Avalanche Forecast

Issued: Feb 19th, 2014 9:54AM

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

ghelgeson, 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

Synopsis: The last of the heavy hitting storms has left the province. A quick hitting pulse racing down from the NW will cross through the region Thursday leaving some very light density snow in its convective wake. A serious eastern pacific ridge brings clearing skies this weekend. Too early to say how long its reign will last. Thursday: Freezing Level: 700m; Precip; 1/5mm - 1/8 cm; Wind: Mod, W | Strong W at ridgetop.Friday: Freezing Level: Valley Bottom; Precip: Trace; Wind: Light, NW | Mod W/NW at ridgetopSaturday: Freezing Level: Valley Bottom; Precip: Nil; Wind: Light

Avalanche Summary

An ongoing avalanche cycle continues to produce natural avalanches to size 3.5. A group of skiers triggered a size 2.5 avalanche while walking along a ridgeline in the northern potion of the region Friday. While the amount of activity is beginning to taper, large avalanches continue to be reported.

Snowpack Summary

The never ending storm has produced 60 - 120 cm of total snowfall across the region which is settling into a cohesive slab that averages a 40 - 90 cm in depth. This slab rests on a nasty persistent weak layer (Late Jan/Early Feb.) surface hoar/facet/crust combo that was formed during the month of cold clear weather. Field observations continue to report easily triggered sudden planar failures on this interface in snowpack tests. Large settlements / "whoomphs" have been reported at all elevations. Large natural avalanches have been widespread and destructive. The persistent weak layer under all the storm snow is incredibly pervasive in the region. I expect touchy conditions to remain in place longer than we're normally accustomed to. Ongoing strong winds out of the SW and W have loaded lee aspects and damaged snow at all elevations, but the effect is most prevalent at and above treeline. More strong winds in the forecast are expected only to add to this problem.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

Storm Slabs

Previously SW winds should switch to the NW Thursday. 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.>Do not travel on slopes that are exposed to cornices overhead.>Avalanches initiated in the most recent storm snow could easily step down and trigger the persistant slab.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

3 - 6

Valid until: Feb 20th, 2014 2:00PM