Arcus clouds


This is a rather typical shelf cloud …

Shelf cloud on a night time thunderstorm over the northern Adriatic sea, approaching Koper, Slovenia. The cyan line denotes the upper edge of the shelf cloud. The shelf cloud reaches about 1/4 to 1/3 of the way from the cloud base to the surface. Note the precipitation in the background, illuminated by lightning. Outflow is marked with blue arrows. Photo: Jure Atanackov.