Avalanche Forecast

Issued: Feb 13th, 2018 4:07PM

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

Avalanche Canada jlammers, Avalanche Canada

New storm snow will add to the complexity of an already tricky snowpack. Looks like a good day to make conservative terrain choices.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Tuesday

Weather Forecast

Tuesday Night: 10-15cm of new snow / Strong southwest winds / Alpine temperature of -9Wednesday: Generally overcast skies / Moderate northwest winds / Alpine temperature of -13Thursday: Mix of sun and cloud with scattered flurries / Light and variable winds / Alpine temperature of -17Friday: Overcast skies / Moderate northwest winds / Alpine temperature of -10

Avalanche Summary

On Sunday, a remotely-triggered (from a distance) size 1.5, slab avalanche was observed on a southerly aspect at 1700 m. A weak layer buried in early January was the suspected failure plane. A very large, widespread avalanche cycle up to size 4 was observed last Thursday and Friday. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was destroyed. Many of these failed on persistent weak layers mentioned in the snowpack discussion.Looking forward, expect a new round of storm slab activity in response to new snow and wind on Tuesday night. Storm loading has the potential to re-activate deeper, more destructive persistent weak layers.

Snowpack Summary

By Wednesday morning I would expect up to 30cm of new snow. Forecast strong ridgetop winds are expected to redistribute the new snow into much deeper, reactive slabs in wind-exposed terrain.Below the snow surface, several persistent weak layers make up a troublesome snowpack. In the top 1-1.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find at least one of these layers on all aspects and elevations.Deeper in the snowpack (120-200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.

Problems

Storm Slabs

An icon showing Storm Slabs
New snow and wind will form touchy storm slabs. These slabs will cover a variety of old surfaces including extensive wind slabs at upper elevations and crusts on solar aspects and at lower elevations. Pay attention to how the new snow is bonding.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Give cornices a wide berth when traveling on or below ridges.Stay off recent wind loaded areas until the slope has had a chance to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.
Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Be aware of the potential for large, deep avalanches.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 14th, 2018 2:00PM