Isotachs and Positive Vorticity Advection at 300 hPa

In the region where the cyclogenesis starts, near the Bay of Biscay, there is a maximum of positive vorticity advection in the left exit region of a jet streak coming from the upper left corner. The advection of positive vorticity obviously favoured cyclogenesis in that region.

Six hours later the PVA in the Bay of Biscay is even stronger, but it is not directly in the region of the cloud spiral. In the Mediterranen there is no sign of the enhanced PVA.

As the cloud spiral in the Bay of Biscay develops further, the positive vorticity advection maximum intensifies and moves more to the south, across Spain. A closer look reveals that the jet is coming from the north towards Spain and curves across Spain. Also note that another maximum (jet streak) has formed over eastern Spain.

A PVA maximum is now in the Mediterranean, over the eastern coast of Spain.

Six hours later and the PVA maximum in the Mediterranean has further intensified. Also the development of clouds can be seen in that region. Although the distribution of the isotachs is such that an elongated narrow jet streak is not seen in the region, there is still a wind maximum across the Mediterranean and the vorticity advection maxima are related to that maximum.

The PVA in the Mediterranean gets even stronger while the clouds are forming a spiral shape.

Now the PVA maximum follows the cyclone as it moves towards Italy. A study of the isotachs makes clear that the PVA maximum are connected to the left exit region of the jet streak orientated from north Africa to south Italy.

Six hours later a pronounced PVA maximum is now over Adriatic.

Notice also the nice distribution of PVA maxima around the jet streak over northern Spain - there is a PVA maximum in left exit and right entrance region.

The pronounced PVA maximum, which is moving together with the cyclone, coincides with the more northern centre.

The system is dissipating and the PVA maximum is getting weaker.