A striking cloud over Boulder, Colorado: What is its altitude, and why does it matter?

Scientists from the NCAR Foothills Laboratory, US, made significant efforts to study a spectacular cloud layer identified as cirrocumulus that formed over Boulder, Colorado on March 23, 2011. Photographs revealed that the cloud layer was beautiful and intricate, with small elements throughout north-south waves that looked like rippled sand along the upwind edge and east-west striations near the middle and top of the photo. There were several clear 'holes', including one long east-west hole or 'moat' near the leading edge. Charles Knight, a researcher from the NCAR Foothills Laboratory thought the clouds consisted of supercooled water droplets, with holes and slots developing as the droplets were converted to ice crystals that fell in thin streams of virga. This behavior would put the cloud height at the lower moist layer at around 5,000 m, where the temperature was -19°C.