Avalanche Forecast

Issued: Jan 16th, 2019 4:30PM

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

shorton, Avalanche Canada

Purcells.

Triggering large avalanches remains a serious concern in the Purcells. Read more here in the Forecaster's Blog.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

WEDNESDAY NIGHT: Cloudy with clear periods, light wind, alpine temperatures drop to -10 C.THURSDAY: Isolated flurries with up to 5 cm of snow, light southeast wind, alpine high temperatures around -8 C.FRIDAY: Mostly cloudy with isolated flurries, light southwest wind, alpine high temperatures around -6 C.SATURDAY: 5-10 cm of snow, moderate to strong southwest wind, alpine high temperatures around -6 C.

Avalanche Summary

The likelihood of triggering large avalanches is still 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.On Wednesday, a large (size 3) naturally triggered avalanche was observed on a southeast aspect in the alpine near Golden.On Monday, several large (size 2) avalanches were observed throughout the region, some releasing on weak faceted grains near the base of the snowpack.On Sunday, a large (size 3) avalanche ran full-path on a southwest aspect in the alpine near Golden.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.Last Friday, five large to very large (size 2 to 3.5) deep persistent slab avalanches were observed on various aspects in alpine terrain.

Snowpack Summary

The snowpack is weak and touchy in large portions of the Purcells. Numerous very large avalanches have been reported on a regular basis. This is the type of weak snowpack that could stick around for months. Read more here. Recent sunshine and warm alpine temperatures left crusty surfaces on solar aspects while the snow appears to have remained dry on shady 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 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.Best to avoid steep slopes and areas with a thin, variable snowpack. Avoid overhead exposure.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

Wind slabs may linger at higher elevations. The real danger is if a small slab stepped down to the lower weak layer.

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.

Aspects: North, North East, East, West, North West.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Jan 17th, 2019 2:00PM