Avalanche Forecast

Issued: Mar 24th, 2014 9:45AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. 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 there have been several very large, destructive avalanches in the last couple days on these layers. Conservative terrain selection remains crucial at this time.

Summary

Confidence

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

Weather Forecast

Unsettled conditions are expected for Tuesday before a frontal system arrives Tuesday evening. Precipitation is expected for Tuesday night through to Wednesday night. Unsettled conditions are expected again for Thursday. Freezing levels are expected to be higher to the south of the region and precipitation amount are expected to be higher to the north of the region.Tuesday: Light scattered flurries possible 0-2cm, freezing level am: surface pm: 800-1400m, ridgetop wind: light SE-SWTues. Night/Wednesday: Snowfall 15-25cm, freezing level am: 300-700m pm: 600-1200m, ridgetop wind: light SWThursday: Scattered flurries 2-5cm, freezing level am: surface pm: 800-1400m, ridgetop wind: light variable

Avalanche Summary

Reports from Sunday include natural and human-triggered avalanche activity up to size 1.5 within the recent storm snow, typically down 20-35cm, and natural sluffing from steep features. Early reports from Monday include a natural size 2 loose wet avalanche in the Rogers Pass area and a large slab avalanche release in the N Columbia region.

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. Also, expect some loose wet activity on solar aspects when the sun is out.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - 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.

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

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Mar 25th, 2014 2:00PM