Avalanche Forecast

Issued: Feb 17th, 2018 5:35PM

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

shorton, Avalanche Canada

Kootenay Boundary.

Fresh storm slabs will be reactive to human-triggers, especially in wind-affected terrain. Watch for signs of unstable snow such as whumpfs and cracks.

Summary

Confidence

Moderate -

Weather Forecast

SUNDAY: Lingering flurries in the morning with 3-8 cm of new snow followed by clearing and cooling as Arctic air pushed into the region, moderate northeast wind, alpine high temperatures around -18 C.MONDAY: Mix of sun and cloud, light northeast wind, alpine high temperatures around -18 C.TUESDAY: Mix of sun and cloud, light north wind, alpine high temperatures around -18 C.

Avalanche Summary

On Saturday, widespread natural avalanche activity was reported. Storm slabs were generally soft and thin (20-30 cm), but had wide propagations and ran far distances. Ski cutting and explosives produced similar avalanches. Similar activity in the storm snow was also reported on Friday.Last weekend, three large persistent slab avalanches (size 3) were reported on northeast aspects in the Valhallas. Two were triggered with explosive and the third was naturally triggered. Natural activity on deeply buried weak layers has wound down, but human triggering remains a concern.

Snowpack Summary

Saturday's storm delivered 20-40 cm of low density snow, except for pockets with soft slabs in exposed terrain. A total of 30-50 cm of snow sits above an interface that could favour wide propagations once the snow settles. The interfaces include sun crusts on steep south-facing slopes, a rain crust below 1800 m and small surface hoar in isolated areas.We now have 1-2 m of settled snow sitting on three significant surface hoar/crust layers that were formed early to mid-January, and back in December. Near the base of the snowpack a crust/facet interface exists that will likely haunt us all season. These layers produced large destructive avalanches on a regular basis up until last weekend. Avalanche activity on these layers has gradually diminished, but the persistent slab problem still demands respect and diligence.

Problems

Storm Slabs

New snow is forming touchy slabs, especially in wind-affected terrain at higher elevations. Watch for areas where the snow has settled into a stiff slab.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

Several deeply buried weak layers exist in the snowpack. Although the likelihood of triggering a persistent slab is gradually decreasing, the consequences remain very high.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Caution around convexities or areas with a thin or variable snowpack.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2.5 - 4

Valid until: Feb 18th, 2018 2:00PM