Mammatus Clouds Over Saskatchewan

via NASA
"Explanation: Why is this cloud so bubbly? Normally, cloud bottoms are flat. The flatness is caused by moist warm air that rises and cools and so condenses into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms. Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate. Such pockets may occur in turbulent air near a thunderstorm. Resulting mammatus clouds can appear especially dramatic if sunlit from the side. These mammatus clouds were photographed over Regina, Saskatchewan, Canada during the summer of 2012."

3 Strange-Looking Kinds of Clouds

Supercell Time-Lapse

Noctilucent Clouds and Aurora Borealis

Published on Aug 11, 2013 "Displays of Noctilucent Clouds and Aurora during one night are rare. Noctilucent Clouds, NLC's for short, (aka Night Shining Clouds or Polar Mesospheric Clouds) are the world's highest types of cloud forming on the edge of space at height of about 80 km (50 miles) which is also height where auroras occur. Unlike most of other clouds types, which are mostly made of water vapour, NLCs are comprised of extremely small ice crystals. They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. They can be observed in the summer months at latitudes between 50° and 70° north and south of the equator."