Touchy conditions still exist in many parts of the region. A warm, wet and windy storm will cause conditions to deteriorate.
Confidence
Moderate - Track of incoming weather systems is uncertain on Thursday
Weather Forecast
15-20mm of precipitation is forecast for Wednesday night with another 15-20cm of snow expected on Thursday. Ridgetop winds will remain extreme from the southwest while freezing levels will drop throughout the day from 2000m to about 1500m. On Friday and Saturday the region will see generally light flurries, significantly decreased winds and freezing levels around 1000m.
Avalanche Summary
In recent days, backcountry avalanche observations have been extremely limited, mostly due to stormy weather. That said, I suspect persistent weaknesses have remained sensitive to human triggering, especially in the north of the region where very touchy conditions were reported to persist. Looking forward, continued warm, wet and windy weather is expected to spark ongoing storm slab activity in high elevation lee terrain, but warm temperatures and loading will also increase the likelihood of waking up any lingering persistent weaknesses that were not triggered by last week's storm.
Snowpack Summary
On Wednesday and Thursday, moderate snowfall and strong winds will continue to form deep and dense storm slabs in high elevation terrain and cause substantial cornice growth. At lower elevations rain is forecast to further saturate the upper snowpack. In some areas, last week's storm and the resulting avalanche cycle helped flush-out the mid and early-January surface hoar/facet layers now down 60-120 cm deep. However, these layers are still intact and reactive in many places and it may still be possible to trigger large slabs. The mid and lower snowpack is generally strong, with the exception of shallower snowpack areas that may be more faceted.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.