Avalanche Forecast

Issued: Mar 25th, 2014 9:19AM

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

rbuhler, Avalanche Canada

South Columbia.

Very persistent weak layers buried deep in the snowpack remain a major concern and may 'wake-up' with the weight of the new snow. Conservative terrain selection remains crucial at this time.

Summary

Confidence

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

Weather Forecast

A low pressure system will continue to produce light precipitation on Wednesday. Unsettled conditions are expected for Thursday and Friday before the next organized system arrives on Saturday. There is currently some weather model disagreement regarding overnight freezing levels.Tues. Night: Precipitation: 8-12mm, freezing level: 500-1000m, ridgetop wind: light S-SWWednesday: Precipitation tapering off midday 2-4mm, freezing level am: 500-1000m pm: 1300m, ridgetop wind: light SWThursday: Mostly cloudy, scattered precipitation 1-3mm, freezing level am: 300-500m pm: 1000m, ridgetop wind: light SW-WFriday: Scattered precipitation 2-5mm, freezing level am: 500-800m pm: 1400m, ridgetop wind: light SW-W

Avalanche Summary

Reports from Monday include isolated natural and human triggered up to size 2. This includes soft slabs up to 30cm thick and both dry and wet sluffing from steep terrain features. In the North Columbia region, a size 4 avalanche released on a deep persistent weak layer resulting in the destruction of mature timber and 1 fatality.

Snowpack Summary

The upper snowpack may have various non-persistent weak layers within the recent storm snow. This includes small surface hoar in sheltered areas, thin sun crusts on solar aspects, rain crusts at lower elevations, and/or small facets. These layers are not widespread and are not expected to persist very long but they continue to produce small slab avalanches. Weak cornices and stubborn wind slabs may also be a concern in some areas.There are three persistent weak layers that remain a concern. The mid-March sun crust/surface hoar layer is down 50-80cm. Recent snowpack tests suggest that the reactivity of this layer is becoming more isolated but many areas still have the potential for human-triggering. The early-March crust/facet/surface hoar layer is down around 80-120cm. Human-triggering has become less likely but the layer still has the potential to produce large avalanches and we continue to see activity stepping down to this layer. The mid-February crust/facet/surface hoar layer is typically down at least 1.5m and direct triggering has become unlikely. However, large triggers like cornices or smaller avalanches can still trigger this layer and produce very large avalanches.

Problems

Storm Slabs

Weaknesses exist within or under the recent storm snow and could be triggered by the weight of a rider, especially in steep wind-loaded terrain.

Choose well supported terrain without convexities.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

The early-March and mid-March weak layers are still reactive to human-triggering and have the potential to produce large avalanches. The early-March layer is particularly tricky and conservative terrain selection remains crucial.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Minimize exposure to sun exposed slopes when the solar radiation is strong.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

The early February weak layer is still active and has produced some stunning avalanches recently. Very large avalanches may result from smaller avalanches stepping down, a cornice fall, or a rider finding the sweet spot.

Be aware of thin areas that may propogate to deeper instabilites.>Be aware of the potential for large, deep avalanches due to the presence of deeply buried weak layers.>Avoid rock outcroppings, large convexities and anywhere the snowpack is thin and/or variable.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Mar 26th, 2014 2:00PM