Avalanche Forecast

Issued: Jan 23rd, 2019 4:17PM

The alpine rating is moderate, 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 avoid being connected to large overhead slopes. Steep, rocky slopes with a variable thin to thick snowpack like ridgelines and open alpine bowls are more susceptible to human triggers.

Summary

Confidence

High -

Weather Forecast

Thursday: Mix of sun and cloud gusty westerly ridgetop winds. Alpine temperatures near -6 and freezing levels rising to 700 m.Friday: Mix of sun and cloud with moderate westerly ridgetop winds. Alpine temperatures high of -5 and freezing levels 1000 m. Saturday: Mix of sun and cloud with light to moderate westerly ridgetop winds. Alpine temperatures high of 0 degrees and freezing levels rising to 2500 m.

Avalanche Summary

No new avalanches reported on Tuesday. There is a MIN report that shows another deep persistent natural slab avalanche size 3.5 that happened last Saturday in International Basin. It may have been triggered by a wind event. Even though the weather pattern is fairly benign the deep persistent basal facet/ crust lingers just waiting for a weather event or a human trigger.Check out the MIN here.

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 in areas where a cohesive slab sits above the weak interface. The most suspect terrain features will be steep slopes and rolls between 1500 m- 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). If you trigger a deep persistent slab it will go big and be a destructive avalanche.

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

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 the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Jan 24th, 2019 2:00PM