© Jüri Kamenik
Pääsküla, Tallinn, Estonia
Latitude: 59° 21' 37'' N
Longitude: 24° 37' 57'' E
01 August 2012 1938 (Local Time)
Camera direction: towards SE
Image P/S code: P.10.1
Image I.D.: 5042
CL = 3, CM = 0, CH = 1
Cumulonimbus clouds are heavy, dense clouds of considerable vertical extent, in the form of a mountain or huge towers. At least part of the upper portion is usually smooth, fibrous or striated and is nearly always flattened. The cloud base is often very dark. In this image, the sproutings of the upper part have become rather indistinct and flattened at 2 and 3, which is characteristic of the species calvus. Between the main towers, the cloud is still developing, having sharper outlines and a cauliflower appearance that identify it as Cumulus congestus. The supplementary feature praecipitatio, in the form of a shower, is falling from the cloud on the left. Higher in the sky, the fibrous elements of Cirrus fibratus can be seen.
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A deep low of 978 hPa was centred in the North Atlantic to the west of Scotland, UK. A slowly intensifying anticyclone of 1 021 hPa was centred over the Baltic states.
On the sounding from Tallinn, Estonia (WMO 26038), taken about 17 hours before the photograph, and on another taken several hours later (not shown), the atmosphere was unstable to daytime temperatures.
The 1930 hours (local time) radar image shows precipitation echoes to the south-west and south-east of Tallinn, Estonia. The echo to the south-east corresponds with the Cumulonimbus clouds viewed in the photograph.
A tropical depression over the northern part of the South China Sea intensified into a tropical storm named Mirinae. In Hong Kong (China), the weather was hot with sunny periods during the day and there were also a few squally showers and thunderstorms.
Thunderstorms are associated with Cumulonimbus clouds and are most often accompanied by precipitation. This photograph shows a thunderstorm during the evening from a Cumulonimbus calvus cloud. A thunderstorm is defined as one or more sudden electrical discharges, manifested by a flash of light (lightning) and a sharp or rumbling sound (thunder).
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This image permits comparison between the developing Cumulus congestus in the foreground and a recently transitioned Cumulonimbus calvus cell in the background.
The Cumulus congestus are strongly sprouting, generally have sharp outlines and are of great vertical extent. In comparison, the Cumulonimbus is of far greater vertical extent; however, this alone is not a deciding factor in identifying the cloud. The upper parts of the Cumulonimbus calvus are merging into a whitish mass with a domed top that has the suggestion of less-than-sharp outlines.
This is evidence that water droplets in the upper parts of this cloud have started to freeze, denoting the transition from Cumulus to Cumulonimbus. Once started, the transition from water to ice is a very rapid process: the Cumulonimbus will only retain the visible features of calvus for a few short minutes.
The diffuse appearance of the mid parts of the calvus is not due to freezing of water; rather, it is due to falling rain. Some patches of Altocumulus are in the foreground of the calvus and at the top right.
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This line of cumuliform cells is identified as Cumulonimbus as some of the upper parts have an indistinct whitish mass without sharp outlines (species calvus) and others are developing a fibrous and striated structure (species capillatus). The coding is CL = 9 due to the presence of this capillatus.
There is the appearance of a developing chaotic sky in this image. Broken sheets of ill-defined middle-level cloud combine with a diversity of clouds belonging to the low and high levels, giving a chaotic, heavy and stagnant appearance (CM = 9).
Hong Kong Airport, Hong Kong (China) reported a thunderstorm with rain at 1400 hours local time.
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In this photo showing active convection, the typical sproutings of Cumulus cloud can be seen. On the right of the upper portions of the cloud, there are cauliflower-like sproutings typical of Cumulus congestus. On the left, the upper parts are becoming more or less indistinct and flattening to resemble a whitish mass without sharp outlines as they transition into Cumulonimbus calvus. There are no striated or fibrous parts and no precipitation is visible, but a small pileus cloud indicates rapid growth of the cloud.
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A bank of Cumulonimbus calvus towers has become flattened at 1, 2, 3, 4 and 5 after losing their rounded tops. The coding is therefore CL = 3. A line of thin Altocumulus at 6 is also apparent. A number of Cumulus lie along the main cloud bank and the bases of many others are visible beyond the base of the principal clouds.
A cold-front system connected to a complex depression north and west of Scotland had crossed the area in the early hours of the morning. Large Cumulonimbi and showers built rapidly behind the fronts in the deep cold air. At the time of this picture, however, the Cumulonimbus development had become less active.
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Explosively growing towers at 1 and 2 are feeding this severe thunderstorm along the dry line in western Oklahoma. Some tower tops curl around toward the back of the storm and descend. The base of the SW portion of the storm is laminar, and is indicative of forced, stable, upward motion. This supercell storm moved northeast and produced large hail and a mesocyclone. The environment of the storm was characterized by strong vertical shear and a steep lapse rate.
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