Justin,
one guess is that when you ran a dry patch down the barrel after each shot, you were pushing fouling into the vent hole or vent liner. I can't remember from your build, did you install a Chamber's White Lightning touch hole liner?
If I read your post correctly, you were using your vent pick, is that right? it's possible that your vent pick was only cleaning out the small hole portion, but fouling was getting trapped in the cone portion of the vent.
Probably not the cold weather, but the problem could have been made worse by the humidity. it sounds like you were getting good fire in the pan, just not ignition, right?
That's my initial guess, based on your post.
Cheers,
Norm