© 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 I.D.: P.7.2
CL = 5, CM = /, CH = /
Links in the image description will highlight features on the image. Mouse over the features for more detail.
The photograph shows a long, low, tube-shaped horizontal cloud, which was approximately twice as long as shown in this image. Technically it is 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 18.25pm in a well-developed state and was still visible 45 minutes later with little change in appearance, but neither the formation nor dissipation were seen. The origin of this roll cloud is unknown, but sea fog was reported in the vicinity.
The surface chart for 1800 UTC shows a shallow wave depression of 1017 hPa over northern Germany. Very weak fronts link it to a shallow summer low of 1012 hPa centred in the east Atlantic. At the time of the image a light north to northeast wind of 5 knots was blowing over the Brittany coast near the image location.
The most representative sounding from Brest (WMO 07110) a few hours after the photograph, shows moist layers in the boundary layer extending to about 830 hPa. The surface wind is light from east-northeast.
The photograph shows a roll cloud. It is a long, low, tube-shape 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.
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 and lighter grey colour than the background cloud on account of being completely detached, which is a distinguishing feature of the species volutus, (unlike arcus which is attached to other cloud).
The outstanding feature of this photograph is a dark grey banded mass of Stratocumulus cloud. The cloud as a whole was not attached to surrounding clouds and is thus designated as species volutus. It should not be confused with 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 supplementary feature praecipitatio visible in the distance.