This picture will need expanding to see the detail. It had all but disappeared by the time I was able to stop safely for the photograph. The main bit of the lenticular is middle left but to the right of this there is the trace of the top of a wave shape - just the upper whisp of the lens shape. Maybe here we have to "loops" of a stationary wave, as I call them in class. Putting the two together gives a full wavelength. Sadly, there is nothing to measure the scale against. There is no knowing how far away the clouds are.
