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Avalanche Forecast

Archived

Feb 4th, 2018–Feb 5th, 2018

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary.

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.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.