Avalanche Forecast

Issued: Jan 1st, 2017 3:52PM

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

istorm, Avalanche Canada

Northwest Coastal.

Christmas surface hoar layer is a present that keeps on giving into the New Year! Conservative terrain selection remains important.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Monday: strong northerly winds continue / warming trend starting / mix of sun & cloud / dryTuesday: moderate to strong northerly winds / slow warming trend continues / some sun & dryWednesday: light winds / warm temperatures with near zero possible close to treeline elevations / clear & dry.

Avalanche Summary

In recent days, several persistent slab avalanches to size 2 were triggered remotely or under light loads in the Terrace backcountry on a layer of surface hoar buried 30-60 cm below the surface. Many of these avalanches failed in low angle terrain. Check out the latest Mountain Information Network posts as well as the ACMG Mountain Conditions Report (mountainconditions.com) for some great reports of related avalanche activity. Information from Dec 31 shows this touchy problem remains and is likely to continue. Strong Northerly winds and rapid reverse loading led to a natural avalanche cycle on Dec 30 near Ningunsaw. I suspect this may illustrate a region wide wind slab problem.

Snowpack Summary

Recent storms deposited 50-80 cm of snow combined with strong winds, most recently from the north. The storm snow overlies a layer of feathery surface hoar (up to 15 mm in sheltered areas) buried on December 25, making wide propagations possible. Ongoing reports indicate this combination of layers is susceptible to easily triggered avalanches, including avalanches running in low angled terrain. An earlier (and therefore deeper) weak interface that formed during the early December cold snap can be found in isolated areas buried 100-150 cm deep. The layer consists of preserved surface hoar or weak faceted (sugary) snow. The lower snowpack is well consolidated in deep snowpack areas. In shallow snowpack areas, especially north of Ningunsaw, an old rain crust near the bottom of the snowpack has developed weak facets and might be triggerable from a thin or rocky area on a convex slope.

Problems

Persistent Slabs

A recently buried surface hoar layer is highly sensitive to human triggering and has given a few people a scare in the Terrace area. Forecast extreme winds may press and add cohesion to the slab promoting wider propagations.

Be aware of the potential for large avalanches due to the presence of buried surface hoar.Use conservative route selection, stick to moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Wind Slabs

Forecast extreme northeast winds are expected to shift loose surface snow into stiff new wind slabs in exposed lee terrain. Watch for areas that were previously scoured and may become reverse-loaded as the winds switch direction.

Avoid travelling in areas that have been reverse loaded by winds.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Jan 2nd, 2017 2:00PM