During the full moon.
This must have something to do with gravitational pull, the tides, dim comets in the sky, magnitude of the moon, or the amount of frustration of Seattle deep sky observers?
Again, the theory comes true.
Clear skies (Seattle) = [Sky] - [Clouds] + [Full moon] + [maximum natural light pollution]
Clear Sky Chart:
Full: March 10
Yep. Just another night indoors watching Netflix movies....