Millions across the East Coast are bracing for another round of severe storms and potential flash flooding.A flash flood emergency was issued Saturday evening near Washington D.C., where emergency crews rescued several drivers trapped in rising water.In southern Maryland, entire roads were submerged, halting traffic and posing grave risks.One video from northern D.C. showed a car submerged in nearly a foot of water, recorded by resident Michael Starr Hopkins.Forecasters warned that more storms are expected Sunday, worsening conditions in already saturated areas.Chapel Hill, North Carolina, is among the most vulnerable having recently been battered by Tropical Storm Chantel.North Carolina Governor Josh Stein declared a state of emergency that now covers 13 counties in the state.Further north, the New York City area faces a level 2 of 5 risk for severe storms.Earlier this week, floodwaters poured into Manhattan subway stations, prompting flash flood warnings.Two people died in New…..