The relationship between synoptic weather patterns and snowpack stability in a high-latitude maritime snow climate

Weather is considered to be the architect of avalanche formation. Understanding its effects on snowpack properties is an important tool in avalanche forecasting. This study investigated regional synoptic weather patterns and their correlation to near-surface faceted crystal formation and snowpack stability in a high-latitude maritime snow climate. Regional synoptic variables were classified from charts published by the National Weather Service into three types 1) on-shore, 2) off-shore, and 3) split flow. Synoptic patterns were compared to plot scale meteorology and snowpack measurements collected at two study plots located at 700 m and 720m above sea level near Juneau, Alaska. Here we report on three episodes in January and February of 2004 in which vapor pressure gradients measured in the upper 25 cm of the snowpack were in excess of 45 mb m-1. During all three periods, faceted crystals 1-2 mm in diameter formed near the surface of the snowpack. In one case, wet grains comprising a low density crust at the surface of the snowpack metamorphosed into a weak layer of faceted crystals. Snowpack stability measurements following all three episodes revealed near-surface instabilities and avalanche cycles were observed after each of the events.