MSG IR 10.8 with surface pressure and geopotential 300 hPa: time sequence

18th August 2004: 06UTC
6h-forecasts of surface pressure (blue) and geopotential 300 hPa (red) of the DWD’s GME-model and the corresponding IR-image are displayed. The relevant area (Western France and the Bay of Biscay) lay under a trough and weak cold air advection. East of that area there was weak warm air advection. The vertex of the wave-formed cloud is near the change of the sign of thermal advection. The surface pressure does not yet exhibit the typical structure of a developing squall line.

18th August 2004: 12UTC
The satellite image shows, over Western France, two short wave troughs and the typical decrease of surface pressure with negligible horizontal gradient („thunderstorm-sack“). We recognise a chain of deep convective cloud east of 0° longitude. Over western Germany we see weak warm air advection and over the compact cloud area negligible thermal advection (see radio-soundings).

18th August 2004: 18UTC
The axis of the upper air trough has arrived over the French Atlantic Coast. Near Paris and over Germany we can see a clear diffluent flow super-imposed on the high clouds of the squall line. An area of relative low surface pressure developed in this region.

19th August 2004: 00UTC
On the 300 hPa we find two short wave troughs (Northern France / Belgium and Northern Germany) The first one has triggered convection over Eastern France. The second one the cloud area from North Germany to South Scandinavia. The two short wave troughs are related to two areas with relatively low surface pressure. From north Germany to Scandinavia warm air advection and stabilisation is taking place.