Item: Westerly Wind Bursts Affect Avalanche Cycles
Title: Westerly Wind Bursts Affect Avalanche Cycles
Proceedings: Proceedings Whistler 2008 International Snow Science Workshop September 21-27, 2008
- Melinda M. Brugman [ Pacific Storm Prediction Centre, Vancouver, BC ]
- Matthew MacDonald [ Pacific Storm Prediction Centre, Vancouver, BC ]
Abstract: Recent climatology and basic physics provide new incite into how major westerly wind bursts contribute to avalanche cycles. A more complete understanding of these westerly wind events can help improve our weather forecasting for winter seasons in western Canada. This study examines the role the major storm events in the years 2006-2008 played in mountain snow accumulation, snow redistribution, freezing level fluctuations and snow stability across western North America. Severe weather systems that deepen rapidly are the focus of this paper. These storms produced unusually heavy snowfalls and have recently been linked to strong westerly wind bursts (WWB's). Our analyses show that a quasi 40-60 day oscillation circumnavigates the globe and is associated with westerly wind bursts at 500 mb (for mid latitudes between 35oN and 55oN). These mid latitude WWB oscillations at 500 mb occur in a fashion similar to the well known Madden-Julian Oscillations (MJO) oscillations which occur at 850 and 200 mb. Preliminary results suggest the a Wheeler-type (phase, longitude strength) diagram for the entire globe (or the pacific segment) may allow better tracking of these WWB impulses. The 500 mb wind anomalies may be derived from both model forecasts and direct observation (such as satellite cloud motion data). Using this information we can better understand factors controlling recent major avalanche cycles in western Canada, and better track WWB cycles that appear to be related.
Language of Article: English
Presenters: Dr. Melinda Brugman, Dr. Matthew MacDonald.
Keywords: westerly wind bursts, mid-latitude, avalanche cycles