Wind slabs continue to develop and are expected to be touchy on Thursday.Warm temperatures mean extra caution is required where smaller avalanches have the potential to step down to deeper weak layers that may still be reactive.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A pacific storm system is expected to reach the region on Thursday morning. 5-15cm of snowfall is expected on Thursday. Freezing levels are expected to hover around 1500m during the storm and alpine winds should be strong from the southwest. A mix of sun and cloud is expected for Friday with freezing levels around 1000m and light alpine winds. Light snowfall is being forecast for Saturday with models currently showing around 5cm.
Avalanche Summary
An early report from Thursday shows that explosives triggered a size 2.5 deep persistent slab avalanche on a south aspect at 2000m in the southeast of the region. This released down 70cm on the early December crust layer. No new avalanches were reported on Wednesday. On Tuesday, explosives triggered a size 3 persistent slab avalanches on an east aspect at 2000m. This released down 150cm on the early December crust layer.
Snowpack Summary
Recent strong to extreme winds from the southwest to west have redistributed the snow at treeline and above. Wind slabs have formed on lee slopes and windward slopes are being stripped away. Freezing levels are reported to be around 1900m on Wednesday afternoon. The mid and lower snowpack are getting stronger and settling well with the warm temperatures. A weak crust/facet layer from early-December is typically down over 1m. It has become difficult to trigger this layer but it is still reactive in snowpack tests suggesting that if you are able to trigger it, the layer is capable of wide propagations and large destructive avalanches. Recent explosive control triggered a few large avalanches on this layer in the southeast of the region. In the northwest of the region, there may still be reactive surface hoar layers in the upper snowpack.
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.