Archived

Avalanche Forecast

Mar 6th, 2019–Mar 7th, 2019

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

1: Low

The avalanche danger rating in the alpine will be low

Treeline

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

1: Low

The avalanche danger rating in the alpine will be low

Treeline

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Purcells.

Lingering wind slabs may be difficult to detect under a dusting of new snow. A persistent slab problem still exists at lower elevations and has been responsible for sporadic human-triggered avalanches.

Confidence

Moderate -

Weather Forecast

Convective snow showers on Thursday could mean that some areas receive higher than forecast snowfall amounts.WEDNESDAY NIGHT - Mainly cloudy with flurries, 2 cm / southeast winds 10-30 km/h / alpine low temperature near -10THURSDAY - Mainly cloudy with flurries, 3-5 cm. / southwest winds 15-30 km/h / alpine high temperature near -9FRIDAY - Mainly cloudy with sunny periods and isolated flurries / southwest winds 10-30 km/h / alpine high temperature near -12SATURDAY - A mix of sun and cloud / northwest winds, 10-20 km/h / alpine high temperature near -10

Avalanche Summary

On Tuesday, there were two reports of human triggered persistent slab avalanches that failed on the early February persistent weak layer (described in more detail in the Snowpack Summary). These were size 1 and 1.5, on west aspects.In recent days, there have been reports of size 1-1.5 wind slab avalanches on a variety of aspects in the alpine and at treeline, as well as size 1-1.5 loose snow avalanches, primarily on sun exposed slopes.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

Around 5 cm of snow is expected to fall on Thursday. Some convective snow showers could mean that some areas receive closer to 10 cm. The new snow will sit on wind slabs and facets (sugary snow) in most areas, and a crust on sun exposed slopes. The wind slabs may continue to be reactive as they are also sitting on facets. There are up to three layers of surface hoar (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.

Avalanche 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.

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 80 cm. These layers have evolved into a lower likelihood/high consequence avalanche problem.

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood: Unlikely

Expected Size: 1 - 2