The weather on July 30, 2016
A powerful storm dumped more than 6 inches of rain on parts of Ellicott City in less than two hours on July 30, 2016, triggering catastrophic flash flooding that killed two people, devastated the town’s historic Main Street and became one of Maryland’s most destructive weather disasters in recent history.
The National Weather Service said a nearly stationary band of thunderstorms stalled over central Maryland between 6:45 p.m. and 8:30 p.m., producing intense rainfall that overwhelmed streams and storm drains.
The heaviest rain fell between 7:45 p.m. and 8 p.m., while a flash flood warning had been issued at 7:18 p.m. Reports of flooding began minutes later as water rapidly rushed downhill into Old Ellicott City.
The storm’s impact was magnified by Ellicott City’s geography
Built in a narrow valley where several streams converge before reaching the Patapsco River, the historic district funneled runoff into Main Street. Water quickly transformed roadways into fast-moving currents that swept away vehicles, damaged buildings, and left businesses buried in mud and debris.
Weather officials estimated that localized rainfall exceeded 6 inches, with much of it falling within 90 minutes. According to the National Weather Service’s rainfall frequency analysis, the event had an annual probability of 0.1% or less for several rainfall durations, making it an exceptionally rare occurrence.
A storm like this has about a one-in-1,000 chance of occurring in any given year.
The Patapsco River rose
The river rose more than 13 feet in less than 2 hours, including a surge of more than 2 feet in just five minutes during the height of the flooding. Emergency officials said the rapid rise coincided with the most severe flooding across downtown.
A post-flood survey found water marks reaching 6 to 8 feet inside buildings near the lower end of Main Street. Roads, sidewalks and infrastructure sustained extensive damage, while the floodwaters swept away the town’s iconic clock and a historic flood marker attached to the railroad bridge. Hundreds of vehicles were damaged or destroyed, and many historic structures required extensive repairs.
The disaster prompted renewed attention to flash flood preparedness, emergency warning systems and stormwater management throughout Howard County.
Meteorologists and emergency managers continue to study the event as an example of how extreme rainfall and steep terrain can combine to produce life-threatening flash flooding in a matter of minutes.
Graphic video: as the waters rose people stranded called 911 for help
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