Avalanche Forecast

Issued: Feb 24th, 2019 4:13PM

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

jsmith, Avalanche Canada

Purcells.

A persistent weak layer that has been most pronounced at lower elevations has created a low likelihood, high consequence scenario that requires discipline and careful terrain selection to manage effectively.

Summary

Confidence

High - The weather pattern is stable

Weather Forecast

SUNDAY NIGHT: Clear / Light, northeasterly winds / Alpine low -19.MONDAY: Sunny / Light, northeasterly winds / Alpine high -17.TUESDAY: Sunny / Light, northeasterly winds / Alpine high -15.WEDNESDAY: Sunny / Light, northeasterly winds / Alpine high -8.

Avalanche Summary

On Saturday there was a report of a skier triggered size 2 persistent slab avalanche 30-50 cm deep on a northeast aspect in the Dogtooth range. This person was seriously injured after being swept over a 30 m cliff and carried by the avalanche for a total of 650 m. On Thursday and Friday a few reports of natural and skier triggered wind slab avalanches to size 1 in the alpine. On Thursday, there was a report of a human triggered persistent slab avalanche, size 1.5. On Wednesday there was a report of a human triggered size 2 persistent slab avalanche in the Gorman Lake area. There is a great MIN report detailing this avalanche here.Most days this week there have been reports of persistent slab avalanches. These avalanches are becoming fewer and further between, but they are still being triggered by people and carry a high consequence.

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. 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 80 cm deep and are most prominent at treeline and below. 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. See the Forecaster Blog here for more information on this problem.

Problems

Persistent Slabs

Two weak layers of surface hoar are buried between 30 and 70 cm in the snowpack.

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

Wind Slabs

Buried wind slabs that are sitting on facets (weak, sugary snow) in rocky alpine terrain may remain reactive to human triggers.

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.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

The base of the snowpack is composed of weak faceted grains and a crust, particularly in thin snowpack areas. This layer has produced sporadic but very large avalanches. The probability of triggering this layer is low, but the consequences very high.

Use caution on alpine slopes, especially around thin snowpack areas.Minimize overhead exposure; avalanches triggered by cornice fall may be large and destructive.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2.5 - 3.5

Valid until: Feb 25th, 2019 2:00PM