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 super adiabatic behaviour at mid-levels of the troposphere. A colder air mass overruns the lower warm air mass, resulting in unstable stratification.
• The vertical distribution of temperature advection is clearly characterised by warm advection at low and mid-levels of the troposphere and cold advection above.
• In the field of divergence, there is typically a convergence maximum at lower levels ahead of the frontal gradient of isentropes.

Isentropes

Temperature Advection

Divergence

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 an unstable stratification seen ahead of the frontal system around 44N/4E. These unstable stratified isentropes (decreasing values of equivalent potential temperature with height) reach the lower layers of the troposphere, up to approximately 700 hPa.
WA is associated to the MCSs and will contribute slightly to the upward motions. Not surprising, WA is found ahead and aloft of the Cold Front in the area of the Warm sector.

In the divergence field a pronounced maxima of convergence can be seen near the surface in the area of the warm sector. Aloft there is divergence causing outflow of air.