Regions
Northwest Coastal.
The danger ratings reflect the hazard in the Northern part of the region, where a notable persistent weakness has been very touchy recently. This problem could be more widespread than we know.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Thursday: Increasing cloud with snow possible late. The freezing level is around 1400-1500 m. Winds increase to strong or extreme from the S-SW. Friday: Moderate to locally heavy snow 20-30 cm. The freezing level is near 1000-1200 m and winds are strong from the S-SW. Saturday: Cloudy with periods of snow. The freezing level is around 800 m and winds are moderate from the SW.
Avalanche Summary
Note: Almost all of the recent reported activity is from the Northern part of the region near Ningunsaw Pass. This could be because this is the hot spot at the moment, but it could also be because there are few observers in the field further south. For the past few days, there have been reports of natural, skier-triggered, and remotely triggered slabs up to size 3 releasing on the March 25th surface hoar layer. Some of these have been triggered from below or in low-angle terrain. In addition, cornices have been failing and loose wet activity has been noted in the afternoon, both of which have triggered deeper persistent slabs.
Snowpack Summary
The snow surface varies from dry faceted powder and/or surface hoar on shady slopes, to moist snow or a sun crust on sunny slopes. In some places down-flowing winds have created thin wind slabs in lee features lower down the mountainside. Approximately 40-70 cm of snow sits above the March 25th surface hoar layer. This interface seems much touchier in the northern part of the region, but has been reported throughout the northwest coastal area. The early March facet/crust persistent weakness is now down over a metre and produces hard, sudden planar results in snowpack tests.
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.