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Clouds that resemble a succession of ocean waves breaking on the shore are known as fluctus. These can form at the boundary between layers of air moving at different speeds. This difference in wind speeds (or directions, for that matter) across a range of altitudes is known as wind shear. Typically, the upper air is moving faster than the lower. Strong wind shear can sculpt the clouds into a series of undulations, and sometimes the conditions are right for the wind to whip over the tops of these undulations into the characteristic curls that are the defining feature of fluctus. The effect is fleeting, lasting only a matter of minutes. Any cloudspotter who spots a fluctus is a lucky cloudspotter – like David Kent, husband of Lisa Kent (Member 54,274), who saw these Cirrus fluctus over Buffalo Mountain near Silverthorne, Colorado, US. Many think of these cloud features as like a roiling sea, but Lisa instead saw ‘mountains upon mountains’ – as if the ice-crystal clouds paid homage to the snowy peaks below.