Non-Orographic Convergence Lines
Lines of convective cells in advance of a Cold Front cloud band developing according to a diurnal cycle.
Lines of convective clouds which occur independently from orographic obstacles are mainly linked to frontal systems and appear in advance of frontal cloud bands or within the cold air behind a a frontal system. They are often more or less stationary or at least show a much slower propagation than the surrounding cloud systems. Like the orographically driven convective Convergence Lines the cloudiness is produced by upward motion due to low level convergence which is the result of different processes. Pre-frontal convective lines are influenced by an approaching frontal system as well as the diurnal variation of solar radiation. Consequently, the synoptic situation is changing during day.