Avalanche Forecast

Issued: Mar 17th, 2014 9:50AM

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

bcorrigan, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Synopsis: A low pressure system in the Gulf of Alaska will feed moisture onto the coast for the next 4 or 5 days.Tonight: Cloudy with flurries, possible 5 to 10 cm of precipitation,, freezing level around 500 metres winds from the south light occasionally gusting to moderate.Tuesday: Cloudy with snow, 20 to possible 30 cm of precipitation, freezing level around 800 metres, winds from the south west light occasionally gusting moderate to strong.Wednesday: Cloudy with flurries, 10 to 15cm of precipitation expected, freezing level around 400 metres, ridge top winds light from the west, gusting to moderate.Thursday: Cloudy with sunny periods and possible flurries, trace amounts of precipitation, freezing level around 700 metres, winds light occasionally gusting to moderate.

Avalanche Summary

Reports of large size 2 and 3 avalanches during and after the most recent storm. Wind slab activity and explosive triggered slabs have been releasing down to the early-March layer.

Snowpack Summary

Continued precipitation and strong winds are building wind slabs in lee terrain and increasing the depth of the storm slab that overlies the March persistent weak layer. This persistent weak layer is now buried well over a metre in the north of the region and approaching a metre in the southern part of the forecast region.The March weak layer is a combination of hard wind-scoured slab surfaces in exposed terrain, facets and/or surface hoar in sheltered and north aspects, and sun crust on steep solar aspects and is widespread throughout the forecast region.A late January/early February crust/facet/surface hoar combo is still showing up in snowpack tests with moderate to hard shear tests. This layer will be with us for a long time, and a slide triggered on this layer would be very large and destructive. Recent warming temperatures will be good for bonding on this layer, but a sudden increase in load, or a large rainfall event could "wake up" this layer and result in very large avalanches.

Problems

Storm Slabs

Wind slabs continue to build on lee slopes, storm snow is sitting on a variety of older weak surfaces Steep south aspects have rain and sun crusts. Conservative terrain choices are critical. Rider triggered avalanches are definitely possible now.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 4

Persistent Slabs

The March weak layer seems to have re-awakened in some parts of the region with new snow loading and strong winds

Assess start zones carefully and use safe travel techniques.>Avoid areas with overhead hazard.>Avoid runouts where triggering slopes from below is possible.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 5

Deep Persistent Slabs

Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 18th, 2014 2:00PM