Stripy clouds over Wigton

 I spotted this stripy sky over Wigton this morning - the sort of cloud formation that made me do a lot thinking in the summer. Then I remembered an experiment from the old Nuffield Physics A Level course. Stick a knife blade high up under the narrow flow from a tap and you get a stripy pattern too.

For the tap, it is a stationary wave. At least that's what the book says. For a stationary wave, an incident wave hits an obstacle and bounces back. The incident and reflected waves interfere. Not quite sure where the wave is originally because it's just a column of water. Anyway, it occurred to me that with the clouds, one moving air mass could be hitting another more stationary air mass to replicate the knife scenario...?