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Avalanche Forecast

Archived

Mar 29th, 2015–Mar 30th, 2015

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

Regions

Sea To Sky.

Don't underestimate the avalanche danger at this time. Forecast new snow and rain could overload a significant weak layer with the potential to release very large avalanches. See this blog post for additional info: http://bit.ly/1HHQrK2

Confidence

Good

Weather Forecast

Storms on Monday and Monday night are expected to taper off Tuesday, although some lingering showers are likely in their wake. Monday: 10-20 mm precipitation is expected during the day, with a further 15-25 mm overnight between 4pm Monday and 4am Tuesday. Freezing levels during the day on Monday will rise to around 1900 m and ridgetop winds will be around 60 km/h from the southwest. Tuesday: Residual showers may occasionally be heavy for short durations. Freezing levels lowering to around 1000 m, winds diminishing to around 35 km/h from the west. Wednesday: Mostly dry with the occasional shower. Freezing levels remaining around 1000 m and winds light northwesterly.

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.