A cross section of the typical environment for the development of MCSs within the warm sector ahead of a frontal zone is characterised by the following typical features:

• The isentropes of equivalent potential temperature show a superadiabatic behaviour at mid-levels of the troposphere. A colder airmass overruns the lower warm airmass, resulting in unstable stratification.
• The vertical distribution of temperature advection is clearly characterised by WA at low and mid-levels of the troposphere and CA above.
• In the field of divergence, there is typically a convergence maximum at lower levels ahead of the frontal gradient of isentropes.

The diagrams above show a vertical cross section across the frontal cloud band and the MCSs which have developed ahead of it. In the cross section the MCSs are characterised by a peak of pixel values in the IR as well as in the WV image. The isentropes in this area show an unstable stratified troposphere (decreasing values of equivalent potential temperature with height) within the lower layers of the troposphere up to approximately 700 hPa.

The stability analysis of radiosonde stations show an unstable stratified troposphere within the lowest layers up to approximately 850 hPa (red). Between approximately 850 hPa and 600 hPa the troposphere is conditionally unstable. Above 600 hPa the radiosondes show stable and conditionally unstable layers. This column is typical for an atmosphere where Cb cloudiness or MCSs are likely to develop.

WA can be found in the lower levels and CA in the upper levels of the troposphere. WA can also be found at middle and upper levels, but the tendency for less WA at the upper levels still allows an unstable stratification to exist.

The field of divergence is not as pronounced as in the previous example. In the area of the MCS it is characterised by weak divergence in lower levels and weak convergence at upper levels.