National Aeronautics and Space Administration

Beginning on July 21, 2018, an atmospheric river, a narrow stream of enhanced water vapor transport, positioned itself over the region, resulting in record daily rainfall totals and extensive flash flood warnings as the entire months’ worth of precipitation fell in a matter of days. This rainfall event was clearly captured by GMAO’s Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2). Throughout the multi-day precipitation event, a sub-tropical high pressure system was present over the Atlantic Ocean and a digging trough extended sout h int o the Gulf of Mexico and north to the east coast. Both features helped guide the transport of water vapor into the Maryland area, as evident in this corresponding animation. Read more.