a span of two hours, the historic Main Street in Ellicott City, Maryland was flooded, just before the new flood emergency alert system was supposed to become operational. Flooding occurred throughout the Patapsco Valley, in the adjacent communities of Catonsville, Arbutus, and Elkridge, as well as the Jones Falls Valley in Baltimore.

The Patapsco Valley is a small valley surrounding the Patapsco River in central Maryland. The region is known for its historical significance as a major economic and industrial center in the eighteenth and nineteenth centuries.

Ellicott City is an unincorporated community and census-designated place in, and the county seat of, Howard County, Maryland, United States. Part of the Baltimore metropolitan area, its population was 75,947 at the 2020 census, making it the most populous unincorporated county seat in the United States.