© Jarmo Koistinen

Savonlinna, Finland

Latitude: 62° 0' 0'' N

Longitude: 29° 0' 0'' E

19 July 2010 1247 (Local Time)
Camera direction: towards NW

Image P/S code: S.1.14

Image I.D.: 5498

C_L = 2, C_M = 3, C_H = 2

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  Cirrus castellanus and Altocumulus

  This image shows a solitary and dense Cirrus castellanus altocumulogenitus cloud that has developed from Altocumulus castellanus through the glaciation of the whole cloud. Therefore, the common base of the cloud is not quite horizontal, but contains short, virga-like protuberances. Due to the history of the cloud, it can be assumed that the altitude is unusually low for Cirrus. A thin layer of Cirrus fibratus is present closer to the observer. It is generated by the glaciation of the rear edge of the frontal Altocumulus stratiformis translucidus, present at the top of the image and wide in the sky behind and to the side of the observer but not visible in the image. The altitude of middle clouds measured by a ceilometer 30 km north-north-east of the photo location does not match the respective sounding temperatures very well. The Cumulus at levels of 450–800 m, according to the ceilometer, is mostly ragged Cumulus fractus, but some whitish clouds in the background are more compact and look like Cumulus mediocris.

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  © Jarmo Koistinen
  Savonlinna, Finland
  Latitude: 62° 0' 0'' N
  Longitude: 29° 0' 0'' E
  19 July 2010 1247 (Local Time)
  
  
  Camera direction: towards NW
  C_L = 2, C_M = 3, C_H = 2
  Image P/S code: S.1.14
  Image I.D.: 5498
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  Clouds in the image represent the rear edge of a slowly moving cold anafront. It is located approximately 100 km east-south-east from the image site and is moving further eastwards. Nimbostratus-type sky prevailed all morning and was followed by a gradually thinning layer of Altocumulus. There are signs of the formation of a young wave at the front (see the satellite image).
  © Deutscher Wetterdienst
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  The sounding was measured four hours before the cloud image was taken and 180 km west-north-west from the location. Confusingly, as regards the observed glaciation of the Altocumulus, a ceilometer 30 km north-north-east of the photo location measured the rear edge of a retreating middle-level cloud layer as being at an altitude of 2 900 m, whereas the freezing level in the sounding is at 3 500 m and the favourable temperature for glaciation (–10 °C) is at approximately 5 000 m. The sounding is very dry, indicating the post-frontal air mass.
  © University of Wyoming
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  The cloud band of the cold front is dominating in the NOAA-19 image (a combination of channels 1, 2 and 4), taken approximately 15 minutes before the cloud image. The cloud image location is approximately in the middle of the satellite image, at the rear of the frontal band. The bend in the cloud band suggests that a wave might be initiating.
  © Finnish Meteorological Institute