Steps up the Sky

Photographer: Becca Jones 
Summary Author: Becca Jones; Jim Foster

The photo above shows willowy waves of cirrocumulus or possibly altocumulus clouds that my kids love to call "steps up the sky." It was taken on April 20, 2009 from Bellingham, Washington. These clouds aren't actually stacked atop each other; rather they're widely spread across the sky at basically the same altitude. Perspective gives them this stair-step look. Such waves can be observed when air moving across elevated terrain begins to undulate. Water vapor in the rising air condenses as it cools until saturation occurs. Where this air stream ceases to rise and begins to sink, cloud droplets evaporate upon moving into drier and warmer air.