19 November 2004: 12 UTC

Potential Vorticity
The situation at 12 UTC shows the dynamical tropopause (PV=2) lowered down to 450 hPa. This PV anomaly corresponds excellently to the area of dry air between the cloud head and the cold front. The dynamic development of this PV anomaly can be studied by comparing this image with the vertical cross section six hours later.

Isotachs
The field of isotachs shows a distinct situation. The SW-jet stream is connected to the dry slot. The isotachs show a pronounced jet stream along the rear edge of the cold front and a sharp gradient towards the cloud head. A second jet stream exists at the poleward side of the cloud head.

Temperature Advection
Strong cold advection is related to the dry area. The zeroline of TA indicates the position of the cold front. A typical maximum of WA in the area of the cloud head cannot be seen at this time step.

Vorticity Advection
The field of vorticity advection shows a PVA maximum in the area of the dry tongue. PVA is also situated in upper layers within the area of the cloud head. NVA is found on the other side of the dry tongue in the gradient zone of the cold front.

Relative Humidity
The field of relative humidity clearly reveals the typical dry tongue. Low values can be found to relatively low levels in the atmosphere.