On a tranquil summer evening, just as the sun dips below the horizon and darkness begins to settle, an ethereal spectacle ...

But its distinct water-like waves makes it a favorite among ... fluctus clouds are more likely to appear around sunrise or sunset, which is when lower clouds are cool and upper clouds are warm.

Lisa Covey traveled to Newfoundland earlier this summer and caught this unique photo around sunset in Rocky Harbour. There is the presence of some cumulus clouds ... of gravity waves or ripples ...

Noctilucent clouds on Earth are something quite spectacular, thin structures so high that they can still catch sunlight long after sunset ... be played by gravity waves, vertical waves moving ...

At the time those clouds appeared Tuesday, strong low pressure was developing over the Plains. It was swinging a cold front east, causing waves of rain and isolated thunderstorms across the Midwest.