Last Wednesday (22 November) at dusk, crows were flying in the thousands near the North Bethesda (formerly White Flint) Metro stop; some were in trees, many were in the air, and many were arriving in massive flocks. They were in trees (including street trees, and in the scrubby / small tree area just east of the Metro station) over to Citadel Avenue to the east, Marinelli Road to the south, and Old Georgetown Road to the north (and the Metro station to the west). They weren’t anywhere else (except flying in). They weren’t in the scrubby / wooded area east of Nebel Street.
At about 7PM, they were still there, mostly in the trees (a few were still flying), and generally in the crowns (not throughout the canopy, but towards the very top). They were in a very tightly delimited area, and only at high densities (i.e., they were not in sparsely populated crowds, but only densely, with each individual maybe less than a couple feet from another). They were in street trees along Marinelli Road.
This phenomenon is studied in Lawrence, MA: https://www.wintercrowroost.com/
Notes on Winter Crow Life in the Delaware Valley; Witmer Stone; The Auk, Vol. 20, No. 3 (Jul., 1903), pp. 267-271 https://www.jstor.org/stable/pdf/4069789.pdf
California central coast: “You can see large flocks from late summer until about February as they loudly gather to search fields for food.
Experts say during that time, the roost breaks up into smaller flocks to feed in the morning and by afternoon join each other in the sky as they make their way back home.
The Morro Coast Audubon Society says the reason crows seem to “disappear” in the spring in summer is because they pair up in breeding territories rather than flock together in big groups.” https://www.ksby.com/news/local-news/why-so-many-crows-experts-say-they-are-roosting-in-five-cities-neighborhoods
Kinglets in the cold, Bernd Heinrich: https://vtecostudies.org/blog/kinglets-in-the-cold/
Flora and Fauna of Washington, DC and environs 