© Frank Le Blancq
St Brelade, Jersey
Latitude: 49° 10' 22'' N
Longitude: 2° 10' 22'' W
15 July 2015 1853 (Local Time)
Camera direction: towards SSE
Image P/S code: P.7.2
Image I.D.: 5699
CL = 5, CM = /, CH = /
The photograph shows a long, low, tube-shaped horizontal cloud, which was approximately twice as long as the part shown in this image. Technically, it is of the genus Stratocumulus. As it is in the form of a roll and detached from any other cloud, it is an example of the species volutus. The cloud was first spotted at 1825 hours local time in a well-developed state and was still visible 45 minutes later with little change in appearance; however, neither its formation nor its dissipation was seen. The origin of this roll cloud is unknown, but sea fog was reported in the vicinity.
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The surface chart for 1800 UTC shows a shallow wave depression of 1 017 hPa over northern Germany. Very weak fronts link it to a shallow summer low of 1 012 hPa centred over the East Atlantic. At the time of the image, a light north to north-east wind of 5 kt was blowing over the Brittany, France coast near the image location.
The most representative sounding from Brest, France (WMO 07110), taken a few hours after the photograph, shows moist layers in the boundary layer extending to about 830 hPa. The surface wind is light from the east-north-east.
The photograph shows a roll cloud. It is a long, low, tube-shaped cloud, only part of which can be seen in this image. It has slightly ragged edges. Technically, it is the genus Stratocumulus; as it is in the form of a roll and detached from any other cloud, it is typical of the species volutus.
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This panorama image shows an approaching roll cloud. It is in the form of an extensive low, tube-shaped cloud mass (1, 2, 3), which belongs to the genus Stratocumulus. It has a fairly uniform colour that is lighter grey than the background cloud on account of its being completely detached, which is a distinguishing feature of the species volutus (unlike arcus, which is attached to another cloud).
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The outstanding feature of this photograph is a dark grey, banded mass of Stratocumulus cloud. The cloud as a whole is not attached to surrounding clouds and is thus designated as being of the species volutus. Volutus should not be confused with the supplementary feature arcus, which is attached to the front lower part of certain clouds. Volutus is typically a low, horizontal, detached, tube-shaped cloud mass, often appearing to roll slowly about a horizontal axis. In this instance, the roll cloud has a banded appearance which is unusual. It formed during thunderstorm activity, probably resulting from a combination of particular downdraught and humid conditions. The background cloud is Cumulonimbus, with the supplementary feature praecipitatio visible in the distance.
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