The cross section line extends perpendicularly through both cloud systems; but as the top left image shows, the two cloud systems represented by the orange lines are much closer together now: the peaks connected with the western cloud system are located between gridpoints 33/24 - 34/25, those connected with the eastern system between approximately 34/25 and 36/25 (compare Diagnosis for 06.00 UTC with help of vertical cross sections ).

Several features are similar to or even more pronounced than at 06.00 UTC: isentropes do not show any notable frontal zone; the only exception might be a very weak upper level Cold Front extending from the western to the eastern system between 300 and 400 hPa. There is some indication for a Cold Front from the cold advection connected with the western system which has now already reached the western parts of the eastern system. This has to be evaluated together with the WA below leading to even more pronounced lability in this area at 12.00 UTC. This is supported by several thunderstorm reports there and also (as described later in the chapter on thunderstorm development) by the appreciable development of thunderstorms from this point of time on. The top right image indicates the approach of the western system, also indicated by the PVA which has its maximum at 300 hPa, and is now much closer to the eastern system than before.

The bottom left image shows still a thick layer with non-frontal convergence for both cloud systems, which is also a good indication for an unstable situation.

All these parameters contribute to vertical motion which can be seen in the bottom right image as a very intensive and distinct feature showing upward motion for both systems, but with a maximum in the area of their mergence.