If you are a glutton for punishment and don't mind being cold, fly fishing in the Appalachian Mountains can be quite beautiful in the winter. Cascading streams lead to dramatic waterfalls covered with icicles. Rhododendrons and pines dot the surrounding forest, lending a rare spot of color to the grey landscape. You'll find nary a soul on most streams, especially if you steal a weekday.
You decided you'll put up with it and brave the elements, you might as well catch some fish while you're at it. Now I don't want to upset any traditionalists but in my experience their are not many fish that will take a dry fly in the wintertime. The reason, there aren't any real hatches in the wintertime. I enjoy fishing a dry fly as much as possible, but as much as I want fish all over my Quill Gordon in January it is not very likely to happen. The are several reasons for this, and why you'd be better off nymph fishing instead.
First of all, like the air, the water is cold. Of course trout like cold water, only warm water is a problem right? When it comes to them breathing yes, but when the water temperature gets below 40 degrees a trout starts to drastically slow down. Metabolism slows and the caloric needs of the fish decreases. That means that the fish is going to eat less food and less often. The chance that a fish is going to eat your dry fly, or any fly for that matter, is reduced during the wintertime.
Second, trout in particular are always in Math class. They have one equation that they solve over and over: is that bit of food worth my effort (or calories) to go get it? They have it hard wired into them and this is all they do all day, all the time. Unless they are spooked or mating, this is really the only thing that trout think about. If the fly is too far away from them, then they aren't coming to get it. In the winter trout are mainly sitting tight to the bottom and therefore you have to get the fly to them, they are likely eating in the same 1' water column along the bottom never looking toward the surface so they'll never even acknowledge your fly.
Lastly, the final argument I'll put forward about not using dry flies is that there are hardly any insects hatching in the winter. You can find hatch charts that cover the Appalachians, Virginia, or the East Coast and you will see something we call midges (a generic term for very small flies) and maybe little black caddis listed from November-February. So yes there are occasional hatches, but these flies are very small, which means usually not worth the effort that we discussed in the previous paragraph. Also, unless your sight is good, we are talking size #18-22 hooks. Those are roughly pinkie nail sized flies and tough to see in good conditions.
Now, of course there are exceptions to this rule and I am sure plenty of people will disagree, but this is my opinion and experience of three decades of fly fishing. If you are dead set to fish dries I will give this bit of advice for the best success:
-Fish after three nights of temperatures above freezing. This allows warmer temperatures to stabilize water temperatures and promote bug activity.
-Even though any hatches are small use bigger, drab colored dry flies. If the fish is going to swim up for it, it better be worth the calories.
-If you know how to, fish with a nymph dropper. A fish might be curious of your dry and end up eating either fly. You can double your chances and see if a particular fly is more successful than the other.
Also, spring creeks are a good idea if they are in the area. Here we can choose between Mossy and Beaver Creek near Harrisonburg, and Buffalo Creek outside of Lexington. Because of these springs the water temperatures remain higher than the other streams in the area. A good couple of warm days will provide more hatches than the cold flowing freestone streams. Or you can be like me and hibernate until March when its tolerable outside again.