English: n the early morning hours of sol 99, Phoenix used its lidar (a skyward-pointing green laser beam) to search for clouds. The beam detected clouds at elevations between 3.5 and 4 kilometers above the surface. As the observation continued, it detected "fall streaks," where ice crystals that formed within the clouds began to descend toward the ground; as they descended, different wind speeds at different altitudes caused the sheets of falling snow crystals to shear out horizontally. When the lidar experiment quit operating at 05:21 local time, the crystals had fallen to an elevation of 2.5 kilometers, and probably fell further before they reached air that was dry enough to cause the crystals to sublimate back into a gas. Later in the season, the falling snow may survive all the way to the surface.