Avalanche Forecast

Issued: Jan 22nd, 2019 4:07PM

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.

swerner, Avalanche Canada

Purcells.

Choose conservative terrain and dont be connected to large overhead slopes. Steep, rocky slopes with a variable thin to thick snowpack are susceptible to human triggers, resulting in large destructive avalanches.

Summary

Confidence

High -

Weather Forecast

Tuesday Night: Cloudy with a trace of new snow. Ridgetop winds light from the southwest and alpine temperatures near -9. Freezing levels at valley bottom.Wednesday: Mix of sun and cloud. Ridgetop winds moderate from the West and alpine temperatures near -8. Freezing levels 1200 m. Thursday: Cloudy with sunny periods. Ridgetop winds moderate from the West and freezing levels near 800 m. Friday: Mix of sun and cloud. Ridgetop winds light from the northwest and alpine temperatures near -6. Freezing levels rise to 1100 m.

Avalanche Summary

On Monday, several skier triggered wind slabs up to size 2 were reported. These were mostly on N-NE aspects above 2300 m. At this point there isn't much snow overlying the weak layers in the upper snowpack, however, these layers wont be going anywhere fast and just need more load above them to initiate avalanches. Given the weak nature of the snowpack, the main concern remains the possibility for triggering large deep persistent slab avalanches. Large and very large (size 2.5-3.5) avalanches have been reported regularly over the past few weeks.

Snowpack Summary

Up to 20 cm of recent snow has buried large surface hoar crystals and/or sun crusts. This will likely develop into a touchy problem as more snow accumulates. The most suspect terrain features will be steep slopes and rolls between 1500m- 2000 m (where the largest surface hoar exists) and steep south-facing slopes in the alpine (where sun crust exists). Reactive wind slabs can also be found at upper elevations on lee (N-NE) slopes. The weak nature of the snowpack lies at depth. The base of the snowpack is composed of weak faceted grains and a crust in many parts of the region. People have and will continue to be able to trigger these layers in areas where the snowpack is shallow. These areas typically include ridgelines, large open slopes and bowls at upper elevations. Common trigger points are rocks, trees and areas where the snowpack is variable (thin to thick and variable).

Problems

Deep Persistent Slabs

Large destructive avalanches have consistently been triggered on deeply buried weak layers. This problem will exist for a while to come and is tricky to manage. Likely trigger points are shallow snowpack areas, such as near ridges and rocky terrain.

Choose supported, conservative terrain and don't be connected to large overhead slopes.Avoid steep slopes and areas with a thin, variable snowpack.Watch for signs of instability such as whumpfing, cracking, or recent avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

10-20 cm of recent snow amounts have accumulated above the previous surface of weak surface hoar and crusts. Wind loaded slopes now have enough snow above this layer for small avalanches.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered, slabs may step down to deeper layers resulting in large avalanches.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 1.5

Valid until: Jan 23rd, 2019 2:00PM