As can be seen in the left image a distinct PVA maximum at 300 hPa coincides very well with the area of the western cloud system while there is only weak PVA for the eastern system. This PVA maximum is still connected with a maximum of shear vorticity (right image) representing a jet streak. The axis of this streak can also be diagnosed with help of the cloud fibres over the North Sea which are parallel and in good agreement with the zeroline of shear vorticity.