Avalanche Forecast

Issued: Mar 29th, 2015 8:47AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is moderate. Known problems include Persistent Slabs and Storm Slabs.

jfloyer, Avalanche Canada

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

Summary

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

There is significant danger that a touchy persistent weak layer buried an average of a metre below the surface will become overloaded by new snow and rain. Because it is deeply buried, particularly large and destructive avalanches are expected.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Remote triggering is a concern, watch out for adjacent slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

3 - 7

Storm Slabs

An active weather pattern is expected to develop new storm slabs on all aspects above around 1800 m. These will be especially touchy where they are drifted into fat pillows by the wind.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Be aware of what is above you at all times.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Valid until: Mar 30th, 2015 2:00PM