An Aleutian Island Wind Event

On the evening of December 4 2009, wind speeds gusted to a recorded 115 mph in Dutch Harbor on Unalaska Island, Alaska. These intense gusts were imbedded within average wind speeds of only 20 mph to 30 mph and were preceded by wind gusts that averaged only 80 mph. Although the event occurred within the data sparse region of the Aleutian Islands, the intense irregular wind gusts and proximity to mountain peaks of 1500 ft suggests that mountain waves may have contributed to the intense winds. A two-way nested high resolution UW-NMS (University of Wisconsin-Nonhydrostatic Modeling System) run indicates the presence of non-breaking mountain waves forming across the complex terrain of Unalaska Island. Several factors appear to contribute to the formation of this mountain wave event. On the evening of December 4, a 956 mb low reached its peak intensity just north of Unalaska Island. At this time, an associated low level jet with wind speeds greater than 110 mph was perpendicular to the mountain ranges on Unalaska Island. In addition, a slightly stable layer of air existed near the surface.