25 November 2005: 00 UTC

Isotachs

Because the jet stream's axis is almost parallel to the cross section this image reveals only low wind speeds in the jet niveau and over France. .

There is a maximum of the isotachs near the surface. The axis perpendicular to the cross section. This is the area of strong northern winds on the western side of the surface low, which was registered as heavy storms on the west coast of the Netherlands.

Vorticity Advection

The maxima of PVA were less pronounced at this time and only connected with the cold front. The comma which completely merged with the cold front was imposed by NVA.

Temperature Advection

Warm air and cold air advection do not show pronounced maxima at this time. The surface low remained almost stationary during the next about 18 hours.

Divergence

Fields of convergence (thick lines) are found at the tail of the occlusion spiral and at the cold front. Divergence was connected to the dry area within the cloud spiral.

Vertical Motion

A maximum of upward motion was associated with the field of convergence in the tail of the occlusion spiral indicating ongoing cloud development and precipitation.

Potential Vorticity

Two relative PV Anomalies coincide with the dark areas that can be seen even better in WV images. Stratospheric air was involved in the cyclonic air flow and obviously reached to the centre of the cloud spiral. The area of high PV moved fast to the Southeast.

This cross section reveals an instructive example for PV-patterns during a rapid cyclogenesis. At about 52.5°N and 6°E we see relative high PV-values penetrating to 600 hPa. About 100 kilometres farer to the East a further PV-maximum can be seen in lower levels (around 10°E and at about 850 hPa) that is combined with a baroclinic zone. That is the process of a rapid cyclogenesis according to the Hoskins theory.