Avalanche Forecast

Issued: Mar 7th, 2019 4:11PM

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

kdevine, Avalanche Canada

Purcells.

Wind slabs are likely to be encountered at upper elevations and may be reactive to human triggering, especially in lee features.

Summary

Confidence

Moderate -

Weather Forecast

THURSDAY NIGHT - Mainly cloudy with isolated flurries / southwest winds 20-40 km/h / alpine low temperature near -13FRIDAY - A mix of sun and cloud with isolated flurries / southwest winds 10-25 km/h / alpine high temperature near -10SATURDAY - A mix of sun and cloud / northwest winds 10-15 km/h / alpine high temperature near -10SUNDAY - Sunny with cloudy periods / northwest winds 10-15 km/h / alpine high temperature near -8

Avalanche Summary

On Wednesday there were reports of several size 1 loose snow avalanches from steep terrain.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

Approximately 5 cm of new snow is sitting on wind slabs, facets (sugary snow) and surface hoar (feathery crystals) in most areas, and a crust on sun exposed slopes. There are up to three layers of surface hoar 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 may 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.

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.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely

Expected Size

1 - 2

Valid until: Mar 8th, 2019 2:00PM