A layer of potentially warm air (see potential temperature) that originates over the Iberian Peninsula and flows north towards France. It forms a capping inversion that restricts small-scale convection in the lowest layers, which become extremely humid. The arrival of an eastward-moving upper trough leads to the breakdown of the inversion and the development of multicell or supercell thunderstorms over France, which often cross the English Channel into southern England. Similar to the Mexican plume in the southern United States.
Subjects: meteorology and climatology.