"Explanation: Normal cloud bottoms are flat. This is because moist warm air that rises and cools will condense 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 past summer."
"Researchers at The University of Auckland have reported a decreasing trend in average global cloud heights from 2000 to 2010, based on data gathered by the Multi-angle Imaging SpectroRadiometer (MISR) on NASA’s Terra satellite. The change over the ten-year span was 30 to 40 meters (about 100 to 130 feet), and was mostly due to fewer clouds at higher altitudes."
Photographer: Richard H. Hahn
"The photo above showing a phenomenal display of lenticular clouds was observed near Estes Park, Colorado on the evening of January 5, 2012. I was on the south side of Deer Mountain in Rocky Mountain National Park when the setting Sun lit up the western sky in shades of copper and tangerine. Lenticular clouds are a type of wave cloud that typically occur on the lee side of mountain ranges and form when air is forced upward as it moves over higher terrain. In winter, these clouds are often accompanied by downsloping winds ushering in warmer weather to the Front Range of the Rockies. The lack of snow in the foreground is evidence of prior downsloping and of the relatively warm, dry conditions that have prevailed in Colorado during the early winter. Photo taken at 5:02 p.m."
Estes Park, Colorado Coordinates: 40.372778, -105.519167
Photographer : Hector Fabian Garrido
"The photo above showing a sensational display of lenticular clouds was snapped near La Rioja, Argentina, at the base of the Andes Mountains, on September 9, 2011. I was doing seismic testing just after sunrise and was taken aback by the gold and tawny wave clouds that appeared across much of the sky. These lenticulars took shape to the lee (east) of the Andes, just west of my location -- the Sun was behind the camera. Lenticular clouds are generally orographic in origin, forming in lee waves when air is forced to rise over elevated terrain. On this early spring morning, the smooth structure of the waves, the illumination by the low Sun, and the absence of other types of clouds, gave the sky a surreal look."