From Glossary of Meteorology


Winds parallel to the main (longitudinal) axis of a mountain valley, resulting from the diversion of momentum from larger-scale winds above ridgetops into the valley.

Most commonly, direct transfer of momentum into the valley by mixing or by an impressed large-scale pressure gradient produces a flow along the valley axis that represents a component of the larger-scale flow, that is, in the same direction as the flow aloft. Occasionally, however, the perpendicular geostrophic wind relationship between the pressure gradient and the large-scale wind can lead to situations where the impressed pressure gradient produces a flow in the valley in the opposite direction to the along-valley component of the large-scale flow above the ridgetops.