Like strokes from an artist's brush, the sky over Lake Superior and Lake Michigan was painted with long rows of white clouds on February 5, 2007. Called cloud streets, these clouds occur when frigid, dry air blows across the lake, where it picks up water vapor from the warmer lake. The water vapor freezes into ice crystals, and clouds form. The clouds take the shape of the wind as it gusts over the water. The same process can also cause lake effect snow or rain when the cold, moist air blows ashore on the lee side of the lake. Signs of lake effect snow can be seen along the southern shore of Lake Superior, which is bright white with little sign of brown vegetation poking through.