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1 September 2012 Synoptic Scale Weather Patterns and Size-5 Avalanches on Mt. Shasta, California
Cassandra Hansen, S. Jeffrey Underwood
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Abstract

Upper atmospheric synoptic scale patterns associated with size-5 avalanches, the largest and most destructive types of avalanches, occur on Mt. Shasta, California in the Southern Cascade mountain range. We identified and analyzed fifteen size-5 avalanches over nine individual storm events in the last 50 years using composite and anomaly plots of surface and upper-air data and relationships between: 250hPa wind field, 500 hPa geopotential height field, 700 hPa precipitable water, atmospheric thickness, and surface temperature. Results indicated a strong correlation between synoptic scale warm air advection, moisture advection, strong southwest winds, and low geopotential heights and the formation of large, size-5 slab avalanches. The identification and orientation of a jet streak adds to the growing body of synoptic ingredients used for avalanche forecasting on Mt. Shasta.

© 2012 by the Northwest Scientific Association. All rights reserved.
Cassandra Hansen and S. Jeffrey Underwood "Synoptic Scale Weather Patterns and Size-5 Avalanches on Mt. Shasta, California," Northwest Science 86(4), 329-341, (1 September 2012). https://doi.org/10.3955/046.086.0408
Received: 12 December 2011; Accepted: 25 June 2012; Published: 1 September 2012
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KEYWORDS
Northern California
Size-5 Avalanches
Synoptic weather
West Coast
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