Avalanche Forecast

Issued: Jan 17th, 2014 8:29AM

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 Wind Slabs.

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

A ridge of high pressure will continue to dominate the region bringing dry conditions and mainly clear skies for the foreseeable future. Winds should be light to moderate from the west on Saturday, becoming light and northwesterly on Sunday and Monday. An inversion is expected for Saturday bringing valley cloud and alpine temperatures reaching +5.0. More seasonal temperatures are expected for Sunday and Monday.

Avalanche Summary

Several large and very large natural and explosive-triggered slab avalanches were observed in the region over the past week. Many of the avalanches started within the recent storm snow, and then stepped down to basal facets at ground level. In at least 2 reported 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

Last week's snowfall amounts were highly variable throughout the forecast area, with the western parts of the range getting as much as 90cm. Strong to extreme winds pounded the storm accumulations into hard wind slabs in most areas. The recent storm 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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 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.

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

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Wind Slabs

Hard wind slabs exists in many areas throughout the region. Although they have gained considerable strength, triggering is possible in unsupported terrain, on sun-exposed slopes, or in areas where they overlie persistent weaknesses.

Be aware of the potential for wide propagations due to the presence of hard windslabs.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

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