Avalanche Forecast

Issued: Jan 28th, 2016 7:51AM

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.

Avalanche Canada rbuhler, Avalanche Canada

Recently formed storm slabs are expected to remain touchy on Friday.  Conservative terrain selection remains vital.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A weak ridge of high pressure should dry things out for Thursday night and Friday morning before a weak storm pulse arrives on Friday afternoon. 5-10cm of new snow is expected by Saturday morning with freezing levels around 1000m or lower. Light southeast winds in the morning are expected to become moderate from the southwest in the afternoon. Lingering flurries are expected for Saturday with afternoon freezing levels around 1000m and light alpine winds from the west. A mix of sun and cloud is forecast for Sunday but lingering flurries remain possible.

Avalanche Summary

On Wednesday, two size 1 slab avalanches were accidently triggered by skiers. One was on a northeast aspect at 2150m and failed on the mid-January surface hoar layer down 30cm. The other was on a north aspect at 1900m and also released 30cm down. On Tuesday, a skier accidently triggered a size 1 storm slab avalanche on a northeast aspect at 2000m. The slab released within the recent storm snow down 35cm. On Monday, a skier accidently triggered a size 1 storm slab on a north aspect at 1950m elevation. The slab released within the recent storm snow down 30cm. Recently formed storm slabs are expected to remain reactive to human-triggering on Friday. Extra caution is required where smaller storm slab avalanches have the potential to step down to deeper weak layers that may still be preserved.

Snowpack Summary

New storm snow from Thursday continues to add to the existing storm slab which sits over buried surface hoar in many parts of the region. This surface hoar layer appears to be down 30-40cm and a second more recently buried layer of surface hoar may also be found down around 10-20cm. A thin melt-freeze crust may also be found buried in the upper snowpack but down not seem to be creating an instability. Recently strong south to southwest winds have likely form new wind slabs in leeward features in the alpine. At lower elevations, warm temperatures and rain have likely melted the surface and a melt-freeze crust is expected to form with the cooling trend. The recently destructive early January surface layer is down 60-100cm and is most prominent on all aspects at treeline and below. It is getting harder to trigger this layer but it is still reactive in snowpack tests suggesting that if you are able to trigger it, the layer is capable of wide propagations and large destructive avalanches. A rain crust from December can likely still be found down 100-150cm down but is generally considered inactive. Below this layer the snowpack is generally strong and well settled.

Problems

Storm Slabs

An icon showing Storm Slabs
Recently formed storm slabs overlie a layer of surface hoar layer in many areas and are expected to remain touchy on Friday. Recent strong southwest winds have likely loaded leeward features in wind exposed terrain.
The new snow will require several days to settle and stabilize. >Be cautious as you transition into wind affected terrain. >Storm slabs may be reactive for longer than normal due to the presence of buried surface hoar. >

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
The likelihood of triggering the early-Jan weak layer is slowly dropping but if triggered, this layer can still produce large, destructive avalanches. A cornice failure or a small avalanche in motion has the potential step-down to a deeper weak layer
Be aware of the potential for large avalanches due to the presence of buried surface hoar. >Dig down to find and test weak layers before committing to a big line. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Valid until: Jan 29th, 2016 2:00PM

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