One of the most distinct features is a pronounced lowering of the PV-2 unit to heights of 400-500 hPa. This lowering of the dynamical tropopause is regarded as the upper level PV anomaly (see also Additional Parameters Indicative Of The Diagnosis Of Cloudiness: Potential Vorticity ).
If this anomaly propogates over time, then ahead of the anomaly, positive vorticity advection occurs and to the rear, there is negative vorticity advection.

A large area of cold advection can very often be found near the PV anomaly. There is a forward tilt of the advection pattern, resulting in increasing cold advection with height (and therefore destabilisation). To the rear of the PV anomaly, an area of warm advection can often be found which may indicate an approaching new frontal system.

Just below the PV anomaly, at mid-tropospheric levels, the strongest upward and downward motion can be found.
Although cold advection and the vorticity advection tend to counteract each other, a maximum of upward motion can be detected, indicating that the contribution of vorticity advection must be larger than that of temperature advection. (see also Numerical Parameters Indicative Of The Production Of Cloudiness: Omega Equation ).

A sharp gradient of isentropes near the surface indicates the surface cold front (CF). To the rear of this CF, high values of ThetaW occur. The ThetaW inversion at levels between 700 and 800 hPa characterises an airmass which is potentially unstable. This causes, together with dynamical forcing, upward motion and subsequent convection.
In the higher troposphere, behind the PV anomaly, there is a marked inflow of dry air with stratospheric origin, caused by strong downward motion. In WV imagery this can be seen as a narrow dark zone. To the rear of the CF, the relative humidity is high, especially at lower levels. This provides a supply of moisture for the development of convection.

PV and PVA

At 42N/02W a distinct lowering of the 2 PVU isoline can be seen towards levels of approximately 400 hPa. To the east of the PV anomaly, where there is enhanced convection, a maximum of PVA can be seen between 300 and 400 hPa. To the rear, where the dark stripe is found, there is a pronounced minimum of NVA.

PV and TA

At 42N/02W, around the PV anomaly, there is a distinct area cold advection that usually occurs behind the frontal zone. The forward tilt of the cold advection pattern can also be seen.

PV and Omega

The strongest vertical motion can be found at levels where the vertical gradient of vorticity advection shows a maximum. Another maximum of vertical motion at 39N/05E is associated with the frontal zone.

PV, Theta_W and Relative Humidity

The surface cold front is located at approximately 41N/03W. The isentropes show a distinct gradient at lower levels. Just east of this gradient, the values of ThetaW and relative humidity in the lower levels are high, resulting in a potentially unstable stratification.