Hans-Dietrich Widmaier spotted this volutus cloud spanning the horizon over Munich, Germany. Volutus is a species of cloud that appears as a long roll and tends to appear low enough to be classed as a form of Stratocumulus – the low, solid-looking cloud of extended heaps or rolls. Volutus is known colloquially as a roll cloud.

These clouds appear detached from any surrounding formations, sometimes developing in the gusting winds of cold air that spread out ahead of storm systems. Indeed, the dark clouds in the distance beyond this volutus suggest a storm brewing on the horizon. A volutus cloud can move at a fast clip, rolling along at speeds of up to 35 mph (55 km/h) and rotating as it travels. The rotating movement is unlike that of an actual tube rolling along ground. Instead of rotating in a forward motion, volutus clouds appear to roll against their direction of travel, lifting at the front of the tube and dipping down at the back.

Cloudspotters with a liking for pastries might consider this long, rolling vortex of a cloud to resemble a strudel – covered perhaps with a generous sprinkling of powdered sugar. This sounds about right, especially since the name strudel is the German word for a ‘vortex’, ‘whirl’, or ‘eddy’.