Avalanche Forecast

Issued: Feb 4th, 2018 5:39PM

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

Avalanche Canada mgrist, Avalanche Canada

Some areas have HIGH avalanche danger due to rapid loading from heavy snowfall and strong winds on Sunday. If you see more than 30 cm of new snow on Monday it's best to avoid all avalanche terrain, free from overhead hazard.

Summary

Confidence

Low - Forecast snowfall amounts are uncertain on Monday

Weather Forecast

Sunday overnight into Monday: 10-15 cm snow Monday: Lingering flurries (5 - 10cm possible) / Light to moderate westerly winds / Freezing level around 1400mTuesday: Flurries (5-10 cm possible) / Moderate west winds / Freezing level around 1200mWednesday: 5-10cm of new snow / Moderate west winds / Freezing level near 1200mNote: Confidence is low for forecast wind values and precipitation amounts on Sunday overnight into Monday.

Avalanche Summary

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

Sunday afternoon saw heavy snowfall (15cm in 5 hours at Kootenay Pass) coupled with moderate to strong south west winds and rising avalanche danger. Elsewhere in the region, storm snow totals over the weekend were on the order of 15-30cm. Winds were gusting moderate at times and created fresh wind slabs on a wide range of aspects at upper elevations. 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 were very touchy on Sunday, with a widespread natural avalanche cycle to size 2.5.
Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.Dial back your terrain choices if you are seeing more than 25cm of new snow.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

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.
Minimize overhead exposure; avalanches may reach the end of run out zones.Be mindful that deep instabilities are still present and have produced recent large avalanches.Good day to make conservative terrain choices.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Feb 5th, 2018 2:00PM

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