Curvature vorticity is due to the increasing cyclonic turning as an air parcel enters the trough base.
Shear vorticity is caused by the difference in wind speed between air moving through the trough base (typically a jet or jet finger) and slower moving air on either poleward and equatorward side of the faster flow.
[citation needed] This produces convergence because of the way the air gains cyclonic vorticity while entering the base of the trough.
This forced lift, in the presence of conditions favorable for atmospheric convection, can cause clouds or precipitation.
In combination with a jet streak, CVA can lead to the amplification of a trough which is significant for forecasting many conditions of the atmosphere.