Avalanche Forecast

Issued: Feb 20th, 2019 4:33PM

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

kdevine, Avalanche Canada

Purcells.

Though avalanche activity has slowed down, it is worth keeping in mind that the potential still exists for humans to trigger persistent slab avalanches. While these avalanches are becoming less likely, the consequences remain high.

Summary

Confidence

High -

Weather Forecast

WEDNESDAY NIGHT - Cloudy with clear periods and isolated flurries / northeast winds 10-20 km/h / alpine low temperature near -17THURSDAY - A mix of sun and cloud with isolated flurries / southeast winds 10-20 km/h / alpine high temperature near -13FRIDAY - Mainly cloudy with flurries, 5 cm / southwest winds 15-30 km/h / alpine high temperature near -13SATURDAY - A mix of sun and cloud with isolated flurries / northwest winds, 10-15 km/h / alpine high temperature near -13

Avalanche Summary

On Tuesday, one size 2 natural avalanche was reported on a southeast aspect.On Monday, there were reports of several natural and human triggered avalanches to size 2.5 on both north and south aspects at alpine and treeline elevations.On Sunday, there were reports of both natural and human triggered avalanches to size 2. Most of these were either storm slabs or wind slabs, but a few of them were persistent slabs that failed on a persistent weak layer that was buried in mid January. There is a great MIN report of a human triggered persistent slab avalanche on Sunday in the Hellroaring Creek area here.

Snowpack Summary

Depending on location, the snow surface either consists of 15-40 cm of low density snow, wind slabs, or sun crusts on steep south facing terrain. Wind slabs may be found on all aspects due to recent variable wind direction. This new snow sits on old wind slabs and/or facets (sugary snow).Lower down there are two layers of of surface hoar (feathery crystals) that were buried at the end of January and mid-January. These layers are around 30 to 70 cm deep and are most prominent at treeline and below treeline elevations. The surface hoar may sit on a crust on south facing slopes.The base of the snowpack is composed of weak and sugary faceted grains that sit on a crust. This weak layer has produced large and destructive avalanches that are sporadic in nature and very difficult to predict. It is most likely to be triggered from areas where the snowpack is shallow and weak. Rocky alpine bowls, ridge crests, and rocky outcroppings are some examples of terrain features to be wary of. See the Forecaster Blog here for more information on this problem.

Problems

Wind Slabs

Recent snow and strong wind have formed slabs at higher elevations. The most snow accumulated in the south of the region. The wind has blown from variable directions, so all aspects are suspect.

Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.If triggered, wind slabs may step down to deeper layers and result in even larger avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

Two weak layers of surface hoar are buried between 30 and 70 cm in the snowpack. The layers are most prominent around treeline and below treeline elevations.

Be aware of the potential for wide propagation.Avoid steep, open and/or sparsely treed slopes at and below treeline.Use conservative route selection, choose moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 21st, 2019 2:00PM