Title

Synoptic-scale Weather Patterns and Large Slab Avalanches at Mt. Shasta California

Document Type

Article

Publication Date

2012

Publication Title

Northwest Science

DOI

10.3955/046.086.0408

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.