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Avalanche Forecast

Archived

Apr 12th, 2015–Apr 13th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

This forecast has been prepared with very few field observations. If you have observations to share here, we`d love to hear from you.

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

Cool unsettled spring time weather will bring small amounts of precipitation between Pacific weather systems for the next few daysMONDAY:  5 to 10 cm of snow. Precipitation will be heavier towards the coast, but the inland portion of the coast will also see snow at higher elevations. Winds from the south, moderate to strong with the freezing level rising over 1000m.TUESDAY: A brief break in the weather, cloudy with sunny periods, some flurries with freezing levels around 500m. Winds moderate to strong from the south.WEDNESDAY:  A Pacific frontal system arrives on the coast bringing  up to 20cm of snow to the higher elevations. Freezing level around 800m with moderate to strong winds from the south

Avalanche Summary

No reports of natural or skier / rider triggered avalanche in the past few days, probably because of the storm cycle and lack of visibility for field observations.

Snowpack Summary

New snow is being redistributed by strong south west winds into wind slabs on lee slopes. Reports of activity on the March 25th surface hoar / crust layer have diminished, but is still worth remembering. This interface was more reactive recently in the northern part of the region, but had been reported throughout the northwest coastal area and may reappear as a problem given the right conditions.  For the most part, the chief concern  right now is wind slabs over a variety of recent surfaces, crusts, facets and surface hoar that formed in in sheltered places during the last spell of clear cold weather.  Large ripe cornices are also of concern with additional loading, especially when the sun and warm temperatures come back.

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.

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.