This form of prefrontal convergence is also clearly connected to the diurnal cycle as night sets in, most of the cells dissolve. By that time the convection embedded within the approaching cold front is dominant and a large MCS covering Poland is observed in the end of the case study.
The severe convection RGB showed the physical contents of the cells as the different colours easily tell whether the cell are consistant of large ice particle or small ice particles. This discrimination makes it easier to tell if cells would further develop or if the mature stage is already reached and/or cells are already dissolving.
As convection is a small scale phenomenon the use of Limited Area Models (LAM) is beneficiary as it can explain and reveal the upward motion and the convergence near the surface explaining the rise of the airparcel in order to reach their level of free convection. The analysis of the Austrian LAM model (Aladin) revealed this converging motions at 925 hPa and the divergence (e.g. outflow of air near the cloudtop) at 700 hPa. The windvectors near the surface also showed this converging movement and perfectly aligned the orientation of the prefrontal convergence line at an early stage of development.
The instability associated to the convection was pictured using the Showalter index derived from ECMWF. Values under 0 and occasionally under -3 depicted the whole area of the leading edge ahead of the front. A release of latent instability by the strong surface heating, that attributes to the thunderstorms development. As the convection set in it was observed that the cells developed in a tongue of ThetaE 850 indicative for the prefrontal upward motion branch where the convection develops.
As a nowcasting tool the use of EUMETSATs GII (Global Instability Index) proved to be usefull. At already an early stage this product depicted the orientation and location of the prefrontal convergence line. There was however some false alarm inferred as also Croatia was depicted as being unstable and convection was expected. A further analysis of the radio sounding however in the Physical backgound showed that the K-index values were correct but that convective development was seriously hampered by a strong capped inversion that day.