27 February 2004: 18 UTC

This is the transition phase. The cross-section is laid through both the old cyclone, coming from the Bay of Biscay, and the new one, developing in the Mediterranean. The isentropes clearly indicate this twofold structure: there are two very similar regions in the cross section.

Potential Vorticity

Positive PV anomaly is still connected mainly to the old cyclone, the one on the left-hand side of the cross-section, but it is getting weaker and the height of PV=1 unit is now around 500 hPa. However, there are still rather high values near the ground.

Vorticity Advection

Strong PVA maximum is found in the lower layers, connected to the old cyclone. The value of vorticity advection is getting smaller with height, contributing to the sinking motion and dissipating of the old cyclone. In the region where the new development occures there is a PVA maximum in the upper levels, but that one is shifted more to the right (in the right-hand corner of the cross-section) and is not directly coinciding with the cloud band.

Temperature advection

There is strong warm advection in the upper levels above both systems. Underneath, two weak cold advection maxima can be seen, but at this stage this twofold structure is still not very pronounced.