The computer forecasting models have shown a low pressure area intensifying in the Cape Hatteras area early Sunday morning. Earlier in the week, the models showed the area far enough east that it was not going to affect the DC area. As the week has gone by, one of the models (GFS) has shifted this rain area west, and has it intensifying. Per the GFS, DC is now within the western edge of the precipitation. Another model (NAM) still shows the DC area rain-free. This is what causes weather forecasters to pull their hair out. The real pros have a handle on which model has been more accurate lately, and go with that. Other times, they hedge their bets and say maybe. Like everything in that business, it is all subject to change.
I think the mall at Tysons Corner has a covered walkway to and from the Metro Station. We may need it.