A Coastally Trapped Wind Reversal Along the Gulf of Alaska

Coastally Trapped Wind Reversals (CTWR) are associated with a change in wind direction, decrease in temperature and sudden increase in stratus cover which often impact aircraft and boating activities. CTWR have been thoroughly studied along the west coast of the United States but may occur along the Gulf of Alaska as well. On June 9, 2008 GOES-11 satellite imagery indicated the formation of stratus east of the Copper River Delta that propagated along the southern islands of Prince William Sound. After reaching the end of Montague Island the stratus continued to propagate offshore but eventually split and propagated both east and westward.

Surface observations indicate that the propagating stratus feature had characteristics similar to those associated with CTWR events. A general increase in pressure, decrease in temperature and transition to coast parallel wind flow were observed throughout its propagation. The synoptic set-up for the CTWR was similar to that observed in previous CTWR studies including the inland extension of a ridge and the persistence in offshore flow which results in the extension of the Yukon and Alaska thermal trough.

The University of Wisconsin-Nonhydrostatic Modeling System (UW-NMS) was used to further explore the structure and dynamic characteristics of the wind reversal. Three nested grids of 30km, 6km and 2km horizontal resolution were used with a vertical resolution of 100m for the first 1500m. Model output indicated that throughout much of its propagation the wind reversal resembled a density current. Several other interesting features such as gravity waves and a topographically trapped low were also observed in the model run.