The amount of rain predicted to hit the Houston area is more than three-times the heaviest rain event ever recorded in the DC region.
Tropical cyclone Agnes in 1972 dropped between 10 and 15 inches of rain and caused the most deadly flood in the Mid-Atlantic region. By comparison, Harvey is predicted to drop as much as 50-inches of rain in Houston.
The Washington area's biggest recorded flood was in 1936. That event combined 5 to 6 inches rainfall with an uncalculated volume of melting snow in the Potomac River basin including the highlands of West Virginia.
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In 2015 scientists at the Virginia Institute of Marine Science created a modern computer model that accurately depicted the 1936 event. An image of the 1936 flood zone showed much of Georgetown, Alexandria, Joint Base Bolling and the Navy Yard underwater. 1936 floodwaters reached the National Mall, according to the map.
There is only speculation what a Harvey-sized weather event in our region might do.
The VIMS computer model has the capability to make a prediction, but it has never been run for such an event because it is considered unthinkable, according to Dr. Harry V. Wang, who was the lead author on the 2015 modeling project.
Running the model requires up to 18-hours of supercomputer calculation time.