In the immediate Washington, DC region, the driest area extends from the northern Shenandoah Valley eastward through northern Virginia, the District of Columbia, and southern Maryland, where most places have seen only 50-75% of average precipitation over the last 90 days.
Through this morning, here are the year-to-date precipitation totals and departures from average for the Nation's Capital area:
Washington National: 9.11"/-20%Images (click to enlarge): 90-day percentage of normal precipitation from NWS, Washington DC precipitation vs. average from Climate Prediction Center
Washington Dulles: 9.19"/-21%
Baltimore (BWI): 10.77"/-14%