My best guess is that this is a female junco (captured from our back entry through the glass of our back door). It's doubtless in the Slate-colored race (population)--the only one regularly in the east. But its appearance is a bit odd, and my ornithologist emailer is not sure, thinking it could be a hybrid. There were several juncos around (clearly identifiable with white at the corner of their tails in flight), but I saw this bird only very briefly and not in flight. Grey and cloudy today, finally with some rain.