The wind changes whenever someone in HTC feels like it.
And currently there are layers from 0-10,000 10,000-20k and 20k+
I'm only talking about the surface layer (kinda important for landing).
And even easier way to find the wind direction is to take a c47 with 25% fuel, roll her up to about 40 mph, then let go of the rudder. It will "weathervane" immediately.