Avalanche Forecast

Issued: Jan 14th, 2019 4:29PM

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

mconlan, Avalanche Canada

Purcells.

People have recently triggered large avalanches within the weak Purcells snowpack. See more in the Forecaster's Blog here. We highly suggest adopting a conservative approach to route selection.

Summary

Confidence

High -

Weather Forecast

MONDAY NIGHT: Clear skies, inversion conditions with above-freezing layer between 2200 m and 3000 m for most of the region.TUESDAY: Clear skies, light southeast winds, alpine temperature -2 C, freezing level below valley bottom.WEDNESDAY: Mix of sun and cloud, light southwest winds, alpine temperature -6 C, freezing level below valley bottom.THURSDAY: Cloudy with light snowfall, light south winds, alpine temperature -10 C, freezing level below valley bottom.

Avalanche Summary

On Monday, three more large avalanches were observed near Golden and Invermere. They released on the layer of weak faceted grains near the base of the snowpack described in the Snowpack Summary.On Sunday, there was a report of a large (size 3) avalanche that ran full-path near Golden. It released on the layer of weak faceted grains near the base of the snowpack. It was on a southwest aspect in the alpine.On Saturday, a group of snowmobilers triggered a fatal avalanche near Invermere, also on the basal weak faceted grains. The avalanche was on a southerly aspect and ran approximately 900 to 1100 m. Two snowmobilers were caught. See here for more information.On Friday, five large to very large (size 2 to 3.5) deep persistent slab avalanches were observed. They were triggered naturally, by skiers, and by explosives in alpine terrain. They released on variable aspects.The likelihood of triggering large avalanches is elevated due to the weak nature of the snowpack. Watch out in thin snowpack areas, where the likelihood of triggering deeper layers is the highest. Check out a few of the other recent large and destructive avalanches triggered by people via MIN posts here and here.

Snowpack Summary

The snowpack is weak and touchy in a large portion of the Purcells. Numerous very large avalanches have been reported daily. This is the type of weak snowpack that could stick around for months or longer.At the top of the snowpack, recent warm air and sunny skies may have produced a crust on the snow surface. Expect to find a sun crust on southerly aspects and possibly a temperature crust on other aspects. At higher elevations in exposed terrain, wind slabs may still exist.The weak nature of the snowpack lies at depth. There is a weak layer around 80 to 120 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack is also composed of weak faceted grains in many parts of the region. Humans have and will continue to be able to trigger these layers in areas where the snowpack is shallow.

Problems

Deep Persistent Slabs

People have recently triggered destructive avalanches on buried weak layers. This problem will exist for a while to come. These layers are more easily triggered by people in areas where the snowpack is shallow, such as near ridges and rocky terrain.

Observe for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches.Be aware of the potential for full-depth avalanches due to weak layers at the base of the snowpack.Best to avoid steep slopes and areas with a thin, variable snowpack. Avoid overhead exposure.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Wind Slabs

Wind slabs may linger in exposed terrain. Sunny skies may further weaken the snow on southerly aspects. Travel conservatively at higher elevations.

If triggered, slabs may step down to deeper layers resulting in large avalanches.Use caution in lee and cross-loaded terrain. Recent wind-loading has created wind slabs.Minimize exposure to steep slopes on warm or sunny days.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 15th, 2019 2:00PM