Avalanche Forecast

Issued: Mar 2nd, 2019 4:48PM

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

cgarritty, Avalanche Canada

Purcells.

New wind slabs, buried wind slabs, and lingering persistent slabs are maintaining a complex mix of avalanche problems. Be mindful of how this mix changes by elevation. Expect to find touchier surface instabilities in the southwest of the region.

Summary

Confidence

High -

Weather Forecast

Saturday night: Clear with cloudy periods. Light northeast winds.Sunday: Sunny. Light northeast winds. Alpine high temperatures around -17.Monday: Sunny. Light northeast winds. Alpine high temperatures around -12.Tuesday: Sunny with cloud increasing in the evening. Light east winds. Alpine high temperatures around -9.

Avalanche Summary

Observations from Friday included several storm slab releases to size 1.5 in an area of the southwest of the region that saw 25 cm of new snow from localized convective snowfall. Loose dry releases to size 1 were also observed, owing to the low density character of the new snow. On Wednesday, numerous natural wind slab avalanches up to size 2 and several human triggered size 1-1.5 releases were reported on primarily south aspects at treeline and above. Here is a link to a video of an avalanche that apparently occurred a few days ago in the Purcells. Great footage that illustrates the current wind slab problem in the region.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. Reports of persistent slab avalanches are becoming less frequent which is creating a low likelihood, high consequence scenario in the snowpack that requires discipline and careful terrain selection to manage effectively.

Snowpack Summary

Limited areas of the region received up to 25 cm of new snow on Thursday. This likely overlies sun crust on solar aspects. Below the variable cover of new snow, Recent strong northeasterly ridge-top winds have created wind slabs on lee features at treeline and above. Below this wind affected layer, older buried wind slabs exist on a variety of aspects. These remain a concern for overlying facets (weak, sugary snow), causing them to remain reactive for longer than is typical for a wind slab problem.Lower down there are two layers of surface hoar (weak, 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 lower treeline and below. The surface hoar may sit on a crust on south facing slopes in specific locations, which is a dangerous combination.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 difficult to predict. See the Forecasters' Blog here for more information on this problem.

Problems

Wind Slabs

Recent wind slabs can be found on all aspects and new snow is available to redistribute into fresh slabs in the south of the region. Below any newer slabs, hard, buried wind slabs have remained reactive due to the weak, faceted snow they sit on.

Avoid freshly wind-loaded features, especially near ridge crests and in steep terrain.Forecast northeast winds will focus new slab formation on southwest aspects.Steep and rocky terrain are likely places to trigger buried wind slabs.

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 down in the snowpack. These layers have been slow to heal and have evolved into a low likelihood, high consequence avalanche problem focused at lower elevations.

Avoid low elevation cut-blocks where this layer is well preserved.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

Unlikely - Possible

Expected Size

1.5 - 2.5

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: Mar 3rd, 2019 2:00PM