Thin, wispy cirrus clouds form at high levels so they are made of ice crystals that can fall or be carried with the strong winds at these levels, creating a variety of interesting shapes in these clouds. This example from Seattle Washington shows an example of the subspecies Cirrus fibratus (named for their fibrous appearance). They covered the sky so much on that day that I had to take a horizon-to-horizon panoramic photo to try to fully capture the extent of these clouds that were oriented in lines along the upper-level wind.
Location: Seattle, Washington
Date: June 2013