The answer to all of the above is...YES
Just kidding, but all of the items you listed could be a factor. From what I've been able to gather from the fishing reports, etc...while things are on the verge of busting out, it hasn't happened yet. In the meantime, we're getting fronts moving through every few days, and the weather has been fairly unsettled. Down here, it was very windy today, and I think it was the same up there...unsettled weather, unsettled fish, which can make for some tough fishing.
I would suggest picking up a thermometer...it can really tell you the whole story at a glance. If it is around 50, or above, you can probably expect some action on dries. Below that mark, the fish probably won't look up, even if a hatch is in full swing. I remember two weekends last April - the first one, we came up, the weather was very unsettled, and the water was still a bit chilly - all the action was subsurface. The next weekend was sunny and calm, and I couldn't help but get a strike on a dry in every pool.
Nymph fishing can be tough - a lot of the time, even with an indicator, you can't see the strike. Sometimes, you just feel "something" on the line, and sure enough, it's a fish. Other times, you actually have to see the fish make a dash for your nymph to get him.
Finally, whether you're fishing a nymph or a dry, you have to present the fly in a likely feeding station in a given pool, drifting in a natural manner with the current. Drag is a killer. Keep your casts short - in fact, in a lot of cases, I'm just flipping out the leader, with only a little bit of line hanging off the end. Keep low, wear subdued colors, and try not to cast a shadow over the pool. Work the "edges", where the fast water meets the slower moving water, and pay particular attention to the tail ends of pools, and, in the front section of the pool, a corner of calmer water off to the side of the main flow. Try to keep as much of the leader off the water as possible, and follow the drift of the fly with your rod. Finally, if you aren't already doing so, make sure you wear a pair of polarized sunglasses...it's amazing what you miss in the surface glare without them.