Regions
Northwest Inland.
The March 9th persistent weakness is very sensitive to human triggering and has produced frighteningly large avalanches. Stay conservative in your approach to the mountains this weekend
Confidence
Fair - Due to limited field observations
Weather Forecast
Synopsis: Fine weather for the Sunday. A very weak system will bring cloud and flurries for Monday and Tuesday.Sunday: Clear and sunny. Daytime alpine temperatuers around -5, but feeling warmer in the sun. Light winds.Monday and Tuesday: Cloudy with occasional flurries. Afternoon freezing level rising to around 1100 m. Southeast winds to 30 km/h.
Avalanche Summary
No new avalanches were reported on Friday. On Thursday, human-triggered avalanches were reported running on a the March 9th surface hoar layer on north and northwest aspects. Natural avalanches up to size 2 were also observed on lee slopes below steep ridge lines. On Wednesday, there was a natural cycle to size 3. Skiers were remote triggering large destructive avalanches (size 2.5) from as far as 800m away. It has been an active recent period, with numerous avalanches reported to have failed on the March 9th layer over the past week.
Snowpack Summary
35 - 65 cm of recent snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and a buried surface hoar layer (March 9th). The March 9th surface hoar layer has been very touchy in many areas and many large avalanches have released on it. While natural avalanche activity on this layer has diminished, snowpack tests showing very easy shears reinforce this layer should not yet be trusted. The distribution of the surface hoar is slightly variable and it may not exist, or be reactive, in every drainage. Where it does exist, it appears to be present at all elevations, but is likely to pose the biggest threat in the alpine. Recent reports indicate it has been more reactive on south through west aspects, but I wouldn't necessarily trust steep north or east facing slopes at this time either. I suspect cornices have become well-developed and could easily become unstable during periods of warm weather or on slopes receiving direct sun. The mid snowpack is generally well settled and strong.
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.