Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period
Weather Forecast
Thursday: Increasing clouds throughout the day and moderate snowfall starting in the evening. Light winds increasing to strong southeasterlies with the onset of the storm. Freezing levels rising as high as 2000m, or higher in southern areas, but dropping in the evening. Friday: Heavy snow and strong southwesterly winds tapering off in the morning with 30-40cm total possible by the end of the day. Freezing levels are expected to drop to 700m. Saturday: Continued moderate precipitation and strong winds with freezing levels remaining in the 500-700m range.
Avalanche Summary
We received an initial report of an avalanche fatality in the southern Pemberton Icecap area on Tuesday. So far we know that a single snowmobiler was buried and perished in a Size 3 avalanche. The avalanche occurred on an east aspect at approximately 1700m, the slab was estimated to be 1.5-2.0m thick and 400m wide and suspected to have stepped-down to the mid-February persistent weakness. We will provide more details as they come available.
Snowpack Summary
Strong and variable winds in exposed treeline and alpine areas has resulted in reverse loading, sastrugi, surface crusts, and looming undermined cornices. Dribs and drabs of new snow over the past couple of days adds to the approximately 50cm of recent low density storm snow. Loose surface snow, storm slabs, and/or weak wind slabs are bonding poorly to a variety of old snow surfaces, including crusts, faceted snow, and wind slabs, from last week. Recent winds and precipitation patterns have created a highly variable somewhat upside-down upper snowpack. Storm and wind slabs have shown propensity to propagate in low angled terrain and step-down to deeper weaknesses.
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.