Introduction
The effect of the advection of dry air over Skagerrak and Kattegat towards Sont is clearly displayed in the VIS-SAT image of fig 2 and fig 4. Transported over the warmer seawater and a fetch of more then 200km off the Norwegian southeast coast convection starts into a remarkable cloudstreet or convergence line in general with a width of no more then 40km over the Sont, spreading downwind towards the Polish and German coast. At the entrance of the Sont convergence at lower levels triggers convection helping the CU-clouds from the cloudstreet to develop into the first CB-clouds. Convection is visible as well south of the Danish isles Fünen and Sealand in fig 4. After a much shorter fetch off the coast these cloud streets develop. With hardly any change in instability (no change in upper air temperature at 700 hPa compared to the east part of Denmark) the higher humidity (remember f.i. the higher dew points at 700hPa, fig 6) is important for the earlier start. And again, due to convergence at low levels in coastal regions (fig 4), convection is intensifying and smaller CU grow into larger CB clouds when reaching the north coast of Germany.
The Open Cell Convection, clearly noticeable in fig 4, over the North Sea and German Bight will not be discussed in this study.