Stratocumulus is perhaps the most common of clouds in the British Isles. It is not flat enough to be proper stratus, and lacks enough vertical development to be cumulus. It is usually grey, but often white with grey lower parts. It occurs in patches, sheets or layers, composed of rounded masses and rolls. It is usually a low cloud but can occur at mid altitudes where it may be confused with altocumulus stratiformis, but can be differentiated by observing the larger size of its elements, which are generally larger than the width of four fingers held at arms length overhead.
It can occur in a variety of forms:
Other than stratus, this is one of the most unremarkable of clouds in ordinary light. The photo shows its occurence as a sheet towards the right, and as more separate masses towards the left. In the places where the sun could be vaguely seen through it, it would be described as Stratocumulus perlucidus and in those areas where it is thicker and grey enough to obscure the sun it is described as Stratocumulus opacus
Stratocumulus, Harriseahead, Staffordshire
28th June, 2011
© Lionel Burch
Sometimes it can be quite thick and result in gloomy conditions as is the case here, although it is rather more broken in the foreground.
When it is thick enough it can produce light drizzle, especially on windward coasts and over hilly areas, where it is forced to rise.
Stratocumulus opacus, Bamburgh, Northumberland
24th July, 2002
© Paul Swinhoe
Where it occurs as separate rolls it can create a beautiful effect when the sun is low, such as in this example which was taken from the slopes of Pey y Role Wen at the head of Nant Franccon at dawn on an autumn day. In this case a mild SW wind was blowing moist tropical maritime air from the sea over Snowdonia.
When it is thick enough it can produce light drizzle, especially on windward coasts and over hilly areas, where it is forced to rise.
Stratocumulus opacus, Snowdonia, North Wales
17th November, 2011
© Edward Swinhoe
Occasionally the weight of water droplets in the cloud is enough to produce mamma. On this day there were several thick sheets of Sratocumulus, some of which produced the odd spot of fine drizzle.
Stratocumulus opacus with mamma, Westport Lake, Stoke-on-Trent
31st July, 2018
© Paul Swinhoe
Taken on the same day as the example above, towards the edge of some of the sheets of stratocumulus there was clear evidence of wave motion, producing Stratocumulus undulatus. In this case the downward movement between the bands of cloud was enough to cause the cloud to evaporate, revealing blue sky between the rolls.
Stratocumulus undulatus, Westport Lake, Stoke-on-Trent
31st July, 2018
© Paul Swinhoe
Of course, there is no such classification as miserabilis, but perhaps there ought to be as it sums up many of the typical grey days we experience in the British Isles, particularly in the winter half of the year when a humid tropical maritime air mass behind a warm front dominates the situation. In the winter months, the sun is not usually powerful enough to burn off these clouds, but unfortunately we often have days like this in the summer as well especially in coastal areas with an onshore wind.
Stratocumulus opacus, Seaburn Beach, Sunderland
4th September, 2000
© Paul Swinhoe
On the other hand, if the cloud is thin plenty of light passes through and it can be perfectly pleasant. With perlucidus clouds the light of the sun is clearly visible but not its disc, but with translucidus even the disc of the sun can be seen through the cloud.
In this example the translucidus clouds appear mostly white with very little shading. They dominate the scene, but there are some darker perlucidus clouds near the left margin of the photograph.
Stratocumulus translucidus and perlucidus, Howick Bay, Northumberland
21st July, 2002
© Paul Swinhoe