New wind slabs have formed in the alpine and at tree line. Cornices continue to grow with new snow and wind.
Confidence
Moderate - Due to the number and quality of field observations
Weather Forecast
A short intense pulse of moisture brought 5 to 15cm of snow Friday night. Gradual clearing should give mostly clear skies on during the day on Sunday. On Monday afternoon night the region may see light flurries, with clearing on Tuesday and through the rest of the week.. Ridgetop winds are forecast to be light to moderate from the southwest with freezing levels rising during the day and falling to valley bottoms at night.
Avalanche Summary
Avalanche observations for the region have been extremely limited, mostly due to stormy weather. New snow and wind on Friday night will likely promote a round of wind slab activity in high elevation lee terrain.
Snowpack Summary
New snow and wind on Friday night will have formed new wind slabs in lee terrain at treeline and in the alpine. Up to 15cm of precipitation fell Friday night. In addition, the stormy weather has encouraged new cornice growth. These cornices may rbe huge and unsupported. About 30-50cm below the surface you may find a melt freeze crust which formed during the 2nd week of February. At the same interface, you may also find surface hoar which most likely exists on high, north facing terrain. Recent rain and warm temperatures at lower elevations have likely flushed out this weakness in most areas; however, continued reactivity may exist in high elevation terrain above the recent rain line. West of the divide, a layer of buried surface hoar can be found between 70 and 90cm below the surface. Recent reports suggest this layer has become less of a concern.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.