...Tropical moisture will combine with a slow moving frontal system to produce very heavy rainfall. A mixture of slow moving storms and the potential for multiple rounds of convection will increase the risk of flash flooding... * WHAT...Flash flooding caused by excessive rainfall continues to be possible. * WHERE...The District of Columbia, across portions of Maryland, including the following areas, Anne Arundel, Calvert, Carroll, Cecil, Central and Southeast Howard, Central and Southeast Montgomery, Charles, Frederick MD, Northern Baltimore, Northwest Harford, Northwest Howard, Northwest Montgomery, Prince Georges, Southeast Harford, Southern Baltimore, St. Marys and Washington, Virginia, including the following areas, Albemarle, Arlington/Falls Church/Alexandria, Augusta, Central Virginia Blue Ridge, Central and Southeast Prince William/Manassas/Manassas Park, Clarke, Culpeper, Eastern Loudoun, Fairfax, Frederick VA, Greene, King George, Madison, Nelson, Northern Fauquier, Northern Virginia Blue Ridge, Northwest Prince William, Orange, Page, Rappahannock, Rockingham, Shenandoah, Southern Fauquier, Spotsylvania, Stafford, Warren and Western Loudoun, and panhandle West Virginia, including the following areas, Berkeley, Jefferson and Morgan. * WHEN...From 2 PM EDT this afternoon through this evening. * IMPACTS...Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Flooding may occur in poor drainage and urban areas. * ADDITIONAL DETAILS... - Showers and thunderstorms capable of producing heavy rainfall will move across the area this afternoon and evening. Rainfall rates up to 2 to 3 inches per hour are possible, which may lead to scattered instances of flash flooding where the heavy rain is slower moving and where multiple rounds of storms occurs. Storm total amounts up to 4 to 6 inches are possible where this occurs. - Please visit www.weather.gov/safety/flood for flood safety and preparedness information