Isotachs and Positive Vorticity Advection at 300 hPa

The solid yellow lines north of the Great Britain indicate the jet stream. The zero line of shear vorticity (black solid line) shows the location of the jet axis. In the left exit region of the jet streak a strong PVA maximum (red solid lines) is present and it is in exact agreement with the intensified cloud area south-east of Scandinavia.

The intensification of the cloud band due to the PVA maximum in the left exit region is expanding. Notice also another PVA maximum west of the Great Britain in the right entrance region of the jet stream, showing nicely the distribution of the vorticity advection around the jet maximum. The theoretical background for this can be found in Physical Background chapter.

Jet streak has maximum wind speed up to 70 m/s. Looking at the zeroline of shear vorticity it is seen that the jet crosses the cloud band almost perpendicularly. Enhancement by the PVA maximum in the left exit region of the jet streak is evident. The three maxima can be observed near the jet stream, two of it in the left exit region. The PVA maximum is an indication for further intensification and further development.

As seen also 6 hours before, the jet crosses the frontal cloud band almost perpendicularly. Two maxima of PVA are clearly visible - one over Poland, and the other over Austria.

The maxima over Austra is divided into two parts. The stronger one is connected to the main part of the intensified cloud band whereas the other maximum is superposed over the second intensification.

The system is moving further to the south-east still with two maxima.

At this point there is again just one PVA maximum over south Croatia and south Adriatic. The clouds are more convective type, because of the cold advection. The convective clouds are connected to upper level trough as can be seen at AT500 hPa field.

The very dominant Jet streak can be seen from south Scandinavia, over Poland and Hungary, down to Croatia. The PVA maximum remained in its position in the relation to the Jet streak and the cloudiness under it is connected with intensive precipitation.

The cloud band is moving to the south-east and dissipating, and the PVA maximum is weakening.