The diurnal cycle of local winds between a mountain or a mountain range and the adjacent or surrounding plains during periods of weak synoptic flow. Winds at lower elevations blow from the plains toward the mountains during daytime and from the mountains toward the plains at night. An upper return branch of the circulation at higher levels is sometimes present, blowing in the direction opposite the surface winds and completing the circulation. The mountain-plains wind system is most apparent on individual days when skies are clear and the general prevailing winds are weak, but it is also seen in climatological averages. The term is usually used to represent the larger massif-scale circulations, of which the embedded along-valley wind systems and along-slope wind systems are key components. On the smaller mountain and mountain-range scale, the components of the diurnal cycle are a nocturnal mountain (katabatic) wind and a daytime wind from the plains toward the mountains (anabatic wind).