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Avalanche Forecast

Archived

Apr 15th, 2014–Apr 16th, 2014

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

Regions

Northwest Coastal.

This bulletin has been produced using very limited field data. If you've been out in the mountains we'd love to hear about what you've seen. Observations can be sent to [email protected]

Confidence

Fair - Due to the number of field observations

Weather Forecast

Tonight and Wednesday: A frontal system is forecasted to approach the coast spreading light to moderate precipitation (~15 mm in water equivalent) into Wednesday. Freezing levels around 1200 m with moderate South East winds. Thursday: Heavy precipitation is expected (~30 mm) with freezing levels around 1100 m and moderate to strong winds from the South West. Friday: A break in precipitation before the next system approaches the coast late in the day. Freezing levels around 1100 m and light South winds.

Avalanche Summary

A slab avalanche size 2.5 was remotely triggered yesterday on a North facing alpine slope in the North Eastern part of the region. This slab would have run on the deep persistent weak layer buried in mid-February. 

Snowpack Summary

Forecasted light to moderate accumulations mostly over the Southern part of the region should fall over a surface crust on solar aspects up to around 1400 m or onto last week's storm snow which brought 90+ cm or more to the coastal region.  This storm layer is expected to bond poorly to the underlying surfaces and to form touchy windslabs in the alpine lee of the forecasted moderate South East winds.Recent warmer temperatures have helped to settle the underlying snowpack. Although, it has been reported to be reactive to skier traffic on steeper/shallower slopes since it is where it is sitting on a surface hoar, crusts and/or facets buried at the beginning of April. Large cornices have formed and loom over slopes below. The early February crust/facet layer is down 150 - 240 cm. An avalanche could step down to this destructive layer from a cornice fall or  from a storm slab being triggered.

Problems

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.