Avalanche Forecast

Issued: Feb 5th, 2018 4:45PM

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 mgrist, Avalanche Canada

Storm slabs have been reactive to human triggers, resulting in some surprisingly large avalanches. Several weak layers are lurking deeper in the snowpack: Now is a good time to choose simple terrain, free from overhead hazard.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Tuesday: Isolated flurries (5 cm possible) / Moderate west winds / Freezing level around 900mWednesday: Snow (10-15cm) / Moderate west winds / Freezing level near 1200mThursday: Snow (10-15cm) / Moderate westerly winds / Freezing level around 1400mNote: Confidence is low for forecast wind values and precipitation amounts on Wednesday and Thursday.

Avalanche Summary

On Sunday in the north west part of the region, skiers triggered a size 2.5 avalanche that likely stepped down to the mid January layer. See the MIN report for more details. On Sunday, ski cutting near Nelson produced many soft slab avalanches to size 1.5 on down wind (lee) features that had seen additional snow loading due to wind.Looking forward, expect newly formed storm slabs and the persistent slabs beneath them to remain reactive to human triggers with the potential for very large and destructive avalanches.

Snowpack Summary

Each of the past three days has seen locally heavy snowfall (eg: 15cm in 5 hours at Kootenay Pass on Sunday) coupled with moderate to strong winds at upper elevations. Storm snow totals vary from 25-50 cm and the winds created reactive wind slabs at tree line and above (see Avalanche Summary above). Critical instabilities are buried well below the surface: See this video for a summary of conditions near Nelson. A mixture of weak surface hoar and/or a crust from mid-January is buried beneath all the storm snow at 90-120cm deep. Numerous recent avalanches to size 2.5 have been reported on this layer and large, destructive avalanches at this interface remain a concern.Below this layer lies a second crust/surface hoar interface buried early-January that is now 120-140 cm deep. Several recent avalanches have stepped down to this layer.The mid-December surface hoar layer is buried 130-160 cm below the surface. This layer has continued to produce step down releases and "sudden" test results. It is most pronounced at tree line, but is also present below tree line .

Problems

Storm Slabs

An icon showing Storm Slabs
Storm slabs remained very touchy on Monday, with human triggered avalanches to size 2.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.The new snow will require several days to settle and stabilize.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
The snowpack is complex and continues to produce very large avalanches on several weak layers buried 80 to 150 cm below the surface. Moderate-angled, simple terrain selection remains critical to safe mountain travel.
Good day to make conservative terrain choices.Be mindful that deep instabilities are still present and have produced recent large avalanches.Minimize overhead exposure; avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Feb 6th, 2018 2:00PM