Author
Jarno Schipper - ZAMG
Introduction
This small case study describes a Genoa low which moved along the '5b-cyclone path'. As the system was passing over the Eastern part of the Alps a Comma cloud detached from the occluded cloudband. Under the influence of a pronounced PVA maximum the Comma intensified, causing heavy snowfall and chaos in parts of Austria, Slovakia and Hungary.
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| Snow causes chaos on the streets of Vienna. Copyright © ORF |
The case study will present a compilation of meteorological data and charts, describing the events that triggered the large snowfall. The mini case study is further supplemented with a chapter called "Interactive overlays". In this chapter you can overlay various numerical parameter fields on the corresponding satellite imagery. Through this interactive approach you can reconstruct the case and exercise with it. If you think you can contribute to this Case study or to EUMeTrain, by providing us dates of interesting cases which happened in your region of interest, we encourage you to write us using the above e-mail address.
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| Meteosat 8 Airmass RGB - 27 January 2005, 05 UTC - The depression is already located over Eastern Europe. From the cloudband a Comma cloud just detached. |
Synoptic situation
A Genoa low is a low-pressure system developing south of the Alps in the Gulf of Genoa and northern Adriatic Sea. Genoa cyclones usually remain stationary (or at least leave a residual trough) south of the Alps throughout their life history. If the lows do move, they generally follow one of two tracks (source weatheronline):- The first track has a northeasterly to north-northeasterly direction across the Alps. This track is also known as the '5b-path', often bringing extensive rainfall and catastrophic flooding to Austria, Germany, the Czech republic and Poland, as the one in Summer 2002 (see Flood Catastrophe Central Europe).
- The second track, associated with a strong anticyclone over the Balkans, Turkey and the Black Sea, has a southeasterly direction from the Gulf of Genoa towards the Ionian Sea. In this case, a gale force Bora along the Croatian Adriatic coast is extremely likely by the time the depression moves into the Ionian Sea.
The surface analysis chart of January 25th 2005 is given below. On the map the Genoa low is situated over the Mid Mediterranean and the Adriatic Sea. At this stage the cyclonic movement already directs moist air from the Adriatic into the Alpine region causing snowfall in northern Austria. Forming of this depression as well as its movement will be followed and discussed by means of the satellite images.
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Synoptic chart - 25 January 2005, 06UTC |
The cyclone described in this case follows the 5b-path, which is described above. It moves over the Alps and, while slowly moving further northwards, it dissolves. Due to the cyclonic movement moist air from the Adriatic is transported into the Alpine region. The lifting of this moist air causes substantial snowfall on the northern side of the Alps. In the second phase of the development a Comma cloud detaches from the frontal system. Under the influence of a PVA maximum it enhances and causes locally even more snow.
IR Imagery (Meteosat 8 channel 10.8): time sequence
This chapter shows and briefly describes the development in a sequence of hourly infra-red images.
WV Imagery (Meteosat 8 channel 6.2): time sequence
In this chapter the cloud configurations can be better related to the upper level dynamics using Meteosat 8 - WV6.2 channel.
Meteosat 8 - Airmass RGB: time sequence
The development and especially the physical background is pictured using the sequence of hourly Airmass-RGB images.