Appearance in Satellite Data

  • The satellite image shows a meso- to synoptic scale cloud field of multilayered cloudiness mostly with a sharp edge along the cyclonic side.
  • There is a typical relationship between this cloud field and the upstream frontal system: the cloud field of the Detached Warm Front can be found separated and downstream from the cloudiness of a classical frontal system.
  • Height and thickness contours accompany these configurations with pronounced ridges bound by zones with strong gradients of the isolines (see Key parameters); the Detached Warm Front cloudiness can be found in the eastern downstream branch.
  • In the VIS image the cloud field of the Detached Warm Front is white, indicating lower multilayered cloudiness.
  • In the IR image the grey shades vary typically between light grey and grey; high pixel values can mostly be found at the cold side of the thickness gradient (leading area of the frontal cloudiness).
  • The WV image shows a wide broad anticyclonic curved area with high WV pixel values, indicating high moisture content within the gradient zones surrounding the equivalent thickness ridge.
  • A typical area for the occurrence of Detached Warm Fronts is the windward side of the Alps, being accompanied by increased weather activity (see Weather events):
    if the Detached Warm Front moves against mountains (for instance in central Europe against the Alps), enhanced cloudiness, Barrage Cloudiness, can be found at the windward side (see Barrage Cloud ), as well as high Lee Cloudiness at the lee side (see Lee Cloudiness ).
  • Some features of a life cycle can be observed:
    • Often the cloudiness of the Detached Warm Front moves downstream from a classical Warm Front system and becomes an independent system.
    • It mostly propagates southward, leading to a movement against the Alps in central Europe.
    • In the case of a Detached Warm Front on the windward side of the Alps a typical feature can be observed if the whole ridge system moves eastward. In this case, that part of the high cloudiness of the Detached Warm Front reaching the eastern edge of the Alps propagates quickly southward while the rest of the cloudiness is still bounded by the mountain chain.
    • During its lifetime high level cloudiness often dissolves so that IR grey shades become darker.

04 January 2005/00.00 UTC - Meteosat 8 IR 10.8 image
04 January 2005/00.00 UTC - Meteosat 8 WV6.2 image

The satellite image at 00.00 UTC shows the cloud band of a Cold Front, from the Azores across Ireland and Scotland where it changes over to the cloud shield of a Warm Front over south-western Norway. Downstream, from Sweden southward as far as Austria, the satellite image shows a grey cloud field of a Detached Warm Front, which is already separated from the Warm Front Shield. North of the Alps Barrage Cloud can be recognised as the mountain forms a natural barrier. A little to the east of the Alps in Slovenia the clouds seem to penetrate southward.

The IR image shows bright grey shades indicative of the initial stage of the life cycle, with the brightest grey shades in the centre and at the leading edge which is nearly in accordance with the description of the ideal situation. The sudden decrease of the pixel values along the leading edge fits with the superimposed jet at approximately 300 hPa. The boundary of white to dark grey characterizes the jet axis.

In the WV image the separation between WF shield and Detached Warm Front can be clearly seen. Greyer value pixels are all located over southern Norway, Denmark and eastern Germany. An interesting and dominant feature in the WV image is the black, dry stripe from central Sweden over the Baltic Sea into the Baltic States and then further south into Serbia. It is an indication of the anticyclonic circulation within an upper level ridge.

04 January 2005/12.00 UTC - Meteosat 8 IR 10.8 image
04 January 2005/12.00 UTC - Meteosat 8 WV 6.2 image
04 January 2005/12.00 UTC - MSG VIS 0.6 image

The whole system has moved rather north-east and the detached cloudiness moved south. As the Detached Warm Front is influenced by the orography of the Alps, intensive cloudiness on the windward side and high Lee Cloudiness on the lee side (south-east Austria) develops.

In the WV image the detached cloudiness is seen as grey indicating less moisture. The WV dark stripe on the anticyclonic side is still very much noticeable.

The IR loop shows the development of the Detached Warm Front. Special attention should be paid at the time when the Detached Warm Front hits the Alps. As it then wanders eastward, more cloudiness penetrates southward on the eastern edge of the Alps over Slovenia.

Loop: 03 January 18.00 - 04 January 18.00 UTC, Meteosat 8 IR 10.8 hourly images