Anchorage Windstorm of 1 December 1992

Abstract

On 1 December 1992 a strong downslope windstorm with an atypical damage pattern hit Anchorage. Downslope windstorms are common in Anchorage from September through April. Typically damaging winds from these storms are confined to the foothills of the Chugach Mountains and east Anchorage within 5 km of the edge of the foothills. In the 1 December storm, moderate wind damage occurred across the entire city in areas where wind damage is a rarity during downslope windstorms. Anchorage forecasters use an empirically derived automated technique to forecast downslope windstorms. The technique works very well. It is the purpose of this study to add to this technique so that atypical storms like the 1 December storm can be detected in advance. Historical records were searched and two storms with similar atypical damage patterns were found. In this study the 1 December windstorm is described, the two historical storms with similar atypical damage patterns are described, and a forecast tool is devised using a combination of characteristics common to the three storms that is hopefully unique. A by-product of this study is a synoptic-scale tool for forecasting the onset of maximum winds for the majority of Anchorage downslope windstorms.