Really interesting to hear the derecho talk this morning...in looking at radar around 6:30 p.m. last night (and I could kick myself for not grabbing a screencap), there appeared to be a prominent bow echo, with the leading edge bearing down on the Alexandria/Belle Haven area, then bending back over the District to the north and PWCo to the south. Some excellent pics of shelf clouds associated with last evening's derecho or near-derecho, too, on Twitter today.