24 November 2005: 12 UTC

Isotachs

The model fields of the isotachs in 300 hPA already showed a jet streak NW of the comma. However, the jet stream had a strong cyclonical curve and its axis might be found parallel to the rear egde of the front. The distribution of isotachs at 54°N supports this assumption.

Vorticity Advection

Compared to the situation 6 hours before, only one maximum of PVA is left. The two maxima of PVA connected with the comma and the cold front have merged according to the conceptual model. During the merging process the maximum of PVA overrides the frontal cloud band.

Temperature Advection

TA shows a similar situation to the image 6 hours before. The zero line of TA is connected with the cold front. A maximum of cold air advection can be seen in the area of the comma.

Divergence

We recognise a broad area of convergence (thick lines) in low- and mid-levels of the troposphere within the merging zone of the comma and the cold front.

Vertical Motion

Strong upward motion can be found in the area of the comma cloud feature on the rear side of the cold front (55°N/1°E). Ascending air is also connected with the rear of thze cold front (54°N/4°E). Because of the separation of both areas it is clear that comma and cold front did not yet merge.

Potential Vorticity

The potential vorticity still shows a PV anomalies in the area of the comma. The entire region of high PV moved to the Southeast