Cirrocumulus sky over Missouri

The photo above, captured about an hour before sunset at our home in west-central Missouri, shows a “mackerel sky” composed of cirrocumulus undulatus clouds. Photographers Ramona Miller, Grant Miller

The rippling is a result of upper atmospheric waves. Cirrocumulus clouds form at altitudes above about 15,000 feet (4,572 m). They’re composed of ice crystals and, as with most wave clouds, are oriented roughly perpendicular to the direction of the wind.

This sort of sky is often indicative of an approaching front; a warm front ahead of a storm system. On this evening the National Weather Service forecast 100 percent chance of rain for our location the next day — the forecast held. Photo taken on February 14, 2012.