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University of Washington: "Improved characterization and prediction of Taku windstorms"

Final Report

During the wintertime in southeast Alaska, the Juneau WSFO forecasters are confronted with forecasting some of the most dramatic, persistent, and severe downslope winds in North America. The northeast Taku winds near Juneau can reach surface speeds in excess of 50 m/s when cold Canadian continental air spills down the Taku River Valley and across southeast Alaska. These northeast windstorms can cause extensive property damage, significant disruption of local activities, and pose a life-threatening hazard. In fact, northeast windstorm events have historically been responsible for more local weather-related deaths and property damage than all other Juneau area weather phenomena combined. The Taku winds appear to have much in common with downslope winds such as the Yugoslavian Bora and the Colorado Chinook, in that very strong winds are observed to sweep down the steep lee slope of Salisbury Ridge. Unlike the Bora and the Chinook, however, significant winds are also found in a cross-mountain gap at the mouth of the Taku River. One of the primary goals of this project is to improve our understanding of, and our ability to forecast, these two related flow regimes.

One of the primary efforts of the project was devoted to the collection of data to better characterize the two regimes. In order to accomplish this, two new observation sites (with wind, temperature, and pressure sensors) were established. Several other sites were equipped with more modest instrumentation (wind recorders and/or recording barometers). Unfortunately the winter of 1992-1993 was almost completely free of wind events. The instruments were also operated in 1993-1994 in the hopes of obtaining a decent data set.