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Avalanche Forecast

Archived

Apr 13th, 2013–Apr 14th, 2013

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

Regions

South Columbia.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Sunday: Very light snowfall / Light northeast winds / Freezing level at 1400mMonday: Mix of sun and clouds / Light east winds / Freezing level at 1400mTuesday: Mix of sun and cloud / Calm winds / Freezing level at 1600m

Avalanche Summary

Observations are becoming more limited; however a size 2 natural wind slab avalanche was observed on a lee alpine feature on Friday. A size 2 slab was also ski cut on a steep southeast facing convex roll. Surface hoar was the suspected interface.I would expect ongoing storm instabilities in the wake of new snow and wind on Friday night.

Snowpack Summary

Moderate to locally heavy snowfall on Friday night has created touchy new storm/wind slabs, especially near ridge top. This will add to existing storm slab and wind slab problems at alpine and treeline elevations. A surface hoar interface is buried within the upper metre or so of the snowpack, mainly on high-elevation northerly aspects. It may be slowly gaining some strength, but these slopes should still be treated with suspicion. On other slopes, recent storm snow overlies a crust, with a variable bond. At low elevations, moderate accumulations overlie previously rain-soaked snow which is now refrozen and strong.Recent wind and snow has added to the size and fragility of large cornices.

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.

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.