Surface and upper air meteorological data gathered by the MesoWest cooperative for the years 1997-2001 are used to study the effects of dynamic channelling of airflow over the Upper Snake River Plain in Idaho, USA. The Upper Snake River Plain is a curved valley with a broad, u-shaped cross section. The valley floor height decreases from about 1500 m asl in the east to about 900 m asl in the west. The elevations of mountain ranges bounding the valley to the north and south reach up to about 3000 m and 2100 m asl, respectively.

Data measured during days with strong upper level winds and (at least partly) cloudy conditions are selected to exclude effects of thermally induced circulations in the area. The direction and speed of surface winds over the Upper Snake River Plain are studied as a function of dynamic forcing and atmospheric stability derived from upper air soundings in Boise, which is located towards the western end of the Upper Snake River Plain. The occurrence of pressure driven and forced channelling at various surface stations along the valley axis is investigated by correlating surface and upper air wind observations. Possible implications of the results for the dispersion of air pollutants, propagation of bush fires and aviation are discussed.