Warm, Wet, and Windy storm will create new wind slabs and add load above the persistent weak layer. Conservative terrain use recommended at this time.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Light snow with southwest winds increasing to strong overnight. Freezing level around 1500 metres overnight and rising to about 1700 metres on Thursday. 5-10 cm of new snow with strong southwest winds on Thursday. Winds decreasing to moderate westerly combined with light snow and dropping freezing levels on Friday. Overcast with flurries and light winds on Saturday.
Avalanche Summary
Some skier controlled wind slab avalanches up to size 1.5 were reported on Tuesday from various alpine aspects. One size 2.0 avalanche released sympathetically to a skier controlled avalanche. No new natural avalanche activity was reported. I suspect that wind slabs have continued to develop in the alpine and at treeline on Wednesday.
Snowpack Summary
Most areas are reporting new wind slabs that are 10-25 cm deep, that have developed from moderate to strong southwest winds. Old storm snow amounts are variable across the region from 30-60 cm, and continue to produce settlements and moderate sudden planar test results. The early January persistent weak layer of buried surface hoar continues to be a concern for human triggered large avalanches. Reports indicate this persistent weak layer is now typically down 40-70 cm in most areas and appears to be quite touchy in some parts of the region. A more deeply buried layer of surface hoar from December is now considered dormant. In general, the lower snowpack is well settled and strong.
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.
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.