18th August 2004: 06UTC
6h-forecasts of KO (blue) and Omega (red) of the DWD’s GME-model and the corresponding IR-image are displayed. Over the relevant area (Western France and the Bay of Biscay) we find both negative KO-values (dashed, i.e., potential instability) and upward motion (dashed). this indicates that the cloud area will intensify and convection will occur later on.
18th August 2004: 12UTC
The NWP-analyses (GME-run from 12 UTC) exhibits from Western France to the bay of Biscay deep convective clouds, superimposed by negative KO and Omega values, the latter in connection with a short wave trough. The triggering of convection continued.
18th August 2004: 18UTC
Most parts of the deep convective clouds are super-imposed by upward motion and negative KO. However, especially in the southern parts we can see intense dynamical forcings whereas further to the northeast we observe only small vertical motion.
19th August 2004: 00UTC
The centre of intense upward motion (in front of a short wave upper trough) in coincidence with negative KO shifted to northwest Germany and the North Sea. Over the Eastern part of the North Sea stratiform rain was observed and also lightning detected. No explanation can be retrieved for that from the NWP-fields of KO and Omega. However, from the corresponding radio-soundings KO-indices between -2 and 0 were derived, i.e. conditional instability.
