Regions
Northwest Inland.
Confidence
Fair - Due to limited field observations
Weather Forecast
The inland sections of the North Coast may only see high cloud and very little precipitation as the existing low diminishes. Tuesday: Light precipitation near 5 mm. Ridgetop winds will blow moderate from the South West. Alpine temperatures steady near -5.0 and freezing levels hovering around 1000 m in the afternoon.Wednesday/Thursday: Mainly dry conditions with lingering valley cloud. Ridgetop winds blowing light from the SouthWest. Alpine temperatures near -6.0 and freezing levels at 900 m in the afternoon.
Avalanche Summary
On Sunday, natural avalanche activity seemed to taper off. However, there was one report of natural icefall size 2.0. Natural cornice fall is expected through the forecast period with warmer afternoon temperatures and solar radiation. Over the past week skiers were remote triggering large destructive avalanches (size 2.5) from as far as 800m away. It has been an active period, with numerous avalanches reported to have failed on the March 9th layer. This layer is still a concern, but may trend to a low probability-high consequence scenario.
Snowpack Summary
Strong winds have redistributed storm snow on lee aspects creating stiff wind slabs. 35 - 65 cm of recent snow sits 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. Recent snowpack tests are showing very easy shears which means this layer should not yet be trusted. The distribution of the surface hoar is 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 trust steep north or east facing slopes at this time either.Cornices have become well-developed and could easily become unstable during periods of warm weather or on slopes receiving direct sun. Most snow surfaces exist on solar aspects up to 2300 m, forming a melt-freeze crust overnight.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.