When cold air intrudes into the upper levels of the troposphere, it increases the density of the air in these regions, leading to a decrease in the height of pressure surfaces. This results in the formation of an upper-level trough, which is characterized by lower heights and lower pressures compared to the surrounding areas.

Upper level troughs can result in the formation of a cloudbands, which will often result in widespread rainfall near and to the east of the trough (development of showers and thunderstorms). Upper level troughs can also aid in the development of surface level features, such as frontal systems, thereby enhancing their effect. The presence of an upper level trough in a favourable position may result in the development of a cut-off low, which in turn will enhance rainfall over the affected region.