Avalanche Forecast

Issued: Jan 24th, 2019 3:36PM

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.

jfloyer, Avalanche Canada

Purcells.

Continue to select conservative terrain to avoid being caught in a deep persistent slab avalanche. Expected warming this weekend will increase the chance of a large avalanche.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

THURSDAY NIGHT: Dry. Moderate northwesterly winds.FRIDAY: Dry with clear spells. Rapidly warming temperatures with freezing levels rising to 1800 m by the afternoon. Light northwesterly winds. SATURDAY: Dry with a mix of sun and cloud. Freezing levels continuing to climb as high as 2500 m. Light northwesterly winds.SUNDAY: Light precipitation falling as rain up to around 1500 m and snow above that. 2-4 mm/cm expected. Strong westerly winds.

Avalanche Summary

One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. There is a MIN report that shows a deep persistent natural slab avalanche size 3.5 that happened last Saturday in International Basin. It may have been triggered by a wind event. Dealing with the deep persistent basal facet/crust problem requires avoiding terrain where this kind of avalanche is possible.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 are 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 have also been noted at upper elevations on lee (N-NE) slopes. The snowpack also has a significant weekness at depth. The base of the snowpack is composed of weak faceted grains and a crust in many parts of the region. There have been sporadic reports of people triggering this layer in areas where the snowpack is shallow. The most likely trigger points include ridgelines and large open slopes and bowls at upper elevations, particularly those that have rocky or variable (thin to thick) features. If you trigger a deep persistent slab it will go big and be a highly 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.

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: 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. In steep alpine terrain, there is the possibility of a small wind slab avalanche triggering the deep persistent layer below.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Jan 25th, 2019 2:00PM