yep - that's the only way NYC cools off at night in the winter. Otherwise you get like 5-6 degree diurnal temperature variation lol. DCA is similar but it's not quite as profound. NYC is nuts. Without a fresh fetch of cold air coming down the Hudson your low is maybe a degree or two off from the temp at, say, 5pm. Often times it goes up a couple of degrees between 2am and sunrise.