Avalanche Forecast

Issued: Mar 1st, 2019 4:51PM

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.

cgarritty, Avalanche Canada

Purcells.

Variable new snow amounts now blanket our wind slab problems. Keep recent wind loading patterns in mind, even if you're traveling through low density new snow.

Summary

Confidence

High -

Weather Forecast

Friday night: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Light variable winds.Saturday: Sunny with cloudy periods. Light east winds. Alpine high temperatures around -22.Sunday: Sunny. Light northeast winds. Alpine high temperatures around -17. Monday: Sunny. Light northeast winds. Alpine high temperatures around -13.

Avalanche Summary

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

Recently formed wind slabs can be found primarily on southwest aspects. Below them, hard, buried wind slabs on all aspects have continued to surprise riders. Thin to thick rocky areas are likely places to trigger these.

Steep and rocky terrain are likely places to trigger buried wind slabs.Be aware of greater new snow amounts and a touchier wind slab problem in the southwest of the regionAvoid freshly wind-loaded features, especially near ridge crests and in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

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 are slow to change and have created a low likelihood, high consequence avalanche problem in the snowpack.

Use conservative route selection, choose moderate angled terrain with low consequence.Avoid steep, open and/or sparsely treed slopes at and below treeline.Avoid low elevation cut-blocks where this layer is well preserved.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Mar 2nd, 2019 2:00PM