Avalanche Forecast

Issued: Mar 18th, 2014 9:24AM

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

bcorrigan, Avalanche Canada

South Coast.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

Synopsis: A low pressure system in the north Pacific continues to feed moisture into BC.Tonight: Cloudy with flurries, freezing level around 900 metres, winds from the south west, light to moderate occasionally gusting to strong.Wednesday: Cloudy with flurries, 10 to 20cm of precipitation expected, freezing level up to 1200 metres, ridge top winds light from the west, gusting to strong.Thursday: Cloudy with sunny periods and possible flurries, trace amounts of precipitation, freezing level around 700 metres, ridge top winds light from the west.Friday: Cloudy with sunny periods and scattered flurries. Freezing level around 1000 metres, ridge top winds light from the west.

Avalanche Summary

The Coquihalla area has just experienced a large natural avalanche cycle and the Duffey lake road saw several large explosive controlled avalanches. A rider triggered (large) size 1 was reported in the Duffey lake area on Sunday. With the forecast incoming storms, the hazard is going to be with us for a while still.

Snowpack Summary

Between 50 and 70 cm of recent storm snowstorm snow at upper elevations is sitting on a a variety of weak layers. Strong westerly winds continue to form wind slabs on lee slopes. The two persistent weak layers that remain a concern are:The March weak layer. 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 generally widespread throughout the forecast region.A late January/early February crust/facet/surface hoar combo that is still showing up in snowpack tests with 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. There are also basal facets at the bottom of the snowpack from cold clear weather in early December, but for the most part these have not been a concern. Recent large avalanches have reportedly scoured some avalanche tracks down to the basal facets and even the ground.

Problems

Storm Slabs

The last storm left us with wind slabs at tree line and above. Cornices are getting large and mature. Steep solar aspects may become active when the sun comes out on the recent storm snow.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Pay attention to overhead hazards like cornices.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

The weak layers buried deep in the snowpack may become reactive with new snow loading. Conservative terrain choices are important now.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 19th, 2014 2:00PM