Avalanche activity on the tricky mid-Dec weak layer has decreased recently but this layer should still be treated as a major hazard for the foreseeable future. Large and destructive human-triggered avalanches remain possible.
Weather Forecast
A ridge of high pressure will keep things dry for Wednesday and Thursday. A temperature inversion should keep the valleys cooler and under fog but above the fog should be mostly sunny. Alpine winds should remain light on Wednesday and Thursday morning but will progressively increase on Thursday afternoon. The next frontal system should reach the interior on Thursday night but is only expected to yield 5-10cm. By Friday afternoon the system should be finished and sun is expected. Alpine winds should be moderate-to-strong from the SW during the weak frontal system.
Avalanche Summary
No new avalanches have been reported since Saturday. On Saturday, ski cutting produced a size 1 avalanche with a depth of 25cm. This was reported to have released on the mid-Dec surface hoar layer. Natural avalanche activity is not expected on Wednesday but remains possible (isolated), especially on solar aspects when the sun is out. A small avalanche could trigger a larger persistent slab. Skier triggering a persistent slab avalanche remains the main concern for the foreseeable future.
Snowpack Summary
A layer of surface hoar up to 10mm sits on the snow surface. A sun crust exists on steep sun exposed slopes. Recent warm temperatures have aided in the settlement of the week old storm snow. The persistent slab is typically 40-80cm thick and sits on the mid-December surface hoar/crust layers which remains sensitive to human triggering. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive at treeline or just below treeline. The mid-Nov weak layer is near the bottom of the snowpack but has become inactive.
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.