Avalanche Forecast

Issued: Feb 22nd, 2014 8:24AM

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

rbuhler, Avalanche Canada

Purcells.

Conditions are very tricky and prime for human-triggered avalanches. See this blog post for advice on managing the problem. The hazard will increase on south facing slopes on the first day of full sun.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Unsettled conditions are expected for Sunday as weak system crosses the south of the province before an Arctic ridge of high pressure pushes into the region late-Sunday/early-Monday. Clear, cold, and dry conditions will dominate conditions for most of the week.Sat. Night/Sunday: Partly cloudy, scattered flurries 1-3cm, treeline temperatures around -15C, ridgetop winds light SW-NWMonday/Tuesday: Clear and sunny, treeline temperatures around -12, ridgetop winds light NW-NE

Avalanche Summary

Natural avalanche activity is generally decreasing now that the storm has ended but we are still receiving reports of natural activity. Conditions are ideal for human triggering right now and we have received numerous reports of skier triggered avalanches, many of which have released quite deep in the snowpack. Several of these avalanches were remotely triggered. On Friday, we had a report of a size 2.5 skier remote avalanche the released 150cm deep and was triggered from 60m away.Â Explosive control produced size 3 avalanches with the deepest stepping down 2m and the longest running 900m.

Snowpack Summary

The recent ten-day storm has produced 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 preceding month of cold, dry weather. This weak layer is widespread at all elevations and aspects, and is creating problems even in previously skied terrain. Large settlements and whumpfs have been reported at all elevations. We have received numerous reports of remotely-triggered avalanches from as far as 500m away which indicates a high likelihood of large propagations within the weak layer. 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

A thick slab from the last series of storms sits on top of a touchy persistent weak layer and remains primed for human triggering. This meter deep slab has shown a propensity for remote triggering. In wind-loaded areas the slab is up to 2m thick.

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

Likely

Expected Size

2 - 6

Wind Slabs

Recent storm snow is being redistributed as wind slabs on lee terrain features. Primary wind directions have recently been SW through NW. Weak cornices are also a concern and have the potential to trigger large avalanches on the slopes below.

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 - Very Likely

Expected Size

1 - 4

Valid until: Feb 23rd, 2014 2:00PM