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Avalanche Forecast

Archived

Mar 30th, 2015–Mar 31st, 2015

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

Regions

Sea To Sky.

Large and destructive avalanches will remain a concern long after the stormy weather has ended. See this blog post for additional info: http://bit.ly/1HHQrK2

Confidence

Fair - Due to the number of field observations

Weather Forecast

A general cooling pattern is expected for the forecast period. On Tuesday, Wednesday and Thursday only trace amounts of new snow are expected each day with the possibility of occasional sunny breaks. Ridgetop winds should remain light to moderate from the northwest with daytime freezing levels hovering at about 1300m

Avalanche Summary

We have not yet heard how avalanche activity panned out in response to the recent storms, due to limited visibility and the challenges of backcountry travel at this time. We have previously had ongoing reports of very large slab avalanches running on the mid-March persistent weak layer. I would be very surprised if this layer has not performed during the recent storm cycle.

Snowpack Summary

This region is dealing with a very serious persistent slab problem that is currently being subjected to significant additional loading by new snow and/or rain. Depending on how much recent snow has fallen, a facet/crust persistent weak layer buried mid-March lies anywhere from 50-150 cm below the surface. This interface has been incredibly volatile recently and remains sensitive to both human and natural triggering, especially where the slab is thinner. Recent compression tests have produced sudden planar failures at this interface. At lower elevations, rain has saturated the snowpack. Layers below the critical mid-March interface are generally considered to be well-settled and strong.

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.

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.