Continued strong winds will keep the avalanche danger elevated. Be alert to conditions that change with elevation.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Wednesday: Overcast skies / Extreme southwest winds / Freezing level at valley bottomThursday: Mix of sun and cloud / Extreme southwest winds / Freezing level at 1200Friday: Mix of sun and cloud / Extreme southwest winds / Freezing level at valley bottom
Avalanche Summary
Numerous storm slab avalanches (mostly in the size 2 range), were observed failing naturally on Tuesday. The avalanches formed in response to heavy storm loading and failed mostly on north to northeast facing terrain at treeline and in the alpine. Looking forward, continued extreme southwest winds are expected to promote ongoing wind slab activity. There is a bit of uncertainty regarding how the new snow will bond to old surfaces which formed during last week's cold snap. Due to these potentially persistent weak layers, recently formed storm slabs may remain sensitive to human triggering for some time.
Snowpack Summary
Since Sunday up to 60cm of low-density snow has fallen with the highest amounts accumulating in the Lizard Range. Strong winds and slight warming have added cohesion to the new snow and reactive storm slabs exist in wind-exposed terrain. The new snow buries a variable surface that developed over the last week of cold, dry, and windy conditions. This interface consists of scoured surfaces and wind slabs in wind exposed terrain, widespread faceting of the upper snowpack, and surface hoar up to 20 mm in sheltered areas. In sheltered areas, you may find another layer of surface hoar in the mid to upper snowpack which was buried around December 10. The mid pack is generally well settled. The thick crust from mid-November is near the bottom of the snowpack and reports suggest that the crust is currently well bonded to the surrounding snow.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.