Avalanche Forecast

Issued: Mar 5th, 2019 4:47PM

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

kdevine, Avalanche Canada

Purcells.

Wind slabs continue to be reactive at upper elevations. A persistent slab problem still exists at lower elevations and has been responsible for occasional human-triggered avalanches.

Summary

Confidence

Moderate -

Weather Forecast

TUESDAY NIGHT - Clear periods / southeast winds 10-30 km/h / alpine low temperature near -12WEDNESDAY - Cloudy with sunny periods and isolated flurries / southeast winds 10-25 km/h / alpine high temperature near -10THURSDAY - Mainly cloudy with flurries, 5 cm / southwest winds 10-30 km/h / alpine high temperature near -8FRIDAY - Cloudy with isolated flurries / west winds, 15-30 km/h / alpine high temperature near -9

Avalanche Summary

On Monday, there were reports of a few human triggered avalanches, size 1-1.5. These were mainly wind slab avalanches, but there were two reports of persistent slab avalanches in the southwest of the region that failed on the persistent weak layer that was buried in early February.Here is a link to a video of an avalanche that occurred last week in the Purcells that illustrates the current wind slab problem in the region.Reports of persistent slab avalanches are becoming less frequent, suggesting our January/February weak layers have evolved into a lower likelihood/high consequence avalanche problem that still requires a measure of discipline to manage effectively.

Snowpack Summary

In most areas, the surface is primarily wind slabs, and a crust on sun exposed slopes. The wind slabs continue to be reactive, likely due to the fact that they are sitting on facets (sugary snow).Up to 25 cm of snow fell at the end of last week in the southwest of the region. This snow likely sits on wind slabs, and a crust on sun-exposed aspects. The snow surface is likely a crust on sun exposed slopes.Lower down there are up to three layers of surface hoar (weak, feathery crystals) that were buried in mid and late January, and early February. These layers are around 30 to 80 cm deep and are most prominent at lower elevations - especially below treeline. 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 difficult to predict. See the Forecasters' Blog here for more information on this problem. Continued cold temperatures have been weakening the lower snowpack.

Problems

Wind Slabs

Wind slabs can be found on all aspects and continue to be reactive due to the weak, faceted snow they sit on.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Steep and rocky terrain are likely places to trigger buried wind slabs.Exercise increased caution around freshly wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Persistent Slabs

Three weak layers of surface hoar are buried between 30 and 70 cm down in the snowpack. These layers have evolved into a lower likelihood/high consequence avalanche problem.

Maintain diligent group management around steep, sparsely treed slopes at treeline and below.Exercise increased caution around low elevation cut-blocks where this layer is well preserved.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely

Expected Size

1 - 2

Valid until: Mar 6th, 2019 2:00PM