Avalanche Forecast

Issued: Jan 25th, 2019 3:13PM

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

jfloyer, Avalanche Canada

Purcells.

Anticipated warming could potentially wake up lower weak layers resulting in the potential for large human-triggered avalanches.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Lt Dragon (2380m):Nil; TPres -4, rising rapidly; TMin -10; winds L NWToby Ck (1130m):1cm; TPres -1 rising rapidly; TMin -13KHMR Dogtooth (2060m):Nil; TPres -7, rising slowly; TMin -10KHMR Top (2325m):Winds 20-40 W

Avalanche Summary

One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. On Thursday, explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a MIN report from last Saturday that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check out the MIN here. Dealing with the deep persistent basal facet/crust problem requires avoiding terrain where this kind of avalanche is possible.

Snowpack Summary

Up to 20 cm of recent snow has buried large surface hoar crystals which, on southern aspects, may rest on a sun crust. In most places, there is still insufficient snow over this layer and the upper snow too unconsolidated to create a widespread problem. However, locally, in deeper snowpack areas, or where the wind has blown snow above this layer, avalanches large enough to be of concern could be triggered. The snowpack also has a significant weekness at depth. The base of the snowpack is composed of weak faceted grains and a crust in many parts of the region. There have been sporadic reports of people triggering this layer in areas where the snowpack is shallow. The most likely trigger points include ridgelines and large open slopes and bowls at upper elevations, particularly those that have rocky or variable (thin to thick) features. If you trigger a deep persistent slab it will go big and be a highly destructive avalanche.

Problems

Deep Persistent Slabs

Large destructive avalanches have consistently been triggered on deeply buried weak layers. This problem will exist for a while to come and is tricky to manage. Likely trigger points are shallow snowpack areas, such as near ridges and rocky terrain.

Watch for signs of instability such as whumpfing, cracking, or recent avalanches.Avoid steep slopes and areas with a thin, variable snowpack.Choose supported, conservative terrain and don't be connected to large overhead slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

Wind slabs should be treated with caution in exposed areas, particularly as triggering something on the surface could step down to the deep persistent layer below.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 26th, 2019 2:00PM