Avalanche Forecast

Issued: Feb 20th, 2014 9:16AM

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

rbuhler, Avalanche Canada

Purcells.

We're moving from a storm slab problem to a persistent slab problem. Check out this blog post for thoughts on the current situation and strategies for the next the chapter.

Summary

Confidence

Fair

Weather Forecast

Unsettled conditions are expected for the next three days as the storm conditions end and a ridge of high pressure begins to build. A very weak system from the coast may affect the interior regions on Sunday. Friday: A mix of sun and cloud, scattered flurries 1-3cm, treeline temperatures around -10C, ridgetop winds 15-25km/h NWSaturday: A mix of sun and cloud, mainly dry conditions, treeline temperatures around -12C, ridgetop winds light variableSunday: Cloudy with sunny breaks, scattered flurries possible 0-2cm, treeline temperatures around -15C, ridgetop winds light variable

Avalanche Summary

Widespread natural and human-triggered avalanche activity up to size 3 was reported on Wednesday. The common theme is deep releases with many of the avalanches having a slab thickness of 80-150cm. From limited reports, natural activity appears to have reduced substantially on Thursday. One size 2.5 skier controlled avalanche was triggered by kicking a cornice onto a slope which subsequently triggered the avalanche.Â The peak of the natural cycle may be over but conditions for human triggering are prime and consequences remain high.

Snowpack Summary

The never ending storm cycle has produced 60-120 cm of total snowfall across the region which is settling into a cohesive slab that averages 40-90 cm in thickness. This slab sits on a nasty persistent weak layer surface hoar/facet/crust combo that was formed during the month of cold dry weather. Field observers continue to report easily triggered sudden planar failures on this interface in snowpack tests. Large settlements and whumpfs have been reported at all elevations, even in previously skied terrain. Large natural avalanches have been widespread and destructive. We expect touchy conditions to remain in place longer than we're normally accustomed to. Recent strong winds out of the SW through NW have created wind slabs on leeward features in wind exposed areas at treeline and in the alpine. In many areas, thick wind slabs may overlie the persistent weak layer creating conditions for very large avalanches.Weak basal facets exist in some areas, but triggering has now become unlikely. For the most part, the mid and lower snowpack are strong and well consolidated

Problems

Persistent Slabs

This problem is surprising very experienced professionals and remains primed for human triggering. This meter deep slab has shown a propensity for remote triggering, a phenomenon that should become more prevalent as the slab gains cohesion.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Use very conservative route selection, stick to simple well supported terrain that is low consequence and free of overhead hazard.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 6

Storm Slabs

Winds during the recent storms have been SW through NW. With plenty of new storm snow available for transport, fresh sensitive wind slabs will add even more complexity to an already tricky situation on wind exposed terrain features.

Avoid freshly wind loaded features.>Minimize overhead exposure; avalanches triggered by windloading may reach run out zones.>Travel on ridgetops to avoid wind slabs on slopes below.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Feb 21st, 2014 2:00PM