© Stephen Burt
Stratfield Mortimer, near Reading, Berkshire RG7, United Kingdom of Great Britain and Northern Ireland
Latitude: 51° 22' 12'' N
Longitude: 1° 2' 24'' W
10 July 2010 2040 (Local Time)
Camera direction: towards NW
Image P/S code: P.4.12
Image I.D.: 5925
CL = 0, CM = 8, CH = 0
This is the leading edge of a double-layered band of invading Altocumulus that rapidly thickened and increased in amount.
The lower Altocumulus is dark grey (above the trees) and consists of cumuliform tufts with well-defined bases in most parts. To the left of these, the bases are dissipating and becoming ragged.
The higher layer is mid grey in colour and whitish in the thinnest parts. The elements in this layer are merging into long lines that seem to be converging toward a point near the horizon. This is the variety radiatus.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
A shallow, open-wave depression was developing over the west of the British Isles as this photograph was taken, in close proximity to another wave developing over eastern France.
Cirrus that preceded the Altocumulus can be seen to the east of Stratfield Mortimer, England, UK. The leading edge of the invading Altocumulus is about 50 km to the west.
The lower part of the picture shows many cigar-shaped Altocumulus patches, with on the whole fibrous, but not silky, extremities. The wavy band (1 - 2), brilliantly lit from the side, shows superimposed layers, four of which are clearly distinguishable at 3, and it has a flat, horizontal and greyish base. Similar clouds were seen at the same time at Tours and Rennes, 200 and 300 km from the place of observation. A weak Atlantic depression extended from Cape Finisterre to Cornwall and a strong upper current from the south-west was crossing the Pyrenees. There was strong instability, with thunderstorms over southern and western France.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
This layer of Altocumulus is clearly translucent (variety translucidus). Numerous intervals between the elements 1 and 2 also permit the sky to be seen (variety perlucidus). The presence of elongated elements, almost parallel to one another at 3 and 4, indicates the variety undulatus; there is also a banded structure (variety radiatus) across the picture at 5, 6, 7 and 8. The layer was rapidly invading the sky; in the direction in which the picture was taken, there is still an opening at 9. The station was in a maritime polar warm-air mass, about 100 km ahead of a cold front moving W-E which produced scattered thunderstorms at the end of the morning and later. The winds were SW-WSW up to 6 km.
Links in the image description will highlight features on the image. Mouse over the features for more detail.