Avalanche Forecast

Issued: Jan 16th, 2014 8:55AM

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

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure continues to dominate most of the province bringing mainly clear skies for the forecast period. Winds are expected to be light to moderate from the northwest, becoming westerly on Sunday. Alpine temperatures should hover between 0.0 and +5.0 on Friday and Saturday with some cooling expected for Sunday.

Avalanche Summary

Several large and very large natural and explosive-triggered slab avalanches were observed in the region over the past few days. Many of the avalanches started within the recent storm snow, and then stepped down to basal facets at ground level. In at least reported 2 cases, natural cornice fall was the trigger. One report included a size 4 avalanche in the Jumbo area which took out 5 ha of mature trees, up to 100yrs old,Forecast warm temperatures will increase the likelihood of continued deep slab activity.

Snowpack Summary

Recent snowfall amounts were highly variable throughout the forecast area, with the western parts of the range getting as much as 90cm in the past week. The new snow sits on a variety of snow surfaces including older wind slab, a soft layer of facetted snow and/or surface hoar buried in early January.In the mid pack you may find a surface hoar layer buried in mid December. Further down you may also find the December facet/crust combo. Both interfaces give variable results in snowpack tests, but professional operators are treating them with caution.The biggest concern throughout the region is a layer of weak sugary depth hoar at the base of the snowpack. These crystals may coexist with a crust which formed in October. Several large avalanches in the past few weeks have been attributed to failures at this layer. Wide propagations on relatively gentle terrain have been noted, and an alarming tendency for seemingly disconnected slopes to propagate over a wide area and produce large avalanches. Forecast warm temperatures will increase the likelihood of continued avalanche activity at this interface

Problems

Deep Persistent Slabs

Several deep and destructive avalanches have failed at ground level over the past few weeks. Forecast warming will promote ongoing activity at this interface with the potential for very large avalanches.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>Caution around convexities or areas with a thin or variable snowpack.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 7

Loose Wet

Forecast warming will likely produce loose wet avalanches in steep, sun-exposed terrain. A loose wet avalanche in motion may also "step down" triggering deep and destructive slab avalanches.

Sluffs may trigger deeper instabilities.>Avoid exposure to solar aspects overhead, large avalanches may reach the end of run out zones.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Storm Slabs

Recent storm slabs have most likely gained strength. Triggering may be more likely on steep terrain where the new snow exists as a wind slab, where it overlies recently buried surface hoar, or on sun-exposed slopes.

Dig down to find and test weak layers before committing to a line.>Be cautious as you transition into wind affected terrain.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Jan 17th, 2014 2:00PM