What is true of high clouds they are?

High clouds, typically found above 20,000 feet, are primarily composed of ice crystals due to the cold temperatures at these altitudes. They include types such as cirrus, cirrostratus, and cirrocumulus. These clouds are generally thin and wispy, allowing for sunlight to pass through, often creating halo effects around the sun or moon. High clouds usually indicate fair weather, but they can also signal an approaching storm when they thicken and lower.