How they form Found more than 20,000 feet high, these curly, wispy clouds consist of ice crystals and can form in any season. Cirrus generally appear white but, at dawn and dusk, can take on a rainbow of colors.
What to expect Fair weather
Warning signs Don’t confuse cirrus clouds with other high-altitude clouds such as cirrostratus clouds or high, lumpy cirrocumulus clouds. The former signal a good chance of rain or snow within 24 hours, and the latter often indicate cold weather; in the tropics, however, cirrocumulus clouds might mark a hurricane’s approach.
What to do Milk the weather window: Enjoy a long lunch or tack on another objective.