The top of this cloud is 150 metres above the plain. Soaring pilots call these clouds “Lennies”. Usually, they occur kilometres above the ground, where they are Altocumulus lenticularis (Acl). They form when the air-flow rises and cools below the dew point. Warmer air above the cloud stops the lower air from rising any higher, creating a smooth surface by laminar flow. Other clouds below this lennie show turbulent air-flow. At sunrise that day (6/7/15), the temperature was +0.6° and the dew point 2.1° lower. Fog filled the valley, but it had cleared when the photo was taken 45 minutes later. The view is towards 280°; surface wind 010°/4 knots; 1500-metre wind 295°/ 22 knots.