Sunset from the Potomac
One of my favorite things about living in DC is that the seasons all get their proper time. In Utah, winter seemed to last six months or more with all the snow and spring and fall only lasting a couple weeks. In Texas, it went from hot and summery to gray and dreary and barren trees without snow to make it worth it. It was rarely cold, but it was certainly bleak.
Here, the seasons take their time and I get to fully enjoy them. Or, in the case of winter, know that they will end. I'm fine with winter and snow, but I don't love being cold.
Fall loses a few points in the race for favorite season because it is the harbinger of winter, but gains points because it is so lovely here with all the foliage.
This year, and I've heard this from a few sources as well as my own observations, has been particularly gorgeous and the leaves and weather are taking their sweet time to change.