Sep 9, 2018
Low pressure tracked to the west while a nearly stationary boundary was to the south. Warm and moist tropical air overran the surface cooler air in place, resulting in a moderate to heavy rainfall. Excess runoff from the rainfall led to flooding. One and a half to three inches of rain fell across northern Maryland late on the 8th into the 9th, followed by another one to three inches on the 9th into the 10th. This combination produced fairly widespread flooding, including of the mainstem rivers,
Source: NOAA National Weather Service Storm Events Database (event 787256). Narrative written by NWS staff at the time of the event.
This event is one of many recorded floods in Frederick County. See the full FEMA flood zone map, NFIP claim totals, and disaster history for the area.