How do you tell that they are notilucent clouds and not regular clouds?
They shine like the ones in the picture in this article and they are in the northern sky, well above our altitude. They are wispy as in the pic and they do not seem to move in the windscreen as a regular cloud formation would as you fly along. I had them in view for hours.
Oh you can tell they are noctilucents. They are up about 50 miles which is far higher than the highest convection clouds go. Well before sunrise they’ll show up and have this amazing glow to them. I saw them over Seattle a couple of years ago. Pretty kewl!