Strong Westerly Wind Events in the Strait of Juan de Fuca

Abstract

trong westerly wind events occur regularly within and downstream of the Strait of Juan de Fuca of Washington State. During such strong gap wind periods, flow can accelerate to 30?50 kt (1 kt = 0.51 m s?1), with gusts sometimes reaching 80 kt or more. Strong winds in the strait and downstream of its eastern exit have caused substantial damage and loss of life. Strait of Juan de Fuca westerly wind events are often associated with sharp short-wave troughs coming out of the northwest, strong lower-tropospheric northwesterly geostrophic flow roughly paralleling the axis of the strait, and a large along-strait pressure gradient near the surface. Strong westerly flow in the strait also accompanies the passage of intense low pressure centers across northwest Washington State and southern British Columbia. The climatology of westerly wind events in the strait is presented, as well as their composite synoptic evolution. Using both mesoscale observations and high-resolution numerical simulations, it is shown that modern modeling systems can realistically simulate the mesoscale evolution of strait wind events. It is shown that strait gap wind events are associated with downward mixing of strong gap-parallel geostrophic winds in the lower troposphere and acceleration down a low-level pressure gradient produced by the passage of a synoptic trough and terrain-induced pressure perturbations.