REGIONAL DRAINAGE FLOWS IN THE PACIFIC-NORTHWEST

An analysis of regional drainage flows in the Pacific Northwest is presented using results from a network of surface observations and a series of simulations carried out with a nested mesoscale model. The flows, which occur regularly in southeastern Washington during the late spring and summer months, are marked by an increase in wind speed and a shift to northwesterly wind directions early in the evening. The phenomenon occurs when a deep mixed layer forms east of the Cascade Range, drawing cooler air from the west over the mountain crest. Anabatic and katabatic forcing, terrain channeling, and turning by the Coriolis force combine to produce the characteristic flow patterns.